Merge remote-tracking branch 'goog/upstream-master' into androidx-platform-dev

* goog/upstream-master:
  Update Icing from upstream.
  Update Icing from upstream.

Descriptions:
========================================================================
Cache an instance of UBreakIterator to reduce unnecessary creations.
========================================================================
Cap number of individual IntegerIndexStorages that IntegerIndex creates.
========================================================================
Change error in trimRightMostNode from Unimplemented to InvalidArgument.
========================================================================
Add detection for new language features of List Filters Query Language.
========================================================================
Add option to control threshold to rebuild index during optimize by flag
========================================================================
Add option to control use of namespace id to build urimapper by flag.
========================================================================
Enforce schema validation for joinable config.
========================================================================
Adopt bucket splitting for IntegerIndexStorage.
========================================================================
Implement bucket splitting function.
========================================================================
Add Icing initialization unit tests for QualifiedIdTypeJoinableIndex.
========================================================================
Add Icing schema change unit tests for QualifiedIdTypeJoinableIndex.
========================================================================
Add Icing optimization unit tests for QualifiedIdTypeJoinableIndex.
========================================================================
Integrate QualifiedIdTypeJoinableIndex into IcingSearchEngine.
========================================================================
Implement QualifiedIdJoinablePropertyIndexingHandler.
========================================================================
Change QualifiedIdTypeJoinableIndex to store raw qualified id string.
========================================================================
Pass info about unnormalized query terms through lexer/parser/visitor.
========================================================================
Integrate Advanced Query w/ Suggest, make ADVANCED_QUERY default parser.
======================================================================

Bug: 208654892
Bug: 263890397
Bug: 259743562
Bug: 272145329
Bug: 227356108
Change-Id: I44de5853bb6c55b42800ae34d8071016be6c87cd

85 files changed, 10741 insertions, 1692 deletions

diff --git a/icing/file/file-backed-proto.h b/icing/file/file-backed-proto.h
index 8deb7a6..8c5743b 100644
--- a/icing/file/file-backed-proto.h
+++ b/icing/file/file-backed-proto.h
@@ -22,6 +22,7 @@
 #ifndef ICING_FILE_FILE_BACKED_PROTO_H_
 #define ICING_FILE_FILE_BACKED_PROTO_H_
 
+#include <algorithm>
 #include <cstdint>
 #include <memory>
 #include <string>
@@ -37,6 +38,7 @@
 #include "icing/legacy/core/icing-string-util.h"
 #include "icing/util/crc32.h"
 #include "icing/util/logging.h"
+#include "icing/util/status-macros.h"
 
 namespace icing {
 namespace lib {
@@ -74,6 +76,13 @@ class FileBackedProto {
     file_path_ = swapped_to_file_path;
   }
 
+  // Computes the checksum of the proto stored in this file and returns it.
+  // RETURNS:
+  //   - the checksum of the proto or 0 if the file is empty/non-existent
+  //   - INTERNAL_ERROR if an IO error or a corruption was encountered.
+  libtextclassifier3::StatusOr<Crc32> ComputeChecksum() const
+      ICING_LOCKS_EXCLUDED(mutex_);
+
   // Returns a reference to the proto read from the file. It
   // internally caches the read proto so that future calls are fast.
   //
@@ -103,6 +112,11 @@ class FileBackedProto {
   FileBackedProto& operator=(const FileBackedProto&) = delete;
 
  private:
+  // Internal method to handle reading the proto from disk.
+  // Requires the caller to hold an exclusive lock on mutex_.
+  libtextclassifier3::StatusOr<const ProtoT*> ReadInternal() const
+      ICING_EXCLUSIVE_LOCKS_REQUIRED(mutex_);
+
   // Upper bound of file-size that is supported.
   static constexpr int32_t kMaxFileSize = 1 * 1024 * 1024;  // 1 MiB.
 
@@ -113,6 +127,8 @@ class FileBackedProto {
   std::string file_path_;
 
   mutable std::unique_ptr<ProtoT> cached_proto_ ICING_GUARDED_BY(mutex_);
+
+  mutable std::unique_ptr<Header> cached_header_ ICING_GUARDED_BY(mutex_);
 };
 
 template <typename ProtoT>
@@ -124,12 +140,35 @@ FileBackedProto<ProtoT>::FileBackedProto(const Filesystem& filesystem,
     : filesystem_(&filesystem), file_path_(file_path) {}
 
 template <typename ProtoT>
+libtextclassifier3::StatusOr<Crc32> FileBackedProto<ProtoT>::ComputeChecksum()
+    const {
+  absl_ports::unique_lock l(&mutex_);
+  if (cached_proto_ == nullptr) {
+    auto read_status = ReadInternal();
+    if (!read_status.ok()) {
+      if (absl_ports::IsNotFound(read_status.status())) {
+        // File doesn't exist. So simply return 0.
+        return Crc32();
+      }
+      return read_status.status();
+    }
+  }
+  return Crc32(cached_header_->proto_checksum);
+}
+
+template <typename ProtoT>
 libtextclassifier3::StatusOr<const ProtoT*> FileBackedProto<ProtoT>::Read()
     const {
   ICING_VLOG(1) << "Reading proto from file: " << file_path_;
 
   absl_ports::unique_lock l(&mutex_);
 
+  return ReadInternal();
+}
+
+template <typename ProtoT>
+libtextclassifier3::StatusOr<const ProtoT*>
+FileBackedProto<ProtoT>::ReadInternal() const {
   // Return cached proto if we've already read from disk.
   if (cached_proto_ != nullptr) {
     ICING_VLOG(1) << "Reusing cached proto for file: " << file_path_;
@@ -157,8 +196,7 @@ libtextclassifier3::StatusOr<const ProtoT*> FileBackedProto<ProtoT>::Read()
                 << " of size: " << file_size;
 
   Header header;
-  if (!filesystem_->PRead(fd.get(), &header, sizeof(Header),
-                          /*offset=*/0)) {
+  if (!filesystem_->PRead(fd.get(), &header, sizeof(Header), /*offset=*/0)) {
     return absl_ports::InternalError(
         absl_ports::StrCat("Unable to read header of: ", file_path_));
   }
@@ -193,6 +231,7 @@ libtextclassifier3::StatusOr<const ProtoT*> FileBackedProto<ProtoT>::Read()
 
   ICING_VLOG(1) << "Successfully read proto from file: " << file_path_;
   cached_proto_ = std::move(proto);
+  cached_header_ = std::make_unique<Header>(std::move(header));
   return cached_proto_.get();
 }
 
@@ -253,6 +292,7 @@ libtextclassifier3::Status FileBackedProto<ProtoT>::Write(
 
   ICING_VLOG(1) << "Successfully wrote proto to file: " << file_path_;
   cached_proto_ = std::move(new_proto);
+  cached_header_ = std::make_unique<Header>(std::move(header));
   return libtextclassifier3::Status::OK;
 }
 
diff --git a/icing/file/persistent-hash-map.cc b/icing/file/persistent-hash-map.cc
index 14a1251..ce8310b 100644
--- a/icing/file/persistent-hash-map.cc
+++ b/icing/file/persistent-hash-map.cc
@@ -147,7 +147,9 @@ PersistentHashMap::Create(const Filesystem& filesystem,
       !filesystem.FileExists(
           GetKeyValueStorageFilePath(working_path).c_str())) {
     // Discard working_path if any of them is missing, and reinitialize.
-    ICING_RETURN_IF_ERROR(Discard(filesystem, working_path));
+    if (filesystem.DirectoryExists(working_path.c_str())) {
+      ICING_RETURN_IF_ERROR(Discard(filesystem, working_path));
+    }
     return InitializeNewFiles(filesystem, std::move(working_path),
                               std::move(options));
   }
diff --git a/icing/file/posting_list/flash-index-storage.cc b/icing/file/posting_list/flash-index-storage.cc
index 657bd96..2ba24a3 100644
--- a/icing/file/posting_list/flash-index-storage.cc
+++ b/icing/file/posting_list/flash-index-storage.cc
@@ -37,22 +37,6 @@
 namespace icing {
 namespace lib {
 
-namespace {
-
-uint32_t SelectBlockSize() {
-  // This should be close to the flash page size.
-  static constexpr uint32_t kMinBlockSize = 4096;
-
-  // Determine a good block size.
-  uint32_t page_size = getpagesize();
-  uint32_t block_size = std::max(kMinBlockSize, page_size);
-
-  // Align up to the nearest page size.
-  return math_util::RoundUpTo(block_size, page_size);
-}
-
-}  // namespace
-
 libtextclassifier3::StatusOr<FlashIndexStorage> FlashIndexStorage::Create(
     std::string index_filename, const Filesystem* filesystem,
     PostingListSerializer* serializer, bool in_memory) {
@@ -75,6 +59,18 @@ FlashIndexStorage::~FlashIndexStorage() {
   }
 }
 
+/* static */ uint32_t FlashIndexStorage::SelectBlockSize() {
+  // This should be close to the flash page size.
+  static constexpr uint32_t kMinBlockSize = 4096;
+
+  // Determine a good block size.
+  uint32_t page_size = getpagesize();
+  uint32_t block_size = std::max(kMinBlockSize, page_size);
+
+  // Align up to the nearest page size.
+  return math_util::RoundUpTo(block_size, page_size);
+}
+
 bool FlashIndexStorage::Init() {
   storage_sfd_ = ScopedFd(filesystem_->OpenForWrite(index_filename_.c_str()));
   if (!storage_sfd_.is_valid()) {
diff --git a/icing/file/posting_list/flash-index-storage.h b/icing/file/posting_list/flash-index-storage.h
index 1813637..05feb08 100644
--- a/icing/file/posting_list/flash-index-storage.h
+++ b/icing/file/posting_list/flash-index-storage.h
@@ -105,6 +105,9 @@ class FlashIndexStorage {
 
   ~FlashIndexStorage();
 
+  // Selects block size to use.
+  static uint32_t SelectBlockSize();
+
   // Retrieves the PostingList referred to by PostingListIdentifier. This
   // posting list must have been previously allocated by a prior call to
   // AllocatePostingList.
diff --git a/icing/icing-search-engine.cc b/icing/icing-search-engine.cc
index 1b193af..7800e7e 100644
--- a/icing/icing-search-engine.cc
+++ b/icing/icing-search-engine.cc
@@ -41,6 +41,8 @@
 #include "icing/index/numeric/integer-index.h"
 #include "icing/index/string-section-indexing-handler.h"
 #include "icing/join/join-processor.h"
+#include "icing/join/qualified-id-joinable-property-indexing-handler.h"
+#include "icing/join/qualified-id-type-joinable-index.h"
 #include "icing/legacy/index/icing-filesystem.h"
 #include "icing/portable/endian.h"
 #include "icing/proto/debug.pb.h"
@@ -96,6 +98,8 @@ namespace {
 constexpr std::string_view kDocumentSubfolderName = "document_dir";
 constexpr std::string_view kIndexSubfolderName = "index_dir";
 constexpr std::string_view kIntegerIndexSubfolderName = "integer_index_dir";
+constexpr std::string_view kQualifiedIdJoinIndexSubfolderName =
+    "qualified_id_join_index_dir";
 constexpr std::string_view kSchemaSubfolderName = "schema_dir";
 constexpr std::string_view kSetSchemaMarkerFilename = "set_schema_marker";
 constexpr std::string_view kInitMarkerFilename = "init_marker";
@@ -240,6 +244,14 @@ std::string MakeIntegerIndexWorkingPath(const std::string& base_dir) {
   return absl_ports::StrCat(base_dir, "/", kIntegerIndexSubfolderName);
 }
 
+// Working path for qualified id join index. It is derived from
+// PersistentStorage and it will take full ownership of this working path,
+// including creation/deletion. See PersistentStorage for more details about
+// working path.
+std::string MakeQualifiedIdJoinIndexWorkingPath(const std::string& base_dir) {
+  return absl_ports::StrCat(base_dir, "/", kQualifiedIdJoinIndexSubfolderName);
+}
+
 // SchemaStore files are in a standalone subfolder for easier file management.
 // We can delete and recreate the subfolder and not touch/affect anything
 // else.
@@ -347,15 +359,12 @@ libtextclassifier3::Status RetrieveAndAddDocumentInfo(
   return libtextclassifier3::Status::OK;
 }
 
-bool ShouldRebuildIndex(const OptimizeStatsProto& optimize_stats) {
+bool ShouldRebuildIndex(const OptimizeStatsProto& optimize_stats,
+                        float optimize_rebuild_index_threshold) {
   int num_invalid_documents = optimize_stats.num_deleted_documents() +
                               optimize_stats.num_expired_documents();
-  // Rebuilding the index could be faster than optimizing the index if we have
-  // removed most of the documents.
-  // Based on benchmarks, 85%~95% seems to be a good threshold for most cases.
-  // TODO(b/238236206): Try using the number of remaining hits in this
-  // condition, and allow clients to configure the threshold.
-  return num_invalid_documents >= optimize_stats.num_original_documents() * 0.9;
+  return num_invalid_documents >= optimize_stats.num_original_documents() *
+                                      optimize_rebuild_index_threshold;
 }
 
 // Useful method to get RankingStrategy if advanced scoring is enabled. When the
@@ -428,6 +437,7 @@ void IcingSearchEngine::ResetMembers() {
   normalizer_.reset();
   index_.reset();
   integer_index_.reset();
+  qualified_id_join_index_.reset();
 }
 
 libtextclassifier3::Status IcingSearchEngine::CheckInitMarkerFile(
@@ -559,12 +569,17 @@ libtextclassifier3::Status IcingSearchEngine::InitializeMembers(
     const std::string index_dir = MakeIndexDirectoryPath(options_.base_dir());
     const std::string integer_index_dir =
         MakeIntegerIndexWorkingPath(options_.base_dir());
+    const std::string qualified_id_join_index_dir =
+        MakeQualifiedIdJoinIndexWorkingPath(options_.base_dir());
     if (!filesystem_->DeleteDirectoryRecursively(doc_store_dir.c_str()) ||
         !filesystem_->DeleteDirectoryRecursively(index_dir.c_str()) ||
-        !IntegerIndex::Discard(*filesystem_, integer_index_dir).ok()) {
-      return absl_ports::InternalError(
-          absl_ports::StrCat("Could not delete directories: ", index_dir, ", ",
-                             integer_index_dir, " and", doc_store_dir));
+        !IntegerIndex::Discard(*filesystem_, integer_index_dir).ok() ||
+        !QualifiedIdTypeJoinableIndex::Discard(*filesystem_,
+                                               qualified_id_join_index_dir)
+             .ok()) {
+      return absl_ports::InternalError(absl_ports::StrCat(
+          "Could not delete directories: ", index_dir, ", ", integer_index_dir,
+          ", ", qualified_id_join_index_dir, " and ", doc_store_dir));
     }
     ICING_RETURN_IF_ERROR(InitializeDocumentStore(
         /*force_recovery_and_revalidate_documents=*/false, initialize_stats));
@@ -601,6 +616,16 @@ libtextclassifier3::Status IcingSearchEngine::InitializeMembers(
         integer_index_,
         IntegerIndex::Create(*filesystem_, std::move(integer_index_dir)));
 
+    // Discard qualified id join index directory and instantiate a new one.
+    std::string qualified_id_join_index_dir =
+        MakeQualifiedIdJoinIndexWorkingPath(options_.base_dir());
+    ICING_RETURN_IF_ERROR(QualifiedIdTypeJoinableIndex::Discard(
+        *filesystem_, qualified_id_join_index_dir));
+    ICING_ASSIGN_OR_RETURN(
+        qualified_id_join_index_,
+        QualifiedIdTypeJoinableIndex::Create(
+            *filesystem_, std::move(qualified_id_join_index_dir)));
+
     std::unique_ptr<Timer> restore_timer = clock_->GetNewTimer();
     IndexRestorationResult restore_result = RestoreIndexIfNeeded();
     index_init_status = std::move(restore_result.status);
@@ -621,6 +646,8 @@ libtextclassifier3::Status IcingSearchEngine::InitializeMembers(
         InitializeStatsProto::SCHEMA_CHANGES_OUT_OF_SYNC);
     initialize_stats->set_integer_index_restoration_cause(
         InitializeStatsProto::SCHEMA_CHANGES_OUT_OF_SYNC);
+    initialize_stats->set_qualified_id_join_index_restoration_cause(
+        InitializeStatsProto::SCHEMA_CHANGES_OUT_OF_SYNC);
   } else {
     ICING_RETURN_IF_ERROR(InitializeDocumentStore(
         /*force_recovery_and_revalidate_documents=*/false, initialize_stats));
@@ -673,9 +700,11 @@ libtextclassifier3::Status IcingSearchEngine::InitializeDocumentStore(
   }
   ICING_ASSIGN_OR_RETURN(
       DocumentStore::CreateResult create_result,
-      DocumentStore::Create(
-          filesystem_.get(), document_dir, clock_.get(), schema_store_.get(),
-          force_recovery_and_revalidate_documents, initialize_stats));
+      DocumentStore::Create(filesystem_.get(), document_dir, clock_.get(),
+                            schema_store_.get(),
+                            force_recovery_and_revalidate_documents,
+                            options_.document_store_namespace_id_fingerprint(),
+                            initialize_stats));
   document_store_ = std::move(create_result.document_store);
 
   return libtextclassifier3::Status::OK;
@@ -693,6 +722,7 @@ libtextclassifier3::Status IcingSearchEngine::InitializeIndex(
   }
   Index::Options index_options(index_dir, options_.index_merge_size());
 
+  // Term index
   InitializeStatsProto::RecoveryCause index_recovery_cause;
   auto index_or =
       Index::Create(index_options, filesystem_.get(), icing_filesystem_.get());
@@ -717,6 +747,7 @@ libtextclassifier3::Status IcingSearchEngine::InitializeIndex(
     index_recovery_cause = InitializeStatsProto::INCONSISTENT_WITH_GROUND_TRUTH;
   }
 
+  // Integer index
   std::string integer_index_dir =
       MakeIntegerIndexWorkingPath(options_.base_dir());
   InitializeStatsProto::RecoveryCause integer_index_recovery_cause;
@@ -740,10 +771,38 @@ libtextclassifier3::Status IcingSearchEngine::InitializeIndex(
         InitializeStatsProto::INCONSISTENT_WITH_GROUND_TRUTH;
   }
 
+  // Qualified id join index
+  std::string qualified_id_join_index_dir =
+      MakeQualifiedIdJoinIndexWorkingPath(options_.base_dir());
+  InitializeStatsProto::RecoveryCause qualified_id_join_index_recovery_cause;
+  auto qualified_id_join_index_or = QualifiedIdTypeJoinableIndex::Create(
+      *filesystem_, qualified_id_join_index_dir);
+  if (!qualified_id_join_index_or.ok()) {
+    ICING_RETURN_IF_ERROR(QualifiedIdTypeJoinableIndex::Discard(
+        *filesystem_, qualified_id_join_index_dir));
+
+    qualified_id_join_index_recovery_cause = InitializeStatsProto::IO_ERROR;
+
+    // Try recreating it from scratch and rebuild everything.
+    ICING_ASSIGN_OR_RETURN(
+        qualified_id_join_index_,
+        QualifiedIdTypeJoinableIndex::Create(
+            *filesystem_, std::move(qualified_id_join_index_dir)));
+  } else {
+    // Qualified id join index was created fine.
+    qualified_id_join_index_ =
+        std::move(qualified_id_join_index_or).ValueOrDie();
+    // If a recover does have to happen, then it must be because the index is
+    // out of sync with the document store.
+    qualified_id_join_index_recovery_cause =
+        InitializeStatsProto::INCONSISTENT_WITH_GROUND_TRUTH;
+  }
+
   std::unique_ptr<Timer> restore_timer = clock_->GetNewTimer();
   IndexRestorationResult restore_result = RestoreIndexIfNeeded();
   if (restore_result.index_needed_restoration ||
-      restore_result.integer_index_needed_restoration) {
+      restore_result.integer_index_needed_restoration ||
+      restore_result.qualified_id_join_index_needed_restoration) {
     initialize_stats->set_index_restoration_latency_ms(
         restore_timer->GetElapsedMilliseconds());
 
@@ -754,6 +813,10 @@ libtextclassifier3::Status IcingSearchEngine::InitializeIndex(
       initialize_stats->set_integer_index_restoration_cause(
           integer_index_recovery_cause);
     }
+    if (restore_result.qualified_id_join_index_needed_restoration) {
+      initialize_stats->set_qualified_id_join_index_restoration_cause(
+          qualified_id_join_index_recovery_cause);
+    }
   }
   return restore_result.status;
 }
@@ -863,20 +926,25 @@ SetSchemaResultProto IcingSearchEngine::SetSchema(
       }
     }
 
-    if (lost_previous_schema || join_incompatible) {
-      // TODO(b/256022027): rebuild joinable cache if not join compatible. This
-      //   should be done together with index (see RestoreIndexIfNeeded) because
-      //   we want to "replay" documents only once to cover all rebuild.
+    if (lost_previous_schema || index_incompatible) {
+      // Clears search indices
+      status = ClearSearchIndices();
+      if (!status.ok()) {
+        TransformStatus(status, result_status);
+        return result_proto;
+      }
     }
 
-    if (lost_previous_schema || index_incompatible) {
-      // Clears all indices
-      status = ClearIndices();
+    if (lost_previous_schema || join_incompatible) {
+      // Clears join indices
+      status = ClearJoinIndices();
       if (!status.ok()) {
         TransformStatus(status, result_status);
         return result_proto;
       }
+    }
 
+    if (lost_previous_schema || index_incompatible || join_incompatible) {
       IndexRestorationResult restore_result = RestoreIndexIfNeeded();
       // DATA_LOSS means that we have successfully re-added content to the
       // index. Some indexed content was lost, but otherwise the index is in a
@@ -996,12 +1064,12 @@ PutResultProto IcingSearchEngine::Put(DocumentProto&& document) {
   auto index_status = index_processor.IndexDocument(
       tokenized_document, document_id, put_document_stats);
   // Getting an internal error from the index could possibly mean that the index
-  // is broken. Try to rebuild the index to recover.
+  // is broken. Try to rebuild them to recover.
   if (absl_ports::IsInternal(index_status)) {
     ICING_LOG(ERROR) << "Got an internal error from the index. Trying to "
                         "rebuild the index!\n"
                      << index_status.error_message();
-    index_status = ClearIndices();
+    index_status = ClearAllIndices();
     if (index_status.ok()) {
       index_status = RestoreIndexIfNeeded().status;
       if (!index_status.ok()) {
@@ -1009,8 +1077,8 @@ PutResultProto IcingSearchEngine::Put(DocumentProto&& document) {
                             "indexing a document.";
       }
     } else {
-      ICING_LOG(ERROR) << "Failed to clear the index after a failure of "
-                          "indexing a document.";
+      ICING_LOG(ERROR)
+          << "Failed to clear indices after a failure of indexing a document.";
     }
   }
 
@@ -1411,7 +1479,9 @@ OptimizeResultProto IcingSearchEngine::Optimize() {
   // guaranteed to work, so we update index according to the new document store.
   std::unique_ptr<Timer> optimize_index_timer = clock_->GetNewTimer();
   bool should_rebuild_index =
-      !document_id_old_to_new_or.ok() || ShouldRebuildIndex(*optimize_stats);
+      !document_id_old_to_new_or.ok() ||
+      ShouldRebuildIndex(*optimize_stats,
+                         options_.optimize_rebuild_index_threshold());
   if (!should_rebuild_index) {
     optimize_stats->set_index_restoration_mode(
         OptimizeStatsProto::INDEX_TRANSLATION);
@@ -1432,6 +1502,17 @@ OptimizeResultProto IcingSearchEngine::Optimize() {
                          << integer_index_optimize_status.error_message();
       should_rebuild_index = true;
     }
+
+    libtextclassifier3::Status qualified_id_join_index_optimize_status =
+        qualified_id_join_index_->Optimize(
+            document_id_old_to_new_or.ValueOrDie(),
+            document_store_->last_added_document_id());
+    if (!qualified_id_join_index_optimize_status.ok()) {
+      ICING_LOG(WARNING)
+          << "Failed to optimize qualified id join index. Error: "
+          << qualified_id_join_index_optimize_status.error_message();
+      should_rebuild_index = true;
+    }
   }
   // If we received a DATA_LOSS error from OptimizeDocumentStore, we have a
   // valid document store, but it might be the old one or the new one. So throw
@@ -1445,7 +1526,7 @@ OptimizeResultProto IcingSearchEngine::Optimize() {
         OptimizeStatsProto::FULL_INDEX_REBUILD);
     ICING_LOG(WARNING) << "Clearing the entire index!";
 
-    libtextclassifier3::Status index_clear_status = ClearIndices();
+    libtextclassifier3::Status index_clear_status = ClearAllIndices();
     if (!index_clear_status.ok()) {
       status = absl_ports::Annotate(
           absl_ports::InternalError("Failed to clear index."),
@@ -1652,6 +1733,7 @@ libtextclassifier3::Status IcingSearchEngine::InternalPersistToDisk(
   ICING_RETURN_IF_ERROR(document_store_->PersistToDisk(PersistType::FULL));
   ICING_RETURN_IF_ERROR(index_->PersistToDisk());
   ICING_RETURN_IF_ERROR(integer_index_->PersistToDisk());
+  ICING_RETURN_IF_ERROR(qualified_id_join_index_->PersistToDisk());
 
   return libtextclassifier3::Status::OK;
 }
@@ -1714,7 +1796,8 @@ SearchResultProto IcingSearchEngine::Search(
       return result_proto;
     }
 
-    JoinProcessor join_processor(document_store_.get());
+    JoinProcessor join_processor(document_store_.get(), schema_store_.get(),
+                                 qualified_id_join_index_.get());
     // Building a JoinChildrenFetcher where child documents are grouped by
     // their joinable values.
     libtextclassifier3::StatusOr<JoinChildrenFetcher> join_children_fetcher_or =
@@ -1756,7 +1839,8 @@ SearchResultProto IcingSearchEngine::Search(
   std::unique_ptr<ScoredDocumentHitsRanker> ranker;
   if (join_children_fetcher != nullptr) {
     // Join 2 scored document hits
-    JoinProcessor join_processor(document_store_.get());
+    JoinProcessor join_processor(document_store_.get(), schema_store_.get(),
+                                 qualified_id_join_index_.get());
     libtextclassifier3::StatusOr<std::vector<JoinedScoredDocumentHit>>
         joined_result_document_hits_or = join_processor.Join(
             join_spec, std::move(query_scoring_results.scored_document_hits),
@@ -2042,9 +2126,10 @@ IcingSearchEngine::OptimizeDocumentStore(OptimizeStatsProto* optimize_stats) {
 
     // Tries to rebuild document store if swapping fails, to avoid leaving the
     // system in the broken state for future operations.
-    auto create_result_or =
-        DocumentStore::Create(filesystem_.get(), current_document_dir,
-                              clock_.get(), schema_store_.get());
+    auto create_result_or = DocumentStore::Create(
+        filesystem_.get(), current_document_dir, clock_.get(),
+        schema_store_.get(), /*force_recovery_and_revalidate_documents=*/false,
+        options_.document_store_namespace_id_fingerprint());
     // TODO(b/144458732): Implement a more robust version of
     // TC_ASSIGN_OR_RETURN that can support error logging.
     if (!create_result_or.ok()) {
@@ -2068,9 +2153,10 @@ IcingSearchEngine::OptimizeDocumentStore(OptimizeStatsProto* optimize_stats) {
   }
 
   // Recreates the doc store instance
-  auto create_result_or =
-      DocumentStore::Create(filesystem_.get(), current_document_dir,
-                            clock_.get(), schema_store_.get());
+  auto create_result_or = DocumentStore::Create(
+      filesystem_.get(), current_document_dir, clock_.get(),
+      schema_store_.get(), /*force_recovery_and_revalidate_documents=*/false,
+      options_.document_store_namespace_id_fingerprint());
   if (!create_result_or.ok()) {
     // Unable to create DocumentStore from the new file. Mark as uninitialized
     // and return INTERNAL.
@@ -2098,34 +2184,37 @@ IcingSearchEngine::RestoreIndexIfNeeded() {
   DocumentId last_stored_document_id =
       document_store_->last_added_document_id();
   if (last_stored_document_id == index_->last_added_document_id() &&
-      last_stored_document_id == integer_index_->last_added_document_id()) {
+      last_stored_document_id == integer_index_->last_added_document_id() &&
+      last_stored_document_id ==
+          qualified_id_join_index_->last_added_document_id()) {
     // No need to recover.
-    return {libtextclassifier3::Status::OK, false, false};
+    return {libtextclassifier3::Status::OK, false, false, false};
   }
 
   if (last_stored_document_id == kInvalidDocumentId) {
     // Document store is empty but index is not. Clear the index.
-    return {ClearIndices(), false, false};
+    return {ClearAllIndices(), false, false, false};
   }
 
   // Truncate indices first.
   auto truncate_result_or = TruncateIndicesTo(last_stored_document_id);
   if (!truncate_result_or.ok()) {
-    return {std::move(truncate_result_or).status(), false, false};
+    return {std::move(truncate_result_or).status(), false, false, false};
   }
   TruncateIndexResult truncate_result =
       std::move(truncate_result_or).ValueOrDie();
 
   if (truncate_result.first_document_to_reindex > last_stored_document_id) {
     // Nothing to restore. Just return.
-    return {libtextclassifier3::Status::OK, false, false};
+    return {libtextclassifier3::Status::OK, false, false, false};
   }
 
   auto data_indexing_handlers_or = CreateDataIndexingHandlers();
   if (!data_indexing_handlers_or.ok()) {
     return {data_indexing_handlers_or.status(),
             truncate_result.index_needed_restoration,
-            truncate_result.integer_index_needed_restoration};
+            truncate_result.integer_index_needed_restoration,
+            truncate_result.qualified_id_join_index_needed_restoration};
   }
   // By using recovery_mode for IndexProcessor, we're able to replay documents
   // from smaller document id and it will skip documents that are already been
@@ -2151,7 +2240,8 @@ IcingSearchEngine::RestoreIndexIfNeeded() {
       } else {
         // Returns other errors
         return {document_or.status(), truncate_result.index_needed_restoration,
-                truncate_result.integer_index_needed_restoration};
+                truncate_result.integer_index_needed_restoration,
+                truncate_result.qualified_id_join_index_needed_restoration};
       }
     }
     DocumentProto document(std::move(document_or).ValueOrDie());
@@ -2163,7 +2253,8 @@ IcingSearchEngine::RestoreIndexIfNeeded() {
     if (!tokenized_document_or.ok()) {
       return {tokenized_document_or.status(),
               truncate_result.index_needed_restoration,
-              truncate_result.integer_index_needed_restoration};
+              truncate_result.integer_index_needed_restoration,
+              truncate_result.qualified_id_join_index_needed_restoration};
     }
     TokenizedDocument tokenized_document(
         std::move(tokenized_document_or).ValueOrDie());
@@ -2174,7 +2265,8 @@ IcingSearchEngine::RestoreIndexIfNeeded() {
       if (!absl_ports::IsDataLoss(status)) {
         // Real error. Stop recovering and pass it up.
         return {status, truncate_result.index_needed_restoration,
-                truncate_result.integer_index_needed_restoration};
+                truncate_result.integer_index_needed_restoration,
+                truncate_result.qualified_id_join_index_needed_restoration};
       }
       // FIXME: why can we skip data loss error here?
       // Just a data loss. Keep trying to add the remaining docs, but report the
@@ -2184,7 +2276,8 @@ IcingSearchEngine::RestoreIndexIfNeeded() {
   }
 
   return {overall_status, truncate_result.index_needed_restoration,
-          truncate_result.integer_index_needed_restoration};
+          truncate_result.integer_index_needed_restoration,
+          truncate_result.qualified_id_join_index_needed_restoration};
 }
 
 libtextclassifier3::StatusOr<bool> IcingSearchEngine::LostPreviousSchema() {
@@ -2228,7 +2321,14 @@ IcingSearchEngine::CreateDataIndexingHandlers() {
                              clock_.get(), integer_index_.get()));
   handlers.push_back(std::move(integer_section_indexing_handler));
 
-  // TODO(b/263890397): add QualifiedIdJoinablePropertyIndexingHandler
+  // Qualified id joinable property index handler
+  ICING_ASSIGN_OR_RETURN(
+      std::unique_ptr<QualifiedIdJoinablePropertyIndexingHandler>
+          qualified_id_joinable_property_indexing_handler,
+      QualifiedIdJoinablePropertyIndexingHandler::Create(
+          clock_.get(), qualified_id_join_index_.get()));
+  handlers.push_back(
+      std::move(qualified_id_joinable_property_indexing_handler));
 
   return handlers;
 }
@@ -2265,11 +2365,12 @@ IcingSearchEngine::TruncateIndicesTo(DocumentId last_stored_document_id) {
     // starting from integer_index_last_added_document_id + 1. Also use std::min
     // since we might need to replay even smaller doc ids for term index.
     integer_index_needed_restoration = true;
-    first_document_to_reindex =
-        integer_index_last_added_document_id != kInvalidDocumentId
-            ? std::min(first_document_to_reindex,
-                       integer_index_last_added_document_id + 1)
-            : kMinDocumentId;
+    if (integer_index_last_added_document_id != kInvalidDocumentId) {
+      first_document_to_reindex = std::min(
+          first_document_to_reindex, integer_index_last_added_document_id + 1);
+    } else {
+      first_document_to_reindex = kMinDocumentId;
+    }
   } else if (last_stored_document_id < integer_index_last_added_document_id) {
     // Clear the entire integer index if last_stored_document_id is smaller than
     // integer_index_last_added_document_id, because there is no way to remove
@@ -2283,17 +2384,62 @@ IcingSearchEngine::TruncateIndicesTo(DocumentId last_stored_document_id) {
     first_document_to_reindex = kMinDocumentId;
   }
 
+  // Attempt to truncate qualified id join index
+  bool qualified_id_join_index_needed_restoration = false;
+  DocumentId qualified_id_join_index_last_added_document_id =
+      qualified_id_join_index_->last_added_document_id();
+  if (qualified_id_join_index_last_added_document_id == kInvalidDocumentId ||
+      last_stored_document_id >
+          qualified_id_join_index_last_added_document_id) {
+    // If last_stored_document_id is greater than
+    // qualified_id_join_index_last_added_document_id, then we only have to
+    // replay docs starting from (qualified_id_join_index_last_added_document_id
+    // + 1). Also use std::min since we might need to replay even smaller doc
+    // ids for other components.
+    qualified_id_join_index_needed_restoration = true;
+    if (qualified_id_join_index_last_added_document_id != kInvalidDocumentId) {
+      first_document_to_reindex =
+          std::min(first_document_to_reindex,
+                   qualified_id_join_index_last_added_document_id + 1);
+    } else {
+      first_document_to_reindex = kMinDocumentId;
+    }
+  } else if (last_stored_document_id <
+             qualified_id_join_index_last_added_document_id) {
+    // Clear the entire qualified id join index if last_stored_document_id is
+    // smaller than qualified_id_join_index_last_added_document_id, because
+    // there is no way to remove data with doc_id > last_stored_document_id from
+    // join index efficiently and we have to rebuild.
+    ICING_RETURN_IF_ERROR(qualified_id_join_index_->Clear());
+
+    // Since the entire qualified id join index is discarded, we start to
+    // rebuild it by setting first_document_to_reindex to kMinDocumentId.
+    qualified_id_join_index_needed_restoration = true;
+    first_document_to_reindex = kMinDocumentId;
+  }
+
   return TruncateIndexResult(first_document_to_reindex,
                              index_needed_restoration,
-                             integer_index_needed_restoration);
+                             integer_index_needed_restoration,
+                             qualified_id_join_index_needed_restoration);
 }
 
-libtextclassifier3::Status IcingSearchEngine::ClearIndices() {
+libtextclassifier3::Status IcingSearchEngine::ClearSearchIndices() {
   ICING_RETURN_IF_ERROR(index_->Reset());
   ICING_RETURN_IF_ERROR(integer_index_->Clear());
   return libtextclassifier3::Status::OK;
 }
 
+libtextclassifier3::Status IcingSearchEngine::ClearJoinIndices() {
+  return qualified_id_join_index_->Clear();
+}
+
+libtextclassifier3::Status IcingSearchEngine::ClearAllIndices() {
+  ICING_RETURN_IF_ERROR(ClearSearchIndices());
+  ICING_RETURN_IF_ERROR(ClearJoinIndices());
+  return libtextclassifier3::Status::OK;
+}
+
 ResetResultProto IcingSearchEngine::Reset() {
   absl_ports::unique_lock l(&mutex_);
   return ResetInternal();
diff --git a/icing/icing-search-engine.h b/icing/icing-search-engine.h
index 678fc77..3e85f69 100644
--- a/icing/icing-search-engine.h
+++ b/icing/icing-search-engine.h
@@ -31,6 +31,7 @@
 #include "icing/index/numeric/numeric-index.h"
 #include "icing/jni/jni-cache.h"
 #include "icing/join/join-children-fetcher.h"
+#include "icing/join/qualified-id-type-joinable-index.h"
 #include "icing/legacy/index/icing-filesystem.h"
 #include "icing/performance-configuration.h"
 #include "icing/proto/debug.pb.h"
@@ -474,10 +475,13 @@ class IcingSearchEngine {
   std::unique_ptr<Index> index_ ICING_GUARDED_BY(mutex_);
 
   // Storage for all hits of numeric contents from the document store.
-  // TODO(b/249829533): integrate more functions with integer_index_.
   std::unique_ptr<NumericIndex<int64_t>> integer_index_
       ICING_GUARDED_BY(mutex_);
 
+  // Storage for all join qualified ids from the document store.
+  std::unique_ptr<QualifiedIdTypeJoinableIndex> qualified_id_join_index_
+      ICING_GUARDED_BY(mutex_);
+
   // Pointer to JNI class references
   const std::unique_ptr<const JniCache> jni_cache_;
 
@@ -550,8 +554,8 @@ class IcingSearchEngine {
       InitializeStatsProto* initialize_stats)
       ICING_EXCLUSIVE_LOCKS_REQUIRED(mutex_);
 
-  // Do any initialization/recovery necessary to create a DocumentStore
-  // instance.
+  // Do any initialization/recovery necessary to create term index, integer
+  // index, and qualified id join index instances.
   //
   // Returns:
   //   OK on success
@@ -640,9 +644,10 @@ class IcingSearchEngine {
       OptimizeStatsProto* optimize_stats)
       ICING_EXCLUSIVE_LOCKS_REQUIRED(mutex_);
 
-  // Helper method to restore missing document data in index_. All documents
-  // will be reindexed. This does not clear the index, so it is recommended to
-  // call Index::Reset first.
+  // Helper method to restore missing document data in index_, integer_index_,
+  // and qualified_id_join_index_. All documents will be reindexed. This does
+  // not clear the index, so it is recommended to call ClearAllIndices,
+  // ClearSearchIndices, or ClearJoinIndices first if needed.
   //
   // Returns:
   //   On success, OK and a bool indicating whether or not restoration was
@@ -657,6 +662,7 @@ class IcingSearchEngine {
     libtextclassifier3::Status status;
     bool index_needed_restoration;
     bool integer_index_needed_restoration;
+    bool qualified_id_join_index_needed_restoration;
   };
   IndexRestorationResult RestoreIndexIfNeeded()
       ICING_EXCLUSIVE_LOCKS_REQUIRED(mutex_);
@@ -674,13 +680,18 @@ class IcingSearchEngine {
       ICING_EXCLUSIVE_LOCKS_REQUIRED(mutex_);
 
   // Helper method to create all types of data indexing handlers to index term,
-  // integer, and joinable qualified ids.
+  // integer, and join qualified ids.
   libtextclassifier3::StatusOr<
       std::vector<std::unique_ptr<DataIndexingHandler>>>
   CreateDataIndexingHandlers() ICING_EXCLUSIVE_LOCKS_REQUIRED(mutex_);
 
-  // Helper method to discard parts of (term, integer) indices if they contain
-  // data for document ids greater than last_stored_document_id.
+  // Helper method to discard parts of (term, integer, qualified id join)
+  // indices if they contain data for document ids greater than
+  // last_stored_document_id.
+  //
+  // REQUIRES: last_stored_document_id is valid (!= kInvalidDocumentId). Note:
+  //   if we want to truncate everything in the index, then please call
+  //   ClearSearchIndices/ClearJoinIndices/ClearAllIndices instead.
   //
   // Returns:
   //   On success, a DocumentId indicating the first document to start for
@@ -691,25 +702,45 @@ class IcingSearchEngine {
     DocumentId first_document_to_reindex;
     bool index_needed_restoration;
     bool integer_index_needed_restoration;
+    bool qualified_id_join_index_needed_restoration;
 
-    explicit TruncateIndexResult(DocumentId first_document_to_reindex_in,
-                                 bool index_needed_restoration_in,
-                                 bool integer_index_needed_restoration_in)
+    explicit TruncateIndexResult(
+        DocumentId first_document_to_reindex_in,
+        bool index_needed_restoration_in,
+        bool integer_index_needed_restoration_in,
+        bool qualified_id_join_index_needed_restoration_in)
         : first_document_to_reindex(first_document_to_reindex_in),
           index_needed_restoration(index_needed_restoration_in),
-          integer_index_needed_restoration(
-              integer_index_needed_restoration_in) {}
+          integer_index_needed_restoration(integer_index_needed_restoration_in),
+          qualified_id_join_index_needed_restoration(
+              qualified_id_join_index_needed_restoration_in) {}
   };
   libtextclassifier3::StatusOr<TruncateIndexResult> TruncateIndicesTo(
       DocumentId last_stored_document_id)
       ICING_EXCLUSIVE_LOCKS_REQUIRED(mutex_);
 
-  // Helper method to discard the entire (term, integer) indices.
+  // Helper method to discard search (term, integer) indices.
+  //
+  // Returns:
+  //   OK on success
+  //   INTERNAL_ERROR on any I/O errors
+  libtextclassifier3::Status ClearSearchIndices()
+      ICING_EXCLUSIVE_LOCKS_REQUIRED(mutex_);
+
+  // Helper method to discard join (qualified id) indices.
+  //
+  // Returns:
+  //   OK on success
+  //   INTERNAL_ERROR on any I/O errors
+  libtextclassifier3::Status ClearJoinIndices()
+      ICING_EXCLUSIVE_LOCKS_REQUIRED(mutex_);
+
+  // Helper method to discard all search and join indices.
   //
   // Returns:
   //   OK on success
   //   INTERNAL_ERROR on any I/O errors
-  libtextclassifier3::Status ClearIndices()
+  libtextclassifier3::Status ClearAllIndices()
       ICING_EXCLUSIVE_LOCKS_REQUIRED(mutex_);
 };
 
diff --git a/icing/icing-search-engine_initialization_test.cc b/icing/icing-search-engine_initialization_test.cc
index f51abdf..6ba1737 100644
--- a/icing/icing-search-engine_initialization_test.cc
+++ b/icing/icing-search-engine_initialization_test.cc
@@ -28,6 +28,9 @@
 #include "icing/index/index.h"
 #include "icing/index/numeric/integer-index.h"
 #include "icing/jni/jni-cache.h"
+#include "icing/join/doc-join-info.h"
+#include "icing/join/join-processor.h"
+#include "icing/join/qualified-id-type-joinable-index.h"
 #include "icing/legacy/index/icing-mock-filesystem.h"
 #include "icing/portable/endian.h"
 #include "icing/portable/equals-proto.h"
@@ -66,10 +69,12 @@ namespace {
 
 using ::icing::lib::portable_equals_proto::EqualsProto;
 using ::testing::_;
+using ::testing::AtLeast;
 using ::testing::DoDefault;
 using ::testing::EndsWith;
 using ::testing::Eq;
 using ::testing::HasSubstr;
+using ::testing::IsEmpty;
 using ::testing::Matcher;
 using ::testing::Return;
 using ::testing::SizeIs;
@@ -162,6 +167,10 @@ std::string GetIntegerIndexDir() {
   return GetTestBaseDir() + "/integer_index_dir";
 }
 
+std::string GetQualifiedIdJoinIndexDir() {
+  return GetTestBaseDir() + "/qualified_id_join_index_dir";
+}
+
 std::string GetSchemaDir() { return GetTestBaseDir() + "/schema_dir"; }
 
 std::string GetHeaderFilename() {
@@ -239,6 +248,10 @@ ScoringSpecProto GetDefaultScoringSpec() {
   return scoring_spec;
 }
 
+// TODO(b/272145329): create SearchSpecBuilder, JoinSpecBuilder,
+// SearchResultProtoBuilder and ResultProtoBuilder for unit tests and build all
+// instances by them.
+
 TEST_F(IcingSearchEngineInitializationTest, UninitializedInstanceFailsSafely) {
   IcingSearchEngine icing(GetDefaultIcingOptions(), GetTestJniCache());
 
@@ -876,21 +889,73 @@ TEST_F(IcingSearchEngineInitializationTest,
 
 TEST_F(IcingSearchEngineInitializationTest,
        RecoverFromInconsistentDocumentStore) {
-  // Test the following scenario: document store is ahead of term and integer
-  // index. IcingSearchEngine should be able to recover term index. Several
-  // additional behaviors are also tested:
+  // Test the following scenario: document store is ahead of term, integer and
+  // qualified id join index. IcingSearchEngine should be able to recover all
+  // indices. Several additional behaviors are also tested:
   // - Index directory handling:
   //   - Term index directory should be unaffected.
   //   - Integer index directory should be unaffected.
+  //   - Qualified id join index directory should be unaffected.
   // - Truncate indices:
   //   - "TruncateTo()" for term index shouldn't take effect.
   //   - "Clear()" shouldn't be called for integer index, i.e. no integer index
   //     storage sub directories (path_expr = "*/integer_index_dir/*") should be
   //     discarded.
+  //   - "Clear()" shouldn't be called for qualified id join index, i.e. no
+  //     underlying storage sub directory (path_expr =
+  //     "*/qualified_id_join_index_dir/*") should be discarded.
   // - Still, we need to replay and reindex documents.
 
-  DocumentProto document1 = CreateMessageDocument("namespace", "uri1");
-  DocumentProto document2 = CreateMessageDocument("namespace", "uri2");
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("Person").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("name")
+                  .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("Message")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("body")
+                                        .SetDataTypeString(TERM_MATCH_PREFIX,
+                                                           TOKENIZER_PLAIN)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("indexableInteger")
+                                        .SetDataTypeInt64(NUMERIC_MATCH_RANGE)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("senderQualifiedId")
+                                        .SetDataTypeJoinableString(
+                                            JOINABLE_VALUE_TYPE_QUALIFIED_ID)
+                                        .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
+  DocumentProto person =
+      DocumentBuilder()
+          .SetKey("namespace", "person")
+          .SetSchema("Person")
+          .AddStringProperty("name", "person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto message1 =
+      DocumentBuilder()
+          .SetKey("namespace", "message/1")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body one")
+          .AddInt64Property("indexableInteger", 123)
+          .AddStringProperty("senderQualifiedId", "namespace#person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto message2 =
+      DocumentBuilder()
+          .SetKey("namespace", "message/2")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body two")
+          .AddInt64Property("indexableInteger", 123)
+          .AddStringProperty("senderQualifiedId", "namespace#person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
 
   {
     // Initializes folder and schema, index one document
@@ -899,8 +964,9 @@ TEST_F(IcingSearchEngineInitializationTest,
         std::make_unique<IcingFilesystem>(), std::make_unique<FakeClock>(),
         GetTestJniCache());
     EXPECT_THAT(icing.Initialize().status(), ProtoIsOk());
-    EXPECT_THAT(icing.SetSchema(CreateMessageSchema()).status(), ProtoIsOk());
-    EXPECT_THAT(icing.Put(document1).status(), ProtoIsOk());
+    EXPECT_THAT(icing.SetSchema(schema).status(), ProtoIsOk());
+    EXPECT_THAT(icing.Put(person).status(), ProtoIsOk());
+    EXPECT_THAT(icing.Put(message1).status(), ProtoIsOk());
   }  // This should shut down IcingSearchEngine and persist anything it needs to
 
   {
@@ -910,7 +976,7 @@ TEST_F(IcingSearchEngineInitializationTest,
         SchemaStore::Create(filesystem(), GetSchemaDir(), &fake_clock));
     ICING_EXPECT_OK(schema_store->SetSchema(CreateMessageSchema()));
 
-    // Puts a second document into DocumentStore but doesn't index it.
+    // Puts message2 into DocumentStore but doesn't index it.
     ICING_ASSERT_OK_AND_ASSIGN(
         DocumentStore::CreateResult create_result,
         DocumentStore::Create(filesystem(), GetDocumentDir(), &fake_clock,
@@ -918,11 +984,10 @@ TEST_F(IcingSearchEngineInitializationTest,
     std::unique_ptr<DocumentStore> document_store =
         std::move(create_result.document_store);
 
-    ICING_EXPECT_OK(document_store->Put(document2));
+    ICING_EXPECT_OK(document_store->Put(message2));
   }
 
-  // Mock filesystem to observe and check the behavior of term index and
-  // integer index.
+  // Mock filesystem to observe and check the behavior of all indices.
   auto mock_filesystem = std::make_unique<MockFilesystem>();
   EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(_))
       .WillRepeatedly(DoDefault());
@@ -939,6 +1004,15 @@ TEST_F(IcingSearchEngineInitializationTest,
   EXPECT_CALL(*mock_filesystem,
               DeleteDirectoryRecursively(HasSubstr("/integer_index_dir/")))
       .Times(0);
+  // Ensure qualified id join index directory should never be discarded, and
+  // Clear() should never be called (i.e. storage sub directory
+  // "*/qualified_id_join_index_dir/*" should never be discarded).
+  EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(
+                                    EndsWith("/qualified_id_join_index_dir")))
+      .Times(0);
+  EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(
+                                    HasSubstr("/qualified_id_join_index_dir/")))
+      .Times(0);
 
   TestIcingSearchEngine icing(GetDefaultIcingOptions(),
                               std::move(mock_filesystem),
@@ -953,27 +1027,30 @@ TEST_F(IcingSearchEngineInitializationTest,
   EXPECT_THAT(
       initialize_result.initialize_stats().integer_index_restoration_cause(),
       Eq(InitializeStatsProto::INCONSISTENT_WITH_GROUND_TRUTH));
+  EXPECT_THAT(initialize_result.initialize_stats()
+                  .qualified_id_join_index_restoration_cause(),
+              Eq(InitializeStatsProto::INCONSISTENT_WITH_GROUND_TRUTH));
 
   GetResultProto expected_get_result_proto;
   expected_get_result_proto.mutable_status()->set_code(StatusProto::OK);
-  *expected_get_result_proto.mutable_document() = document1;
+  *expected_get_result_proto.mutable_document() = message1;
 
   // DocumentStore kept the additional document
-  EXPECT_THAT(
-      icing.Get("namespace", "uri1", GetResultSpecProto::default_instance()),
-      EqualsProto(expected_get_result_proto));
+  EXPECT_THAT(icing.Get("namespace", "message/1",
+                        GetResultSpecProto::default_instance()),
+              EqualsProto(expected_get_result_proto));
 
-  *expected_get_result_proto.mutable_document() = document2;
-  EXPECT_THAT(
-      icing.Get("namespace", "uri2", GetResultSpecProto::default_instance()),
-      EqualsProto(expected_get_result_proto));
+  *expected_get_result_proto.mutable_document() = message2;
+  EXPECT_THAT(icing.Get("namespace", "message/2",
+                        GetResultSpecProto::default_instance()),
+              EqualsProto(expected_get_result_proto));
 
   SearchResultProto expected_search_result_proto;
   expected_search_result_proto.mutable_status()->set_code(StatusProto::OK);
   *expected_search_result_proto.mutable_results()->Add()->mutable_document() =
-      document2;
+      message2;
   *expected_search_result_proto.mutable_results()->Add()->mutable_document() =
-      document1;
+      message1;
 
   // We indexed the additional document in all indices.
   // Verify term search
@@ -998,6 +1075,40 @@ TEST_F(IcingSearchEngineInitializationTest,
                    ResultSpecProto::default_instance());
   EXPECT_THAT(search_result_google::protobuf, EqualsSearchResultIgnoreStatsAndScores(
                                         expected_search_result_proto));
+
+  // Verify join search: join a query for `name:person` with a child query for
+  // `body:message` based on the child's `senderQualifiedId` field.
+  SearchSpecProto search_spec3;
+  search_spec3.set_term_match_type(TermMatchType::EXACT_ONLY);
+  search_spec3.set_query("name:person");
+  JoinSpecProto* join_spec = search_spec3.mutable_join_spec();
+  join_spec->set_max_joined_child_count(100);
+  join_spec->set_parent_property_expression(
+      std::string(JoinProcessor::kQualifiedIdExpr));
+  join_spec->set_child_property_expression("senderQualifiedId");
+  join_spec->set_aggregation_scoring_strategy(
+      JoinSpecProto::AggregationScoringStrategy::COUNT);
+  JoinSpecProto::NestedSpecProto* nested_spec =
+      join_spec->mutable_nested_spec();
+  SearchSpecProto* nested_search_spec = nested_spec->mutable_search_spec();
+  nested_search_spec->set_term_match_type(TermMatchType::EXACT_ONLY);
+  nested_search_spec->set_query("body:message");
+  *nested_spec->mutable_scoring_spec() = GetDefaultScoringSpec();
+  *nested_spec->mutable_result_spec() = ResultSpecProto::default_instance();
+
+  SearchResultProto expected_join_search_result_proto;
+  expected_join_search_result_proto.mutable_status()->set_code(StatusProto::OK);
+  SearchResultProto::ResultProto* result_proto =
+      expected_join_search_result_proto.mutable_results()->Add();
+  *result_proto->mutable_document() = person;
+  *result_proto->mutable_joined_results()->Add()->mutable_document() = message2;
+  *result_proto->mutable_joined_results()->Add()->mutable_document() = message1;
+
+  SearchResultProto search_result_proto3 =
+      icing.Search(search_spec3, ScoringSpecProto::default_instance(),
+                   ResultSpecProto::default_instance());
+  EXPECT_THAT(search_result_proto3, EqualsSearchResultIgnoreStatsAndScores(
+                                        expected_join_search_result_proto));
 }
 
 TEST_F(IcingSearchEngineInitializationTest, RecoverFromCorruptIndex) {
@@ -1008,20 +1119,67 @@ TEST_F(IcingSearchEngineInitializationTest, RecoverFromCorruptIndex) {
   //   - Should discard the entire term index directory and start it from
   //     scratch.
   //   - Integer index directory should be unaffected.
+  //   - Qualified id join index directory should be unaffected.
   // - Truncate indices:
   //   - "TruncateTo()" for term index shouldn't take effect since we start it
   //     from scratch.
   //   - "Clear()" shouldn't be called for integer index, i.e. no integer index
   //     storage sub directories (path_expr = "*/integer_index_dir/*") should be
   //     discarded.
+  //   - "Clear()" shouldn't be called for qualified id join index, i.e. no
+  //     underlying storage sub directory (path_expr =
+  //     "*/qualified_id_join_index_dir/*") should be discarded.
+
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("Person").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("name")
+                  .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("Message")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("body")
+                                        .SetDataTypeString(TERM_MATCH_PREFIX,
+                                                           TOKENIZER_PLAIN)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("indexableInteger")
+                                        .SetDataTypeInt64(NUMERIC_MATCH_RANGE)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("senderQualifiedId")
+                                        .SetDataTypeJoinableString(
+                                            JOINABLE_VALUE_TYPE_QUALIFIED_ID)
+                                        .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
+  DocumentProto person =
+      DocumentBuilder()
+          .SetKey("namespace", "person")
+          .SetSchema("Person")
+          .AddStringProperty("name", "person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto message =
+      DocumentBuilder()
+          .SetKey("namespace", "message/1")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body")
+          .AddInt64Property("indexableInteger", 123)
+          .AddStringProperty("senderQualifiedId", "namespace#person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+
   SearchSpecProto search_spec;
-  search_spec.set_query("message");
+  search_spec.set_query("body:message");
   search_spec.set_term_match_type(TermMatchType::EXACT_ONLY);
 
   SearchResultProto expected_search_result_proto;
   expected_search_result_proto.mutable_status()->set_code(StatusProto::OK);
   *expected_search_result_proto.mutable_results()->Add()->mutable_document() =
-      CreateMessageDocument("namespace", "uri");
+      message;
 
   {
     // Initializes folder and schema, index one document
@@ -1030,9 +1188,9 @@ TEST_F(IcingSearchEngineInitializationTest, RecoverFromCorruptIndex) {
         std::make_unique<IcingFilesystem>(), std::make_unique<FakeClock>(),
         GetTestJniCache());
     EXPECT_THAT(icing.Initialize().status(), ProtoIsOk());
-    EXPECT_THAT(icing.SetSchema(CreateMessageSchema()).status(), ProtoIsOk());
-    EXPECT_THAT(icing.Put(CreateMessageDocument("namespace", "uri")).status(),
-                ProtoIsOk());
+    EXPECT_THAT(icing.SetSchema(schema).status(), ProtoIsOk());
+    EXPECT_THAT(icing.Put(person).status(), ProtoIsOk());
+    EXPECT_THAT(icing.Put(message).status(), ProtoIsOk());
     SearchResultProto search_result_proto =
         icing.Search(search_spec, GetDefaultScoringSpec(),
                      ResultSpecProto::default_instance());
@@ -1048,8 +1206,7 @@ TEST_F(IcingSearchEngineInitializationTest, RecoverFromCorruptIndex) {
     ASSERT_TRUE(filesystem()->Write(fd.get(), "1234", 4));
   }
 
-  // Mock filesystem to observe and check the behavior of term index and integer
-  // index.
+  // Mock filesystem to observe and check the behavior of all indices.
   auto mock_filesystem = std::make_unique<MockFilesystem>();
   EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(_))
       .WillRepeatedly(DoDefault());
@@ -1066,6 +1223,15 @@ TEST_F(IcingSearchEngineInitializationTest, RecoverFromCorruptIndex) {
   EXPECT_CALL(*mock_filesystem,
               DeleteDirectoryRecursively(HasSubstr("/integer_index_dir/")))
       .Times(0);
+  // Ensure qualified id join index directory should never be discarded, and
+  // Clear() should never be called (i.e. storage sub directory
+  // "*/qualified_id_join_index_dir/*" should never be discarded).
+  EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(
+                                    EndsWith("/qualified_id_join_index_dir")))
+      .Times(0);
+  EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(
+                                    HasSubstr("/qualified_id_join_index_dir/")))
+      .Times(0);
 
   TestIcingSearchEngine icing(GetDefaultIcingOptions(),
                               std::move(mock_filesystem),
@@ -1078,6 +1244,9 @@ TEST_F(IcingSearchEngineInitializationTest, RecoverFromCorruptIndex) {
   EXPECT_THAT(
       initialize_result.initialize_stats().integer_index_restoration_cause(),
       Eq(InitializeStatsProto::NONE));
+  EXPECT_THAT(initialize_result.initialize_stats()
+                  .qualified_id_join_index_restoration_cause(),
+              Eq(InitializeStatsProto::NONE));
 
   // Check that our index is ok by searching over the restored index
   SearchResultProto search_result_proto =
@@ -1095,11 +1264,58 @@ TEST_F(IcingSearchEngineInitializationTest, RecoverFromCorruptIntegerIndex) {
   //   - Term index directory should be unaffected.
   //   - Should discard the entire integer index directory and start it from
   //     scratch.
+  //   - Qualified id join index directory should be unaffected.
   // - Truncate indices:
   //   - "TruncateTo()" for term index shouldn't take effect.
   //   - "Clear()" shouldn't be called for integer index, i.e. no integer index
   //     storage sub directories (path_expr = "*/integer_index_dir/*") should be
   //     discarded, since we start it from scratch.
+  //   - "Clear()" shouldn't be called for qualified id join index, i.e. no
+  //     underlying storage sub directory (path_expr =
+  //     "*/qualified_id_join_index_dir/*") should be discarded.
+
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("Person").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("name")
+                  .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("Message")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("body")
+                                        .SetDataTypeString(TERM_MATCH_PREFIX,
+                                                           TOKENIZER_PLAIN)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("indexableInteger")
+                                        .SetDataTypeInt64(NUMERIC_MATCH_RANGE)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("senderQualifiedId")
+                                        .SetDataTypeJoinableString(
+                                            JOINABLE_VALUE_TYPE_QUALIFIED_ID)
+                                        .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
+  DocumentProto person =
+      DocumentBuilder()
+          .SetKey("namespace", "person")
+          .SetSchema("Person")
+          .AddStringProperty("name", "person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto message =
+      DocumentBuilder()
+          .SetKey("namespace", "message/1")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body")
+          .AddInt64Property("indexableInteger", 123)
+          .AddStringProperty("senderQualifiedId", "namespace#person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+
   SearchSpecProto search_spec;
   search_spec.set_query("indexableInteger == 123");
   search_spec.set_search_type(
@@ -1109,7 +1325,7 @@ TEST_F(IcingSearchEngineInitializationTest, RecoverFromCorruptIntegerIndex) {
   SearchResultProto expected_search_result_proto;
   expected_search_result_proto.mutable_status()->set_code(StatusProto::OK);
   *expected_search_result_proto.mutable_results()->Add()->mutable_document() =
-      CreateMessageDocument("namespace", "uri");
+      message;
 
   {
     // Initializes folder and schema, index one document
@@ -1118,9 +1334,9 @@ TEST_F(IcingSearchEngineInitializationTest, RecoverFromCorruptIntegerIndex) {
         std::make_unique<IcingFilesystem>(), std::make_unique<FakeClock>(),
         GetTestJniCache());
     EXPECT_THAT(icing.Initialize().status(), ProtoIsOk());
-    EXPECT_THAT(icing.SetSchema(CreateMessageSchema()).status(), ProtoIsOk());
-    EXPECT_THAT(icing.Put(CreateMessageDocument("namespace", "uri")).status(),
-                ProtoIsOk());
+    EXPECT_THAT(icing.SetSchema(schema).status(), ProtoIsOk());
+    EXPECT_THAT(icing.Put(person).status(), ProtoIsOk());
+    EXPECT_THAT(icing.Put(message).status(), ProtoIsOk());
     SearchResultProto search_result_proto =
         icing.Search(search_spec, GetDefaultScoringSpec(),
                      ResultSpecProto::default_instance());
@@ -1138,8 +1354,7 @@ TEST_F(IcingSearchEngineInitializationTest, RecoverFromCorruptIntegerIndex) {
     ASSERT_TRUE(filesystem()->Write(fd.get(), "1234", 4));
   }
 
-  // Mock filesystem to observe and check the behavior of term index and integer
-  // index.
+  // Mock filesystem to observe and check the behavior of all indices.
   auto mock_filesystem = std::make_unique<MockFilesystem>();
   EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(_))
       .WillRepeatedly(DoDefault());
@@ -1156,6 +1371,15 @@ TEST_F(IcingSearchEngineInitializationTest, RecoverFromCorruptIntegerIndex) {
   EXPECT_CALL(*mock_filesystem,
               DeleteDirectoryRecursively(HasSubstr("/integer_index_dir/")))
       .Times(0);
+  // Ensure qualified id join index directory should never be discarded, and
+  // Clear() should never be called (i.e. storage sub directory
+  // "*/qualified_id_join_index_dir/*" should never be discarded).
+  EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(
+                                    EndsWith("/qualified_id_join_index_dir")))
+      .Times(0);
+  EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(
+                                    HasSubstr("/qualified_id_join_index_dir/")))
+      .Times(0);
 
   TestIcingSearchEngine icing(GetDefaultIcingOptions(),
                               std::move(mock_filesystem),
@@ -1168,6 +1392,175 @@ TEST_F(IcingSearchEngineInitializationTest, RecoverFromCorruptIntegerIndex) {
   EXPECT_THAT(
       initialize_result.initialize_stats().integer_index_restoration_cause(),
       Eq(InitializeStatsProto::IO_ERROR));
+  EXPECT_THAT(initialize_result.initialize_stats()
+                  .qualified_id_join_index_restoration_cause(),
+              Eq(InitializeStatsProto::NONE));
+
+  // Check that our index is ok by searching over the restored index
+  SearchResultProto search_result_proto =
+      icing.Search(search_spec, GetDefaultScoringSpec(),
+                   ResultSpecProto::default_instance());
+  EXPECT_THAT(search_result_proto, EqualsSearchResultIgnoreStatsAndScores(
+                                       expected_search_result_proto));
+}
+
+TEST_F(IcingSearchEngineInitializationTest,
+       RecoverFromCorruptQualifiedIdJoinIndex) {
+  // Test the following scenario: qualified id join index is corrupted (e.g.
+  // checksum doesn't match). IcingSearchEngine should be able to recover
+  // qualified id join index. Several additional behaviors are also tested:
+  // - Index directory handling:
+  //   - Term index directory should be unaffected.
+  //   - Integer index directory should be unaffected.
+  //   - Should discard the entire qualified id join index directory and start
+  //     it from scratch.
+  // - Truncate indices:
+  //   - "TruncateTo()" for term index shouldn't take effect.
+  //   - "Clear()" shouldn't be called for integer index, i.e. no integer index
+  //     storage sub directories (path_expr = "*/integer_index_dir/*") should be
+  //     discarded.
+  //   - "Clear()" shouldn't be called for qualified id join index, i.e. no
+  //     underlying storage sub directory (path_expr =
+  //     "*/qualified_id_join_index_dir/*") should be discarded, since we start
+  //     it from scratch.
+
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("Person").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("name")
+                  .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("Message")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("body")
+                                        .SetDataTypeString(TERM_MATCH_PREFIX,
+                                                           TOKENIZER_PLAIN)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("indexableInteger")
+                                        .SetDataTypeInt64(NUMERIC_MATCH_RANGE)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("senderQualifiedId")
+                                        .SetDataTypeJoinableString(
+                                            JOINABLE_VALUE_TYPE_QUALIFIED_ID)
+                                        .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
+  DocumentProto person =
+      DocumentBuilder()
+          .SetKey("namespace", "person")
+          .SetSchema("Person")
+          .AddStringProperty("name", "person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto message =
+      DocumentBuilder()
+          .SetKey("namespace", "message/1")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body")
+          .AddInt64Property("indexableInteger", 123)
+          .AddStringProperty("senderQualifiedId", "namespace#person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+
+  // Prepare join search spec to join a query for `name:person` with a child
+  // query for `body:message` based on the child's `senderQualifiedId` field.
+  SearchSpecProto search_spec;
+  search_spec.set_term_match_type(TermMatchType::EXACT_ONLY);
+  search_spec.set_query("name:person");
+  JoinSpecProto* join_spec = search_spec.mutable_join_spec();
+  join_spec->set_max_joined_child_count(100);
+  join_spec->set_parent_property_expression(
+      std::string(JoinProcessor::kQualifiedIdExpr));
+  join_spec->set_child_property_expression("senderQualifiedId");
+  join_spec->set_aggregation_scoring_strategy(
+      JoinSpecProto::AggregationScoringStrategy::COUNT);
+  JoinSpecProto::NestedSpecProto* nested_spec =
+      join_spec->mutable_nested_spec();
+  SearchSpecProto* nested_search_spec = nested_spec->mutable_search_spec();
+  nested_search_spec->set_term_match_type(TermMatchType::EXACT_ONLY);
+  nested_search_spec->set_query("body:message");
+  *nested_spec->mutable_scoring_spec() = GetDefaultScoringSpec();
+  *nested_spec->mutable_result_spec() = ResultSpecProto::default_instance();
+
+  SearchResultProto expected_search_result_proto;
+  expected_search_result_proto.mutable_status()->set_code(StatusProto::OK);
+  SearchResultProto::ResultProto* result_proto =
+      expected_search_result_proto.mutable_results()->Add();
+  *result_proto->mutable_document() = person;
+  *result_proto->mutable_joined_results()->Add()->mutable_document() = message;
+
+  {
+    // Initializes folder and schema, index one document
+    TestIcingSearchEngine icing(
+        GetDefaultIcingOptions(), std::make_unique<Filesystem>(),
+        std::make_unique<IcingFilesystem>(), std::make_unique<FakeClock>(),
+        GetTestJniCache());
+    EXPECT_THAT(icing.Initialize().status(), ProtoIsOk());
+    EXPECT_THAT(icing.SetSchema(schema).status(), ProtoIsOk());
+    EXPECT_THAT(icing.Put(person).status(), ProtoIsOk());
+    EXPECT_THAT(icing.Put(message).status(), ProtoIsOk());
+    SearchResultProto search_result_proto =
+        icing.Search(search_spec, GetDefaultScoringSpec(),
+                     ResultSpecProto::default_instance());
+    EXPECT_THAT(search_result_proto, EqualsSearchResultIgnoreStatsAndScores(
+                                         expected_search_result_proto));
+  }  // This should shut down IcingSearchEngine and persist anything it needs to
+
+  // Manually corrupt qualified id join index
+  {
+    const std::string qualified_id_join_index_metadata_file =
+        GetQualifiedIdJoinIndexDir() + "/metadata";
+    ScopedFd fd(filesystem()->OpenForWrite(
+        qualified_id_join_index_metadata_file.c_str()));
+    ASSERT_TRUE(fd.is_valid());
+    ASSERT_TRUE(filesystem()->Write(fd.get(), "1234", 4));
+  }
+
+  // Mock filesystem to observe and check the behavior of all indices.
+  auto mock_filesystem = std::make_unique<MockFilesystem>();
+  EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(_))
+      .WillRepeatedly(DoDefault());
+  // Ensure term index directory should never be discarded.
+  EXPECT_CALL(*mock_filesystem,
+              DeleteDirectoryRecursively(EndsWith("/index_dir")))
+      .Times(0);
+  // Ensure integer index directory should never be discarded, and Clear()
+  // should never be called (i.e. storage sub directory "*/integer_index_dir/*"
+  // should never be discarded).
+  EXPECT_CALL(*mock_filesystem,
+              DeleteDirectoryRecursively(EndsWith("/integer_index_dir")))
+      .Times(0);
+  EXPECT_CALL(*mock_filesystem,
+              DeleteDirectoryRecursively(HasSubstr("/integer_index_dir/")))
+      .Times(0);
+  // Ensure qualified id join index directory should be discarded once, and
+  // Clear() should never be called (i.e. storage sub directory
+  // "*/qualified_id_join_index_dir/*" should never be discarded).
+  EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(
+                                    EndsWith("/qualified_id_join_index_dir")))
+      .Times(1);
+  EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(
+                                    HasSubstr("/qualified_id_join_index_dir/")))
+      .Times(0);
+
+  TestIcingSearchEngine icing(GetDefaultIcingOptions(),
+                              std::move(mock_filesystem),
+                              std::make_unique<IcingFilesystem>(),
+                              std::make_unique<FakeClock>(), GetTestJniCache());
+  InitializeResultProto initialize_result = icing.Initialize();
+  EXPECT_THAT(initialize_result.status(), ProtoIsOk());
+  EXPECT_THAT(initialize_result.initialize_stats().index_restoration_cause(),
+              Eq(InitializeStatsProto::NONE));
+  EXPECT_THAT(
+      initialize_result.initialize_stats().integer_index_restoration_cause(),
+      Eq(InitializeStatsProto::NONE));
+  EXPECT_THAT(initialize_result.initialize_stats()
+                  .qualified_id_join_index_restoration_cause(),
+              Eq(InitializeStatsProto::IO_ERROR));
 
   // Check that our index is ok by searching over the restored index
   SearchResultProto search_result_proto =
@@ -1185,19 +1578,60 @@ TEST_F(IcingSearchEngineInitializationTest, RestoreIndexLoseTermIndex) {
   //   - Term index directory should not be discarded since we've already lost
   //     it. Start it from scratch.
   //   - Integer index directory should be unaffected.
+  //   - Qualified id join index directory should be unaffected.
   // - Truncate indices:
   //   - "TruncateTo()" for term index shouldn't take effect since we start it
   //     from scratch.
   //   - "Clear()" shouldn't be called for integer index, i.e. no integer index
   //     storage sub directories (path_expr = "*/integer_index_dir/*") should be
   //     discarded.
-  DocumentProto document = DocumentBuilder()
-                               .SetKey("icing", "fake_type/0")
-                               .SetSchema("Message")
-                               .AddStringProperty("body", kIpsumText)
-                               .AddInt64Property("indexableInteger", 123)
-                               .Build();
-  // 1. Create an index with 3 documents.
+  //   - "Clear()" shouldn't be called for qualified id join index, i.e. no
+  //     underlying storage sub directory (path_expr =
+  //     "*/qualified_id_join_index_dir/*") should be discarded.
+
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("Person").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("name")
+                  .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("Message")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("body")
+                                        .SetDataTypeString(TERM_MATCH_PREFIX,
+                                                           TOKENIZER_PLAIN)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("indexableInteger")
+                                        .SetDataTypeInt64(NUMERIC_MATCH_RANGE)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("senderQualifiedId")
+                                        .SetDataTypeJoinableString(
+                                            JOINABLE_VALUE_TYPE_QUALIFIED_ID)
+                                        .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
+  DocumentProto person =
+      DocumentBuilder()
+          .SetKey("namespace", "person")
+          .SetSchema("Person")
+          .AddStringProperty("name", "person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto message =
+      DocumentBuilder()
+          .SetKey("namespace", "message/1")
+          .SetSchema("Message")
+          .AddStringProperty("body", kIpsumText)
+          .AddInt64Property("indexableInteger", 123)
+          .AddStringProperty("senderQualifiedId", "namespace#person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+
+  // 1. Create an index with 3 message documents.
   {
     TestIcingSearchEngine icing(
         GetDefaultIcingOptions(), std::make_unique<Filesystem>(),
@@ -1205,13 +1639,14 @@ TEST_F(IcingSearchEngineInitializationTest, RestoreIndexLoseTermIndex) {
         GetTestJniCache());
 
     ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
-    ASSERT_THAT(icing.SetSchema(CreateMessageSchema()).status(), ProtoIsOk());
+    ASSERT_THAT(icing.SetSchema(schema).status(), ProtoIsOk());
 
-    EXPECT_THAT(icing.Put(document).status(), ProtoIsOk());
-    document = DocumentBuilder(document).SetUri("fake_type/1").Build();
-    EXPECT_THAT(icing.Put(document).status(), ProtoIsOk());
-    document = DocumentBuilder(document).SetUri("fake_type/2").Build();
-    EXPECT_THAT(icing.Put(document).status(), ProtoIsOk());
+    EXPECT_THAT(icing.Put(person).status(), ProtoIsOk());
+    EXPECT_THAT(icing.Put(message).status(), ProtoIsOk());
+    message = DocumentBuilder(message).SetUri("message/2").Build();
+    EXPECT_THAT(icing.Put(message).status(), ProtoIsOk());
+    message = DocumentBuilder(message).SetUri("message/3").Build();
+    EXPECT_THAT(icing.Put(message).status(), ProtoIsOk());
   }
 
   // 2. Delete the term index directory to trigger RestoreIndexIfNeeded.
@@ -1220,8 +1655,7 @@ TEST_F(IcingSearchEngineInitializationTest, RestoreIndexLoseTermIndex) {
 
   // 3. Create the index again. This should trigger index restoration.
   {
-    // Mock filesystem to observe and check the behavior of term index and
-    // integer index.
+    // Mock filesystem to observe and check the behavior of all indices.
     auto mock_filesystem = std::make_unique<MockFilesystem>();
     EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(_))
         .WillRepeatedly(DoDefault());
@@ -1239,6 +1673,16 @@ TEST_F(IcingSearchEngineInitializationTest, RestoreIndexLoseTermIndex) {
     EXPECT_CALL(*mock_filesystem,
                 DeleteDirectoryRecursively(HasSubstr("/integer_index_dir/")))
         .Times(0);
+    // Ensure qualified id join index directory should never be discarded, and
+    // Clear() should never be called (i.e. storage sub directory
+    // "*/qualified_id_join_index_dir/*" should never be discarded).
+    EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(
+                                      EndsWith("/qualified_id_join_index_dir")))
+        .Times(0);
+    EXPECT_CALL(
+        *mock_filesystem,
+        DeleteDirectoryRecursively(HasSubstr("/qualified_id_join_index_dir/")))
+        .Times(0);
 
     TestIcingSearchEngine icing(
         GetDefaultIcingOptions(), std::move(mock_filesystem),
@@ -1251,10 +1695,13 @@ TEST_F(IcingSearchEngineInitializationTest, RestoreIndexLoseTermIndex) {
     EXPECT_THAT(
         initialize_result.initialize_stats().integer_index_restoration_cause(),
         Eq(InitializeStatsProto::NONE));
+    EXPECT_THAT(initialize_result.initialize_stats()
+                    .qualified_id_join_index_restoration_cause(),
+                Eq(InitializeStatsProto::NONE));
 
     // Verify term index works normally
     SearchSpecProto search_spec1;
-    search_spec1.set_query("consectetur");
+    search_spec1.set_query("body:consectetur");
     search_spec1.set_term_match_type(TermMatchType::EXACT_ONLY);
     SearchResultProto results1 =
         icing.Search(search_spec1, ScoringSpecProto::default_instance(),
@@ -1263,9 +1710,9 @@ TEST_F(IcingSearchEngineInitializationTest, RestoreIndexLoseTermIndex) {
     EXPECT_THAT(results1.next_page_token(), Eq(0));
     // All documents should be retrievable.
     ASSERT_THAT(results1.results(), SizeIs(3));
-    EXPECT_THAT(results1.results(0).document().uri(), Eq("fake_type/2"));
-    EXPECT_THAT(results1.results(1).document().uri(), Eq("fake_type/1"));
-    EXPECT_THAT(results1.results(2).document().uri(), Eq("fake_type/0"));
+    EXPECT_THAT(results1.results(0).document().uri(), Eq("message/3"));
+    EXPECT_THAT(results1.results(1).document().uri(), Eq("message/2"));
+    EXPECT_THAT(results1.results(2).document().uri(), Eq("message/1"));
 
     // Verify integer index works normally
     SearchSpecProto search_spec2;
@@ -1278,9 +1725,43 @@ TEST_F(IcingSearchEngineInitializationTest, RestoreIndexLoseTermIndex) {
         icing.Search(search_spec2, ScoringSpecProto::default_instance(),
                      ResultSpecProto::default_instance());
     ASSERT_THAT(results2.results(), SizeIs(3));
-    EXPECT_THAT(results2.results(0).document().uri(), Eq("fake_type/2"));
-    EXPECT_THAT(results2.results(1).document().uri(), Eq("fake_type/1"));
-    EXPECT_THAT(results2.results(2).document().uri(), Eq("fake_type/0"));
+    EXPECT_THAT(results2.results(0).document().uri(), Eq("message/3"));
+    EXPECT_THAT(results2.results(1).document().uri(), Eq("message/2"));
+    EXPECT_THAT(results2.results(2).document().uri(), Eq("message/1"));
+
+    // Verify qualified id join index works normally: join a query for
+    // `name:person` with a child query for `body:consectetur` based on the
+    // child's `senderQualifiedId` field.
+    SearchSpecProto search_spec3;
+    search_spec3.set_term_match_type(TermMatchType::EXACT_ONLY);
+    search_spec3.set_query("name:person");
+    JoinSpecProto* join_spec = search_spec3.mutable_join_spec();
+    join_spec->set_max_joined_child_count(100);
+    join_spec->set_parent_property_expression(
+        std::string(JoinProcessor::kQualifiedIdExpr));
+    join_spec->set_child_property_expression("senderQualifiedId");
+    join_spec->set_aggregation_scoring_strategy(
+        JoinSpecProto::AggregationScoringStrategy::COUNT);
+    JoinSpecProto::NestedSpecProto* nested_spec =
+        join_spec->mutable_nested_spec();
+    SearchSpecProto* nested_search_spec = nested_spec->mutable_search_spec();
+    nested_search_spec->set_term_match_type(TermMatchType::EXACT_ONLY);
+    nested_search_spec->set_query("body:consectetur");
+    *nested_spec->mutable_scoring_spec() = GetDefaultScoringSpec();
+    *nested_spec->mutable_result_spec() = ResultSpecProto::default_instance();
+
+    SearchResultProto results3 =
+        icing.Search(search_spec3, ScoringSpecProto::default_instance(),
+                     ResultSpecProto::default_instance());
+    ASSERT_THAT(results3.results(), SizeIs(1));
+    EXPECT_THAT(results3.results(0).document().uri(), Eq("person"));
+    EXPECT_THAT(results3.results(0).joined_results(), SizeIs(3));
+    EXPECT_THAT(results3.results(0).joined_results(0).document().uri(),
+                Eq("message/3"));
+    EXPECT_THAT(results3.results(0).joined_results(1).document().uri(),
+                Eq("message/2"));
+    EXPECT_THAT(results3.results(0).joined_results(2).document().uri(),
+                Eq("message/1"));
   }
 }
 
@@ -1292,18 +1773,59 @@ TEST_F(IcingSearchEngineInitializationTest, RestoreIndexLoseIntegerIndex) {
   //   - Term index directory should be unaffected.
   //   - Integer index directory should not be discarded since we've already
   //     lost it. Start it from scratch.
+  //   - Qualified id join index directory should be unaffected.
   // - Truncate indices:
   //   - "TruncateTo()" for term index shouldn't take effect.
   //   - "Clear()" shouldn't be called for integer index, i.e. no integer index
   //     storage sub directories (path_expr = "*/integer_index_dir/*") should be
   //     discarded, since we start it from scratch.
-  DocumentProto document = DocumentBuilder()
-                               .SetKey("icing", "fake_type/0")
-                               .SetSchema("Message")
-                               .AddStringProperty("body", kIpsumText)
-                               .AddInt64Property("indexableInteger", 123)
-                               .Build();
-  // 1. Create an index with 3 documents.
+  //   - "Clear()" shouldn't be called for qualified id join index, i.e. no
+  //     underlying storage sub directory (path_expr =
+  //     "*/qualified_id_join_index_dir/*") should be discarded.
+
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("Person").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("name")
+                  .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("Message")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("body")
+                                        .SetDataTypeString(TERM_MATCH_PREFIX,
+                                                           TOKENIZER_PLAIN)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("indexableInteger")
+                                        .SetDataTypeInt64(NUMERIC_MATCH_RANGE)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("senderQualifiedId")
+                                        .SetDataTypeJoinableString(
+                                            JOINABLE_VALUE_TYPE_QUALIFIED_ID)
+                                        .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
+  DocumentProto person =
+      DocumentBuilder()
+          .SetKey("namespace", "person")
+          .SetSchema("Person")
+          .AddStringProperty("name", "person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto message =
+      DocumentBuilder()
+          .SetKey("namespace", "message/1")
+          .SetSchema("Message")
+          .AddStringProperty("body", kIpsumText)
+          .AddInt64Property("indexableInteger", 123)
+          .AddStringProperty("senderQualifiedId", "namespace#person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+
+  // 1. Create an index with 3 message documents.
   {
     TestIcingSearchEngine icing(
         GetDefaultIcingOptions(), std::make_unique<Filesystem>(),
@@ -1311,13 +1833,14 @@ TEST_F(IcingSearchEngineInitializationTest, RestoreIndexLoseIntegerIndex) {
         GetTestJniCache());
 
     ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
-    ASSERT_THAT(icing.SetSchema(CreateMessageSchema()).status(), ProtoIsOk());
+    ASSERT_THAT(icing.SetSchema(schema).status(), ProtoIsOk());
 
-    EXPECT_THAT(icing.Put(document).status(), ProtoIsOk());
-    document = DocumentBuilder(document).SetUri("fake_type/1").Build();
-    EXPECT_THAT(icing.Put(document).status(), ProtoIsOk());
-    document = DocumentBuilder(document).SetUri("fake_type/2").Build();
-    EXPECT_THAT(icing.Put(document).status(), ProtoIsOk());
+    EXPECT_THAT(icing.Put(person).status(), ProtoIsOk());
+    EXPECT_THAT(icing.Put(message).status(), ProtoIsOk());
+    message = DocumentBuilder(message).SetUri("message/2").Build();
+    EXPECT_THAT(icing.Put(message).status(), ProtoIsOk());
+    message = DocumentBuilder(message).SetUri("message/3").Build();
+    EXPECT_THAT(icing.Put(message).status(), ProtoIsOk());
   }
 
   // 2. Delete the integer index file to trigger RestoreIndexIfNeeded.
@@ -1326,8 +1849,7 @@ TEST_F(IcingSearchEngineInitializationTest, RestoreIndexLoseIntegerIndex) {
 
   // 3. Create the index again. This should trigger index restoration.
   {
-    // Mock filesystem to observe and check the behavior of term index and
-    // integer index.
+    // Mock filesystem to observe and check the behavior of all indices.
     auto mock_filesystem = std::make_unique<MockFilesystem>();
     EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(_))
         .WillRepeatedly(DoDefault());
@@ -1345,6 +1867,16 @@ TEST_F(IcingSearchEngineInitializationTest, RestoreIndexLoseIntegerIndex) {
     EXPECT_CALL(*mock_filesystem,
                 DeleteDirectoryRecursively(HasSubstr("/integer_index_dir/")))
         .Times(0);
+    // Ensure qualified id join index directory should never be discarded, and
+    // Clear() should never be called (i.e. storage sub directory
+    // "*/qualified_id_join_index_dir/*" should never be discarded).
+    EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(
+                                      EndsWith("/qualified_id_join_index_dir")))
+        .Times(0);
+    EXPECT_CALL(
+        *mock_filesystem,
+        DeleteDirectoryRecursively(HasSubstr("/qualified_id_join_index_dir/")))
+        .Times(0);
 
     TestIcingSearchEngine icing(
         GetDefaultIcingOptions(), std::move(mock_filesystem),
@@ -1357,10 +1889,13 @@ TEST_F(IcingSearchEngineInitializationTest, RestoreIndexLoseIntegerIndex) {
     EXPECT_THAT(
         initialize_result.initialize_stats().integer_index_restoration_cause(),
         Eq(InitializeStatsProto::INCONSISTENT_WITH_GROUND_TRUTH));
+    EXPECT_THAT(initialize_result.initialize_stats()
+                    .qualified_id_join_index_restoration_cause(),
+                Eq(InitializeStatsProto::NONE));
 
     // Verify term index works normally
     SearchSpecProto search_spec1;
-    search_spec1.set_query("consectetur");
+    search_spec1.set_query("body:consectetur");
     search_spec1.set_term_match_type(TermMatchType::EXACT_ONLY);
     SearchResultProto results1 =
         icing.Search(search_spec1, ScoringSpecProto::default_instance(),
@@ -1369,9 +1904,9 @@ TEST_F(IcingSearchEngineInitializationTest, RestoreIndexLoseIntegerIndex) {
     EXPECT_THAT(results1.next_page_token(), Eq(0));
     // All documents should be retrievable.
     ASSERT_THAT(results1.results(), SizeIs(3));
-    EXPECT_THAT(results1.results(0).document().uri(), Eq("fake_type/2"));
-    EXPECT_THAT(results1.results(1).document().uri(), Eq("fake_type/1"));
-    EXPECT_THAT(results1.results(2).document().uri(), Eq("fake_type/0"));
+    EXPECT_THAT(results1.results(0).document().uri(), Eq("message/3"));
+    EXPECT_THAT(results1.results(1).document().uri(), Eq("message/2"));
+    EXPECT_THAT(results1.results(2).document().uri(), Eq("message/1"));
 
     // Verify integer index works normally
     SearchSpecProto search_spec2;
@@ -1384,9 +1919,239 @@ TEST_F(IcingSearchEngineInitializationTest, RestoreIndexLoseIntegerIndex) {
         icing.Search(search_spec2, ScoringSpecProto::default_instance(),
                      ResultSpecProto::default_instance());
     ASSERT_THAT(results2.results(), SizeIs(3));
-    EXPECT_THAT(results2.results(0).document().uri(), Eq("fake_type/2"));
-    EXPECT_THAT(results2.results(1).document().uri(), Eq("fake_type/1"));
-    EXPECT_THAT(results2.results(2).document().uri(), Eq("fake_type/0"));
+    EXPECT_THAT(results2.results(0).document().uri(), Eq("message/3"));
+    EXPECT_THAT(results2.results(1).document().uri(), Eq("message/2"));
+    EXPECT_THAT(results2.results(2).document().uri(), Eq("message/1"));
+
+    // Verify qualified id join index works normally: join a query for
+    // `name:person` with a child query for `body:consectetur` based on the
+    // child's `senderQualifiedId` field.
+    SearchSpecProto search_spec3;
+    search_spec3.set_term_match_type(TermMatchType::EXACT_ONLY);
+    search_spec3.set_query("name:person");
+    JoinSpecProto* join_spec = search_spec3.mutable_join_spec();
+    join_spec->set_max_joined_child_count(100);
+    join_spec->set_parent_property_expression(
+        std::string(JoinProcessor::kQualifiedIdExpr));
+    join_spec->set_child_property_expression("senderQualifiedId");
+    join_spec->set_aggregation_scoring_strategy(
+        JoinSpecProto::AggregationScoringStrategy::COUNT);
+    JoinSpecProto::NestedSpecProto* nested_spec =
+        join_spec->mutable_nested_spec();
+    SearchSpecProto* nested_search_spec = nested_spec->mutable_search_spec();
+    nested_search_spec->set_term_match_type(TermMatchType::EXACT_ONLY);
+    nested_search_spec->set_query("body:consectetur");
+    *nested_spec->mutable_scoring_spec() = GetDefaultScoringSpec();
+    *nested_spec->mutable_result_spec() = ResultSpecProto::default_instance();
+
+    SearchResultProto results3 =
+        icing.Search(search_spec3, ScoringSpecProto::default_instance(),
+                     ResultSpecProto::default_instance());
+    ASSERT_THAT(results3.results(), SizeIs(1));
+    EXPECT_THAT(results3.results(0).document().uri(), Eq("person"));
+    EXPECT_THAT(results3.results(0).joined_results(), SizeIs(3));
+    EXPECT_THAT(results3.results(0).joined_results(0).document().uri(),
+                Eq("message/3"));
+    EXPECT_THAT(results3.results(0).joined_results(1).document().uri(),
+                Eq("message/2"));
+    EXPECT_THAT(results3.results(0).joined_results(2).document().uri(),
+                Eq("message/1"));
+  }
+}
+
+TEST_F(IcingSearchEngineInitializationTest,
+       RestoreIndexLoseQualifiedIdJoinIndex) {
+  // Test the following scenario: losing the entire qualified id join index
+  // directory. IcingSearchEngine should be able to recover qualified id join
+  // index. Several additional behaviors are also tested:
+  // - Index directory handling:
+  //   - Term index directory should be unaffected.
+  //   - Integer index directory should be unaffected.
+  //   - Qualified id join index directory should not be discarded since we've
+  //     already lost it. Start it from scratch.
+  // - Truncate indices:
+  //   - "TruncateTo()" for term index shouldn't take effect.
+  //   - "Clear()" shouldn't be called for integer index, i.e. no integer index
+  //     storage sub directories (path_expr = "*/integer_index_dir/*") should be
+  //     discarded.
+  //   - "Clear()" shouldn't be called for qualified id join index, i.e. no
+  //     underlying storage sub directory (path_expr =
+  //     "*/qualified_id_join_index_dir/*") should be discarded, since we start
+  //     it from scratch.
+
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("Person").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("name")
+                  .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("Message")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("body")
+                                        .SetDataTypeString(TERM_MATCH_PREFIX,
+                                                           TOKENIZER_PLAIN)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("indexableInteger")
+                                        .SetDataTypeInt64(NUMERIC_MATCH_RANGE)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("senderQualifiedId")
+                                        .SetDataTypeJoinableString(
+                                            JOINABLE_VALUE_TYPE_QUALIFIED_ID)
+                                        .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
+  DocumentProto person =
+      DocumentBuilder()
+          .SetKey("namespace", "person")
+          .SetSchema("Person")
+          .AddStringProperty("name", "person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto message =
+      DocumentBuilder()
+          .SetKey("namespace", "message/1")
+          .SetSchema("Message")
+          .AddStringProperty("body", kIpsumText)
+          .AddInt64Property("indexableInteger", 123)
+          .AddStringProperty("senderQualifiedId", "namespace#person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+
+  // 1. Create an index with 3 message documents.
+  {
+    TestIcingSearchEngine icing(
+        GetDefaultIcingOptions(), std::make_unique<Filesystem>(),
+        std::make_unique<IcingFilesystem>(), std::make_unique<FakeClock>(),
+        GetTestJniCache());
+
+    ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
+    ASSERT_THAT(icing.SetSchema(schema).status(), ProtoIsOk());
+
+    EXPECT_THAT(icing.Put(person).status(), ProtoIsOk());
+    EXPECT_THAT(icing.Put(message).status(), ProtoIsOk());
+    message = DocumentBuilder(message).SetUri("message/2").Build();
+    EXPECT_THAT(icing.Put(message).status(), ProtoIsOk());
+    message = DocumentBuilder(message).SetUri("message/3").Build();
+    EXPECT_THAT(icing.Put(message).status(), ProtoIsOk());
+  }
+
+  // 2. Delete the qualified id join index file to trigger RestoreIndexIfNeeded.
+  std::string qualified_id_join_index_dir = GetQualifiedIdJoinIndexDir();
+  filesystem()->DeleteDirectoryRecursively(qualified_id_join_index_dir.c_str());
+
+  // 3. Create the index again. This should trigger index restoration.
+  {
+    // Mock filesystem to observe and check the behavior of all indices.
+    auto mock_filesystem = std::make_unique<MockFilesystem>();
+    EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(_))
+        .WillRepeatedly(DoDefault());
+    // Ensure term index directory should never be discarded.
+    EXPECT_CALL(*mock_filesystem,
+                DeleteDirectoryRecursively(EndsWith("/index_dir")))
+        .Times(0);
+    // Ensure integer index directory should never be discarded since we've
+    // already lost it, and Clear() should never be called (i.e. storage sub
+    // directory "*/integer_index_dir/*" should never be discarded).
+    EXPECT_CALL(*mock_filesystem,
+                DeleteDirectoryRecursively(EndsWith("/integer_index_dir")))
+        .Times(0);
+    EXPECT_CALL(*mock_filesystem,
+                DeleteDirectoryRecursively(HasSubstr("/integer_index_dir/")))
+        .Times(0);
+    // Ensure qualified id join index directory should never be discarded, and
+    // Clear() should never be called (i.e. storage sub directory
+    // "*/qualified_id_join_index_dir/*" should never be discarded)
+    // since we start it from scratch.
+    EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(
+                                      EndsWith("/qualified_id_join_index_dir")))
+        .Times(0);
+    EXPECT_CALL(
+        *mock_filesystem,
+        DeleteDirectoryRecursively(HasSubstr("/qualified_id_join_index_dir/")))
+        .Times(0);
+
+    TestIcingSearchEngine icing(
+        GetDefaultIcingOptions(), std::move(mock_filesystem),
+        std::make_unique<IcingFilesystem>(), std::make_unique<FakeClock>(),
+        GetTestJniCache());
+    InitializeResultProto initialize_result = icing.Initialize();
+    ASSERT_THAT(initialize_result.status(), ProtoIsOk());
+    EXPECT_THAT(initialize_result.initialize_stats().index_restoration_cause(),
+                Eq(InitializeStatsProto::NONE));
+    EXPECT_THAT(
+        initialize_result.initialize_stats().integer_index_restoration_cause(),
+        Eq(InitializeStatsProto::NONE));
+    EXPECT_THAT(initialize_result.initialize_stats()
+                    .qualified_id_join_index_restoration_cause(),
+                Eq(InitializeStatsProto::INCONSISTENT_WITH_GROUND_TRUTH));
+
+    // Verify term index works normally
+    SearchSpecProto search_spec1;
+    search_spec1.set_query("body:consectetur");
+    search_spec1.set_term_match_type(TermMatchType::EXACT_ONLY);
+    SearchResultProto results1 =
+        icing.Search(search_spec1, ScoringSpecProto::default_instance(),
+                     ResultSpecProto::default_instance());
+    EXPECT_THAT(results1.status(), ProtoIsOk());
+    EXPECT_THAT(results1.next_page_token(), Eq(0));
+    // All documents should be retrievable.
+    ASSERT_THAT(results1.results(), SizeIs(3));
+    EXPECT_THAT(results1.results(0).document().uri(), Eq("message/3"));
+    EXPECT_THAT(results1.results(1).document().uri(), Eq("message/2"));
+    EXPECT_THAT(results1.results(2).document().uri(), Eq("message/1"));
+
+    // Verify integer index works normally
+    SearchSpecProto search_spec2;
+    search_spec2.set_query("indexableInteger == 123");
+    search_spec2.set_search_type(
+        SearchSpecProto::SearchType::EXPERIMENTAL_ICING_ADVANCED_QUERY);
+    search_spec2.add_enabled_features(std::string(kNumericSearchFeature));
+
+    SearchResultProto results2 =
+        icing.Search(search_spec2, ScoringSpecProto::default_instance(),
+                     ResultSpecProto::default_instance());
+    ASSERT_THAT(results2.results(), SizeIs(3));
+    EXPECT_THAT(results2.results(0).document().uri(), Eq("message/3"));
+    EXPECT_THAT(results2.results(1).document().uri(), Eq("message/2"));
+    EXPECT_THAT(results2.results(2).document().uri(), Eq("message/1"));
+
+    // Verify qualified id join index works normally: join a query for
+    // `name:person` with a child query for `body:consectetur` based on the
+    // child's `senderQualifiedId` field.
+    SearchSpecProto search_spec3;
+    search_spec3.set_term_match_type(TermMatchType::EXACT_ONLY);
+    search_spec3.set_query("name:person");
+    JoinSpecProto* join_spec = search_spec3.mutable_join_spec();
+    join_spec->set_max_joined_child_count(100);
+    join_spec->set_parent_property_expression(
+        std::string(JoinProcessor::kQualifiedIdExpr));
+    join_spec->set_child_property_expression("senderQualifiedId");
+    join_spec->set_aggregation_scoring_strategy(
+        JoinSpecProto::AggregationScoringStrategy::COUNT);
+    JoinSpecProto::NestedSpecProto* nested_spec =
+        join_spec->mutable_nested_spec();
+    SearchSpecProto* nested_search_spec = nested_spec->mutable_search_spec();
+    nested_search_spec->set_term_match_type(TermMatchType::EXACT_ONLY);
+    nested_search_spec->set_query("body:consectetur");
+    *nested_spec->mutable_scoring_spec() = GetDefaultScoringSpec();
+    *nested_spec->mutable_result_spec() = ResultSpecProto::default_instance();
+
+    SearchResultProto results3 =
+        icing.Search(search_spec3, ScoringSpecProto::default_instance(),
+                     ResultSpecProto::default_instance());
+    ASSERT_THAT(results3.results(), SizeIs(1));
+    EXPECT_THAT(results3.results(0).document().uri(), Eq("person"));
+    EXPECT_THAT(results3.results(0).joined_results(), SizeIs(3));
+    EXPECT_THAT(results3.results(0).joined_results(0).document().uri(),
+                Eq("message/3"));
+    EXPECT_THAT(results3.results(0).joined_results(1).document().uri(),
+                Eq("message/2"));
+    EXPECT_THAT(results3.results(0).joined_results(2).document().uri(),
+                Eq("message/1"));
   }
 }
 
@@ -1398,6 +2163,7 @@ TEST_F(IcingSearchEngineInitializationTest,
   // - Index directory handling:
   //   - Term index directory should be unaffected.
   //   - Integer index directory should be unaffected.
+  //   - Qualified id join index directory should be unaffected.
   // - Truncate indices:
   //   - "TruncateTo()" for term index should take effect and throw out the
   //     entire lite index. This should be sufficient to make term index
@@ -1405,39 +2171,82 @@ TEST_F(IcingSearchEngineInitializationTest,
   //   - "Clear()" shouldn't be called for integer index, i.e. no integer index
   //     storage sub directories (path_expr = "*/integer_index_dir/*") should be
   //     discarded.
-  DocumentProto document = DocumentBuilder()
-                               .SetKey("icing", "fake_type/0")
-                               .SetSchema("Message")
-                               .AddStringProperty("body", kIpsumText)
-                               .AddInt64Property("indexableInteger", 123)
-                               .Build();
-  // 1. Create an index with a LiteIndex that will only allow one document
-  // before needing a merge.
+  //   - "Clear()" shouldn't be called for qualified id join index, i.e. no
+  //     underlying storage sub directory (path_expr =
+  //     "*/qualified_id_join_index_dir/*") should be discarded.
+
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("Person").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("name")
+                  .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("Message")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("body")
+                                        .SetDataTypeString(TERM_MATCH_PREFIX,
+                                                           TOKENIZER_PLAIN)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("indexableInteger")
+                                        .SetDataTypeInt64(NUMERIC_MATCH_RANGE)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("senderQualifiedId")
+                                        .SetDataTypeJoinableString(
+                                            JOINABLE_VALUE_TYPE_QUALIFIED_ID)
+                                        .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
+  DocumentProto person =
+      DocumentBuilder()
+          .SetKey("namespace", "person")
+          .SetSchema("Person")
+          .AddStringProperty("name", "person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto message =
+      DocumentBuilder()
+          .SetKey("namespace", "message/1")
+          .SetSchema("Message")
+          .AddStringProperty("body", kIpsumText)
+          .AddInt64Property("indexableInteger", 123)
+          .AddStringProperty("senderQualifiedId", "namespace#person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+
+  // 1. Create an index with a LiteIndex that will only allow a person and a
+  //    message document before needing a merge.
   {
     IcingSearchEngineOptions options = GetDefaultIcingOptions();
-    options.set_index_merge_size(document.ByteSizeLong());
+    options.set_index_merge_size(person.ByteSizeLong() +
+                                 message.ByteSizeLong());
     TestIcingSearchEngine icing(options, std::make_unique<Filesystem>(),
                                 std::make_unique<IcingFilesystem>(),
                                 std::make_unique<FakeClock>(),
                                 GetTestJniCache());
 
     ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
-    ASSERT_THAT(icing.SetSchema(CreateMessageSchema()).status(), ProtoIsOk());
+    ASSERT_THAT(icing.SetSchema(schema).status(), ProtoIsOk());
 
-    // Add two documents. These should get merged into the main index.
-    EXPECT_THAT(icing.Put(document).status(), ProtoIsOk());
-    document = DocumentBuilder(document).SetUri("fake_type/1").Build();
-    EXPECT_THAT(icing.Put(document).status(), ProtoIsOk());
+    EXPECT_THAT(icing.Put(person).status(), ProtoIsOk());
+    // Add two message documents. These should get merged into the main index.
+    EXPECT_THAT(icing.Put(message).status(), ProtoIsOk());
+    message = DocumentBuilder(message).SetUri("message/2").Build();
+    EXPECT_THAT(icing.Put(message).status(), ProtoIsOk());
   }
 
   // 2. Manually add some data into term lite index and increment
   // last_added_document_id, but don't merge into the main index. This will
   // cause mismatched last_added_document_id with term index.
-  //   - Document store: [0, 1]
+  //   - Document store: [0, 1, 2]
   //   - Term index
-  //     - Main index: [0, 1]
-  //     - Lite index: [2]
-  //   - Integer index: [0, 1]
+  //     - Main index: [0, 1, 2]
+  //     - Lite index: [3]
+  //   - Integer index: [0, 1, 2]
+  //   - Qualified id join index: [0, 1, 2]
   {
     Filesystem filesystem;
     IcingFilesystem icing_filesystem;
@@ -1445,7 +2254,7 @@ TEST_F(IcingSearchEngineInitializationTest,
         std::unique_ptr<Index> index,
         Index::Create(
             Index::Options(GetIndexDir(),
-                           /*index_merge_size=*/document.ByteSizeLong()),
+                           /*index_merge_size=*/message.ByteSizeLong()),
             &filesystem, &icing_filesystem));
     DocumentId original_last_added_doc_id = index->last_added_document_id();
     index->set_last_added_document_id(original_last_added_doc_id + 1);
@@ -1458,8 +2267,7 @@ TEST_F(IcingSearchEngineInitializationTest,
 
   // 3. Create the index again.
   {
-    // Mock filesystem to observe and check the behavior of term index and
-    // integer index.
+    // Mock filesystem to observe and check the behavior of all indices.
     auto mock_filesystem = std::make_unique<MockFilesystem>();
     EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(_))
         .WillRepeatedly(DoDefault());
@@ -1477,9 +2285,19 @@ TEST_F(IcingSearchEngineInitializationTest,
     EXPECT_CALL(*mock_filesystem,
                 DeleteDirectoryRecursively(HasSubstr("/integer_index_dir/")))
         .Times(0);
+    // Ensure qualified id join index directory should never be discarded, and
+    // Clear() should never be called (i.e. storage sub directory
+    // "*/qualified_id_join_index_dir/*" should never be discarded).
+    EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(
+                                      EndsWith("/qualified_id_join_index_dir")))
+        .Times(0);
+    EXPECT_CALL(
+        *mock_filesystem,
+        DeleteDirectoryRecursively(HasSubstr("/qualified_id_join_index_dir/")))
+        .Times(0);
 
     IcingSearchEngineOptions options = GetDefaultIcingOptions();
-    options.set_index_merge_size(document.ByteSizeLong());
+    options.set_index_merge_size(message.ByteSizeLong());
     TestIcingSearchEngine icing(options, std::move(mock_filesystem),
                                 std::make_unique<IcingFilesystem>(),
                                 std::make_unique<FakeClock>(),
@@ -1493,10 +2311,13 @@ TEST_F(IcingSearchEngineInitializationTest,
     EXPECT_THAT(
         initialize_result.initialize_stats().integer_index_restoration_cause(),
         Eq(InitializeStatsProto::NONE));
+    EXPECT_THAT(initialize_result.initialize_stats()
+                    .qualified_id_join_index_restoration_cause(),
+                Eq(InitializeStatsProto::NONE));
 
     // Verify term index works normally
     SearchSpecProto search_spec1;
-    search_spec1.set_query("consectetur");
+    search_spec1.set_query("body:consectetur");
     search_spec1.set_term_match_type(TermMatchType::EXACT_ONLY);
     SearchResultProto results1 =
         icing.Search(search_spec1, ScoringSpecProto::default_instance(),
@@ -1505,8 +2326,8 @@ TEST_F(IcingSearchEngineInitializationTest,
     EXPECT_THAT(results1.next_page_token(), Eq(0));
     // Only the documents that were in the main index should be retrievable.
     ASSERT_THAT(results1.results(), SizeIs(2));
-    EXPECT_THAT(results1.results(0).document().uri(), Eq("fake_type/1"));
-    EXPECT_THAT(results1.results(1).document().uri(), Eq("fake_type/0"));
+    EXPECT_THAT(results1.results(0).document().uri(), Eq("message/2"));
+    EXPECT_THAT(results1.results(1).document().uri(), Eq("message/1"));
 
     // Verify integer index works normally
     SearchSpecProto search_spec2;
@@ -1519,11 +2340,43 @@ TEST_F(IcingSearchEngineInitializationTest,
         icing.Search(search_spec2, ScoringSpecProto::default_instance(),
                      ResultSpecProto::default_instance());
     ASSERT_THAT(results2.results(), SizeIs(2));
-    EXPECT_THAT(results2.results(0).document().uri(), Eq("fake_type/1"));
-    EXPECT_THAT(results2.results(1).document().uri(), Eq("fake_type/0"));
+    EXPECT_THAT(results2.results(0).document().uri(), Eq("message/2"));
+    EXPECT_THAT(results2.results(1).document().uri(), Eq("message/1"));
+
+    // Verify qualified id join index works normally: join a query for
+    // `name:person` with a child query for `body:consectetur` based on the
+    // child's `senderQualifiedId` field.
+    SearchSpecProto search_spec3;
+    search_spec3.set_term_match_type(TermMatchType::EXACT_ONLY);
+    search_spec3.set_query("name:person");
+    JoinSpecProto* join_spec = search_spec3.mutable_join_spec();
+    join_spec->set_max_joined_child_count(100);
+    join_spec->set_parent_property_expression(
+        std::string(JoinProcessor::kQualifiedIdExpr));
+    join_spec->set_child_property_expression("senderQualifiedId");
+    join_spec->set_aggregation_scoring_strategy(
+        JoinSpecProto::AggregationScoringStrategy::COUNT);
+    JoinSpecProto::NestedSpecProto* nested_spec =
+        join_spec->mutable_nested_spec();
+    SearchSpecProto* nested_search_spec = nested_spec->mutable_search_spec();
+    nested_search_spec->set_term_match_type(TermMatchType::EXACT_ONLY);
+    nested_search_spec->set_query("body:consectetur");
+    *nested_spec->mutable_scoring_spec() = GetDefaultScoringSpec();
+    *nested_spec->mutable_result_spec() = ResultSpecProto::default_instance();
+
+    SearchResultProto results3 =
+        icing.Search(search_spec3, ScoringSpecProto::default_instance(),
+                     ResultSpecProto::default_instance());
+    ASSERT_THAT(results3.results(), SizeIs(1));
+    EXPECT_THAT(results3.results(0).document().uri(), Eq("person"));
+    EXPECT_THAT(results3.results(0).joined_results(), SizeIs(2));
+    EXPECT_THAT(results3.results(0).joined_results(0).document().uri(),
+                Eq("message/2"));
+    EXPECT_THAT(results3.results(0).joined_results(1).document().uri(),
+                Eq("message/1"));
   }
 
-  // 4. Since document 2 doesn't exist, testing query = "foo" is not enough to
+  // 4. Since document 3 doesn't exist, testing query = "foo" is not enough to
   // verify the correctness of term index restoration. Instead, we have to check
   // hits for "foo" should not be found in term index.
   {
@@ -1533,7 +2386,7 @@ TEST_F(IcingSearchEngineInitializationTest,
         std::unique_ptr<Index> index,
         Index::Create(
             Index::Options(GetIndexDir(),
-                           /*index_merge_size=*/document.ByteSizeLong()),
+                           /*index_merge_size=*/message.ByteSizeLong()),
             &filesystem, &icing_filesystem));
     ICING_ASSERT_OK_AND_ASSIGN(
         std::unique_ptr<DocHitInfoIterator> doc_hit_info_iter,
@@ -1553,6 +2406,7 @@ TEST_F(IcingSearchEngineInitializationTest,
   // - Index directory handling:
   //   - Term index directory should be unaffected.
   //   - Integer index directory should be unaffected.
+  //   - Qualified id join index directory should be unaffected.
   // - Truncate indices:
   //   - "TruncateTo()" for term index should take effect and throw out the
   //     entire lite index. However, some valid data in term lite index were
@@ -1561,42 +2415,84 @@ TEST_F(IcingSearchEngineInitializationTest,
   //   - "Clear()" shouldn't be called for integer index, i.e. no integer index
   //     storage sub directories (path_expr = "*/integer_index_dir/*") should be
   //     discarded.
-  DocumentProto document = DocumentBuilder()
-                               .SetKey("icing", "fake_type/0")
-                               .SetSchema("Message")
-                               .AddStringProperty("body", kIpsumText)
-                               .AddInt64Property("indexableInteger", 123)
-                               .Build();
-  // 1. Create an index with a LiteIndex that will only allow one document
-  //    before needing a merge.
+  //   - "Clear()" shouldn't be called for qualified id join index, i.e. no
+  //     underlying storage sub directory (path_expr =
+  //     "*/qualified_id_join_index_dir/*") should be discarded.
+
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("Person").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("name")
+                  .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("Message")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("body")
+                                        .SetDataTypeString(TERM_MATCH_PREFIX,
+                                                           TOKENIZER_PLAIN)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("indexableInteger")
+                                        .SetDataTypeInt64(NUMERIC_MATCH_RANGE)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("senderQualifiedId")
+                                        .SetDataTypeJoinableString(
+                                            JOINABLE_VALUE_TYPE_QUALIFIED_ID)
+                                        .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
+  DocumentProto person =
+      DocumentBuilder()
+          .SetKey("namespace", "person")
+          .SetSchema("Person")
+          .AddStringProperty("name", "person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto message =
+      DocumentBuilder()
+          .SetKey("namespace", "message/1")
+          .SetSchema("Message")
+          .AddStringProperty("body", kIpsumText)
+          .AddInt64Property("indexableInteger", 123)
+          .AddStringProperty("senderQualifiedId", "namespace#person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+
+  // 1. Create an index with a LiteIndex that will only allow a person and a
+  //    message document before needing a merge.
   {
     IcingSearchEngineOptions options = GetDefaultIcingOptions();
-    options.set_index_merge_size(document.ByteSizeLong());
+    options.set_index_merge_size(message.ByteSizeLong());
     TestIcingSearchEngine icing(options, std::make_unique<Filesystem>(),
                                 std::make_unique<IcingFilesystem>(),
                                 std::make_unique<FakeClock>(),
                                 GetTestJniCache());
 
     ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
-    ASSERT_THAT(icing.SetSchema(CreateMessageSchema()).status(), ProtoIsOk());
+    ASSERT_THAT(icing.SetSchema(schema).status(), ProtoIsOk());
 
-    // Add two documents. These should get merged into the main index.
-    EXPECT_THAT(icing.Put(document).status(), ProtoIsOk());
-    document = DocumentBuilder(document).SetUri("fake_type/1").Build();
-    EXPECT_THAT(icing.Put(document).status(), ProtoIsOk());
+    EXPECT_THAT(icing.Put(person).status(), ProtoIsOk());
+    // Add two message documents. These should get merged into the main index.
+    EXPECT_THAT(icing.Put(message).status(), ProtoIsOk());
+    message = DocumentBuilder(message).SetUri("message/2").Build();
+    EXPECT_THAT(icing.Put(message).status(), ProtoIsOk());
     // Add one document. This one should get remain in the lite index.
-    document = DocumentBuilder(document).SetUri("fake_type/2").Build();
-    EXPECT_THAT(icing.Put(document).status(), ProtoIsOk());
+    message = DocumentBuilder(message).SetUri("message/3").Build();
+    EXPECT_THAT(icing.Put(message).status(), ProtoIsOk());
   }
 
   // 2. Manually add some data into term lite index and increment
   //    last_added_document_id, but don't merge into the main index. This will
   //    cause mismatched last_added_document_id with term index.
-  //   - Document store: [0, 1, 2]
+  //   - Document store: [0, 1, 2, 3]
   //   - Term index
-  //     - Main index: [0, 1]
-  //     - Lite index: [2, 3]
-  //   - Integer index: [0, 1, 2]
+  //     - Main index: [0, 1, 2]
+  //     - Lite index: [3, 4]
+  //   - Integer index: [0, 1, 2, 3]
+  //   - Qualified id join index: [0, 1, 2, 3]
   {
     Filesystem filesystem;
     IcingFilesystem icing_filesystem;
@@ -1604,7 +2500,7 @@ TEST_F(IcingSearchEngineInitializationTest,
         std::unique_ptr<Index> index,
         Index::Create(
             Index::Options(GetIndexDir(),
-                           /*index_merge_size=*/document.ByteSizeLong()),
+                           /*index_merge_size=*/message.ByteSizeLong()),
             &filesystem, &icing_filesystem));
     DocumentId original_last_added_doc_id = index->last_added_document_id();
     index->set_last_added_document_id(original_last_added_doc_id + 1);
@@ -1617,8 +2513,7 @@ TEST_F(IcingSearchEngineInitializationTest,
 
   // 3. Create the index again.
   {
-    // Mock filesystem to observe and check the behavior of term index and
-    // integer index.
+    // Mock filesystem to observe and check the behavior of all indices.
     auto mock_filesystem = std::make_unique<MockFilesystem>();
     EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(_))
         .WillRepeatedly(DoDefault());
@@ -1636,9 +2531,19 @@ TEST_F(IcingSearchEngineInitializationTest,
     EXPECT_CALL(*mock_filesystem,
                 DeleteDirectoryRecursively(HasSubstr("/integer_index_dir/")))
         .Times(0);
+    // Ensure qualified id join index directory should never be discarded, and
+    // Clear() should never be called (i.e. storage sub directory
+    // "*/qualified_id_join_index_dir/*" should never be discarded).
+    EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(
+                                      EndsWith("/qualified_id_join_index_dir")))
+        .Times(0);
+    EXPECT_CALL(
+        *mock_filesystem,
+        DeleteDirectoryRecursively(HasSubstr("/qualified_id_join_index_dir/")))
+        .Times(0);
 
     IcingSearchEngineOptions options = GetDefaultIcingOptions();
-    options.set_index_merge_size(document.ByteSizeLong());
+    options.set_index_merge_size(message.ByteSizeLong());
     TestIcingSearchEngine icing(options, std::move(mock_filesystem),
                                 std::make_unique<IcingFilesystem>(),
                                 std::make_unique<FakeClock>(),
@@ -1653,10 +2558,13 @@ TEST_F(IcingSearchEngineInitializationTest,
     EXPECT_THAT(
         initialize_result.initialize_stats().integer_index_restoration_cause(),
         Eq(InitializeStatsProto::NONE));
+    EXPECT_THAT(initialize_result.initialize_stats()
+                    .qualified_id_join_index_restoration_cause(),
+                Eq(InitializeStatsProto::NONE));
 
     // Verify term index works normally
     SearchSpecProto search_spec1;
-    search_spec1.set_query("consectetur");
+    search_spec1.set_query("body:consectetur");
     search_spec1.set_term_match_type(TermMatchType::EXACT_ONLY);
     SearchResultProto results1 =
         icing.Search(search_spec1, ScoringSpecProto::default_instance(),
@@ -1665,9 +2573,9 @@ TEST_F(IcingSearchEngineInitializationTest,
     EXPECT_THAT(results1.next_page_token(), Eq(0));
     // Only the documents that were in the main index should be retrievable.
     ASSERT_THAT(results1.results(), SizeIs(3));
-    EXPECT_THAT(results1.results(0).document().uri(), Eq("fake_type/2"));
-    EXPECT_THAT(results1.results(1).document().uri(), Eq("fake_type/1"));
-    EXPECT_THAT(results1.results(2).document().uri(), Eq("fake_type/0"));
+    EXPECT_THAT(results1.results(0).document().uri(), Eq("message/3"));
+    EXPECT_THAT(results1.results(1).document().uri(), Eq("message/2"));
+    EXPECT_THAT(results1.results(2).document().uri(), Eq("message/1"));
 
     // Verify integer index works normally
     SearchSpecProto search_spec2;
@@ -1680,12 +2588,46 @@ TEST_F(IcingSearchEngineInitializationTest,
         icing.Search(search_spec2, ScoringSpecProto::default_instance(),
                      ResultSpecProto::default_instance());
     ASSERT_THAT(results2.results(), SizeIs(3));
-    EXPECT_THAT(results2.results(0).document().uri(), Eq("fake_type/2"));
-    EXPECT_THAT(results2.results(1).document().uri(), Eq("fake_type/1"));
-    EXPECT_THAT(results2.results(2).document().uri(), Eq("fake_type/0"));
+    EXPECT_THAT(results2.results(0).document().uri(), Eq("message/3"));
+    EXPECT_THAT(results2.results(1).document().uri(), Eq("message/2"));
+    EXPECT_THAT(results2.results(2).document().uri(), Eq("message/1"));
+
+    // Verify qualified id join index works normally: join a query for
+    // `name:person` with a child query for `body:consectetur` based on the
+    // child's `senderQualifiedId` field.
+    SearchSpecProto search_spec3;
+    search_spec3.set_term_match_type(TermMatchType::EXACT_ONLY);
+    search_spec3.set_query("name:person");
+    JoinSpecProto* join_spec = search_spec3.mutable_join_spec();
+    join_spec->set_max_joined_child_count(100);
+    join_spec->set_parent_property_expression(
+        std::string(JoinProcessor::kQualifiedIdExpr));
+    join_spec->set_child_property_expression("senderQualifiedId");
+    join_spec->set_aggregation_scoring_strategy(
+        JoinSpecProto::AggregationScoringStrategy::COUNT);
+    JoinSpecProto::NestedSpecProto* nested_spec =
+        join_spec->mutable_nested_spec();
+    SearchSpecProto* nested_search_spec = nested_spec->mutable_search_spec();
+    nested_search_spec->set_term_match_type(TermMatchType::EXACT_ONLY);
+    nested_search_spec->set_query("body:consectetur");
+    *nested_spec->mutable_scoring_spec() = GetDefaultScoringSpec();
+    *nested_spec->mutable_result_spec() = ResultSpecProto::default_instance();
+
+    SearchResultProto results3 =
+        icing.Search(search_spec3, ScoringSpecProto::default_instance(),
+                     ResultSpecProto::default_instance());
+    ASSERT_THAT(results3.results(), SizeIs(1));
+    EXPECT_THAT(results3.results(0).document().uri(), Eq("person"));
+    EXPECT_THAT(results3.results(0).joined_results(), SizeIs(3));
+    EXPECT_THAT(results3.results(0).joined_results(0).document().uri(),
+                Eq("message/3"));
+    EXPECT_THAT(results3.results(0).joined_results(1).document().uri(),
+                Eq("message/2"));
+    EXPECT_THAT(results3.results(0).joined_results(2).document().uri(),
+                Eq("message/1"));
   }
 
-  // 4. Since document 3 doesn't exist, testing query = "foo" is not enough to
+  // 4. Since document 4 doesn't exist, testing query = "foo" is not enough to
   // verify the correctness of term index restoration. Instead, we have to check
   // hits for "foo" should not be found in term index.
   {
@@ -1695,7 +2637,7 @@ TEST_F(IcingSearchEngineInitializationTest,
         std::unique_ptr<Index> index,
         Index::Create(
             Index::Options(GetIndexDir(),
-                           /*index_merge_size=*/document.ByteSizeLong()),
+                           /*index_merge_size=*/message.ByteSizeLong()),
             &filesystem, &icing_filesystem));
     ICING_ASSERT_OK_AND_ASSIGN(
         std::unique_ptr<DocHitInfoIterator> doc_hit_info_iter,
@@ -1715,14 +2657,18 @@ TEST_F(IcingSearchEngineInitializationTest,
   // - Index directory handling:
   //   - Term index directory should be unaffected.
   //   - Integer index directory should be unaffected.
+  //   - Qualified id join index directory should be unaffected.
   // - Truncate indices:
   //   - "TruncateTo()" for term index should take effect and throw out the
   //     entire lite and main index. This should be sufficient to make term
   //     index consistent with document store (in this case, document store is
   //     empty as well), so reindexing should not take place.
-  //   - "Clear()" shouldn't be called for integer index, i.e. no integer index
-  //     storage sub directories (path_expr = "*/integer_index_dir/*") should be
+  //   - "Clear()" should be called for integer index. It is a special case when
+  //     document store has no document. Since there is no integer index storage
+  //     sub directories (path_expr = "*/integer_index_dir/*"), nothing will be
   //     discarded.
+  //   - "Clear()" should be called for qualified id join index. It is a special
+  //     case when document store has no document.
 
   // 1. Create an index with no document.
   {
@@ -1744,6 +2690,7 @@ TEST_F(IcingSearchEngineInitializationTest,
   //     - Main index: [0]
   //     - Lite index: [1]
   //   - Integer index: []
+  //   - Qualified id join index: []
   {
     Filesystem filesystem;
     IcingFilesystem icing_filesystem;
@@ -1774,8 +2721,7 @@ TEST_F(IcingSearchEngineInitializationTest,
 
   // 3. Create the index again. This should throw out the lite and main index.
   {
-    // Mock filesystem to observe and check the behavior of term index and
-    // integer index.
+    // Mock filesystem to observe and check the behavior of all indices.
     auto mock_filesystem = std::make_unique<MockFilesystem>();
     EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(_))
         .WillRepeatedly(DoDefault());
@@ -1784,15 +2730,25 @@ TEST_F(IcingSearchEngineInitializationTest,
     EXPECT_CALL(*mock_filesystem,
                 DeleteDirectoryRecursively(EndsWith("/index_dir")))
         .Times(0);
-    // Ensure integer index directory should never be discarded, and Clear()
-    // should never be called (i.e. storage sub directory
-    // "*/integer_index_dir/*" should never be discarded).
+    // Ensure integer index directory should never be discarded. Even though
+    // Clear() was called, it shouldn't take effect since there is no storage
+    // sub directory ("*/integer_index_dir/*") and nothing will be discarded.
     EXPECT_CALL(*mock_filesystem,
                 DeleteDirectoryRecursively(EndsWith("/integer_index_dir")))
         .Times(0);
     EXPECT_CALL(*mock_filesystem,
                 DeleteDirectoryRecursively(HasSubstr("/integer_index_dir/")))
         .Times(0);
+    // Ensure qualified id join index directory should never be discarded.
+    // Clear() was called and should discard and reinitialize the underlying
+    // mapper.
+    EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(
+                                      EndsWith("/qualified_id_join_index_dir")))
+        .Times(0);
+    EXPECT_CALL(
+        *mock_filesystem,
+        DeleteDirectoryRecursively(HasSubstr("/qualified_id_join_index_dir/")))
+        .Times(AtLeast(1));
 
     TestIcingSearchEngine icing(
         GetDefaultIcingOptions(), std::move(mock_filesystem),
@@ -1808,6 +2764,9 @@ TEST_F(IcingSearchEngineInitializationTest,
     EXPECT_THAT(
         initialize_result.initialize_stats().integer_index_restoration_cause(),
         Eq(InitializeStatsProto::NONE));
+    EXPECT_THAT(initialize_result.initialize_stats()
+                    .qualified_id_join_index_restoration_cause(),
+                Eq(InitializeStatsProto::NONE));
   }
 
   // 4. Since document 0, 1 don't exist, testing queries = "foo", "bar" are not
@@ -1846,6 +2805,7 @@ TEST_F(IcingSearchEngineInitializationTest,
   // - Index directory handling:
   //   - Term index directory should be unaffected.
   //   - Integer index directory should be unaffected.
+  //   - Qualified id join index directory should be unaffected.
   // - In RestoreIndexIfNecessary():
   //   - "TruncateTo()" for term index should take effect and throw out the
   //     entire lite and main index. However, some valid data in term main index
@@ -1854,13 +2814,53 @@ TEST_F(IcingSearchEngineInitializationTest,
   //   - "Clear()" shouldn't be called for integer index, i.e. no integer index
   //     storage sub directories (path_expr = "*/integer_index_dir/*") should be
   //     discarded.
-  DocumentProto document = DocumentBuilder()
-                               .SetKey("icing", "fake_type/0")
-                               .SetSchema("Message")
-                               .AddStringProperty("body", kIpsumText)
-                               .AddInt64Property("indexableInteger", 123)
-                               .Build();
-  // 1. Create an index with 3 documents.
+  //   - "Clear()" shouldn't be called for qualified id join index, i.e. no
+  //     underlying storage sub directory (path_expr =
+  //     "*/qualified_id_join_index_dir/*") should be discarded.
+
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("Person").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("name")
+                  .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("Message")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("body")
+                                        .SetDataTypeString(TERM_MATCH_PREFIX,
+                                                           TOKENIZER_PLAIN)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("indexableInteger")
+                                        .SetDataTypeInt64(NUMERIC_MATCH_RANGE)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("senderQualifiedId")
+                                        .SetDataTypeJoinableString(
+                                            JOINABLE_VALUE_TYPE_QUALIFIED_ID)
+                                        .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
+  DocumentProto person =
+      DocumentBuilder()
+          .SetKey("namespace", "person")
+          .SetSchema("Person")
+          .AddStringProperty("name", "person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto message =
+      DocumentBuilder()
+          .SetKey("namespace", "message/1")
+          .SetSchema("Message")
+          .AddStringProperty("body", kIpsumText)
+          .AddInt64Property("indexableInteger", 123)
+          .AddStringProperty("senderQualifiedId", "namespace#person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+
+  // 1. Create an index with 3 message documents.
   {
     TestIcingSearchEngine icing(
         GetDefaultIcingOptions(), std::make_unique<Filesystem>(),
@@ -1868,24 +2868,26 @@ TEST_F(IcingSearchEngineInitializationTest,
         GetTestJniCache());
 
     ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
-    ASSERT_THAT(icing.SetSchema(CreateMessageSchema()).status(), ProtoIsOk());
+    ASSERT_THAT(icing.SetSchema(schema).status(), ProtoIsOk());
 
-    EXPECT_THAT(icing.Put(document).status(), ProtoIsOk());
-    document = DocumentBuilder(document).SetUri("fake_type/1").Build();
-    EXPECT_THAT(icing.Put(document).status(), ProtoIsOk());
-    document = DocumentBuilder(document).SetUri("fake_type/2").Build();
-    EXPECT_THAT(icing.Put(document).status(), ProtoIsOk());
+    EXPECT_THAT(icing.Put(person).status(), ProtoIsOk());
+    EXPECT_THAT(icing.Put(message).status(), ProtoIsOk());
+    message = DocumentBuilder(message).SetUri("message/2").Build();
+    EXPECT_THAT(icing.Put(message).status(), ProtoIsOk());
+    message = DocumentBuilder(message).SetUri("message/3").Build();
+    EXPECT_THAT(icing.Put(message).status(), ProtoIsOk());
   }
 
   // 2. Manually add some data into term lite index and increment
   //    last_added_document_id. Merge some of them into the main index and keep
   //    others in the lite index. This will cause mismatched document id with
   //    document store.
-  //   - Document store: [0, 1, 2]
+  //   - Document store: [0, 1, 2, 3]
   //   - Term index
-  //     - Main index: [0, 1, 2, 3]
-  //     - Lite index: [4]
-  //   - Integer index: [0, 1, 2]
+  //     - Main index: [0, 1, 2, 3, 4]
+  //     - Lite index: [5]
+  //   - Integer index: [0, 1, 2, 3]
+  //   - Qualified id join index: [0, 1, 2, 3]
   {
     Filesystem filesystem;
     IcingFilesystem icing_filesystem;
@@ -1893,9 +2895,9 @@ TEST_F(IcingSearchEngineInitializationTest,
         std::unique_ptr<Index> index,
         Index::Create(
             Index::Options(GetIndexDir(),
-                           /*index_merge_size=*/document.ByteSizeLong()),
+                           /*index_merge_size=*/message.ByteSizeLong()),
             &filesystem, &icing_filesystem));
-    // Add hits for document 3 and merge.
+    // Add hits for document 4 and merge.
     DocumentId original_last_added_doc_id = index->last_added_document_id();
     index->set_last_added_document_id(original_last_added_doc_id + 1);
     Index::Editor editor =
@@ -1905,7 +2907,7 @@ TEST_F(IcingSearchEngineInitializationTest,
     ICING_ASSERT_OK(editor.IndexAllBufferedTerms());
     ICING_ASSERT_OK(index->Merge());
 
-    // Add hits for document 4 and don't merge.
+    // Add hits for document 5 and don't merge.
     index->set_last_added_document_id(original_last_added_doc_id + 2);
     editor = index->Edit(original_last_added_doc_id + 2, /*section_id=*/0,
                          TermMatchType::EXACT_ONLY, /*namespace_id=*/0);
@@ -1916,8 +2918,7 @@ TEST_F(IcingSearchEngineInitializationTest,
   // 3. Create the index again. This should throw out the lite and main index
   // and trigger index restoration.
   {
-    // Mock filesystem to observe and check the behavior of term index and
-    // integer index.
+    // Mock filesystem to observe and check the behavior of all indices.
     auto mock_filesystem = std::make_unique<MockFilesystem>();
     EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(_))
         .WillRepeatedly(DoDefault());
@@ -1935,6 +2936,16 @@ TEST_F(IcingSearchEngineInitializationTest,
     EXPECT_CALL(*mock_filesystem,
                 DeleteDirectoryRecursively(HasSubstr("/integer_index_dir/")))
         .Times(0);
+    // Ensure qualified id join index directory should never be discarded, and
+    // Clear() should never be called (i.e. storage sub directory
+    // "*/qualified_id_join_index_dir/*" should never be discarded).
+    EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(
+                                      EndsWith("/qualified_id_join_index_dir")))
+        .Times(0);
+    EXPECT_CALL(
+        *mock_filesystem,
+        DeleteDirectoryRecursively(HasSubstr("/qualified_id_join_index_dir/")))
+        .Times(0);
 
     TestIcingSearchEngine icing(
         GetDefaultIcingOptions(), std::move(mock_filesystem),
@@ -1950,10 +2961,13 @@ TEST_F(IcingSearchEngineInitializationTest,
     EXPECT_THAT(
         initialize_result.initialize_stats().integer_index_restoration_cause(),
         Eq(InitializeStatsProto::NONE));
+    EXPECT_THAT(initialize_result.initialize_stats()
+                    .qualified_id_join_index_restoration_cause(),
+                Eq(InitializeStatsProto::NONE));
 
     // Verify term index works normally
     SearchSpecProto search_spec1;
-    search_spec1.set_query("consectetur");
+    search_spec1.set_query("body:consectetur");
     search_spec1.set_term_match_type(TermMatchType::EXACT_ONLY);
     SearchResultProto results1 =
         icing.Search(search_spec1, ScoringSpecProto::default_instance(),
@@ -1962,9 +2976,9 @@ TEST_F(IcingSearchEngineInitializationTest,
     EXPECT_THAT(results1.next_page_token(), Eq(0));
     // Only the first document should be retrievable.
     ASSERT_THAT(results1.results(), SizeIs(3));
-    EXPECT_THAT(results1.results(0).document().uri(), Eq("fake_type/2"));
-    EXPECT_THAT(results1.results(1).document().uri(), Eq("fake_type/1"));
-    EXPECT_THAT(results1.results(2).document().uri(), Eq("fake_type/0"));
+    EXPECT_THAT(results1.results(0).document().uri(), Eq("message/3"));
+    EXPECT_THAT(results1.results(1).document().uri(), Eq("message/2"));
+    EXPECT_THAT(results1.results(2).document().uri(), Eq("message/1"));
 
     // Verify integer index works normally
     SearchSpecProto search_spec2;
@@ -1977,12 +2991,46 @@ TEST_F(IcingSearchEngineInitializationTest,
         icing.Search(search_spec2, ScoringSpecProto::default_instance(),
                      ResultSpecProto::default_instance());
     ASSERT_THAT(results2.results(), SizeIs(3));
-    EXPECT_THAT(results2.results(0).document().uri(), Eq("fake_type/2"));
-    EXPECT_THAT(results2.results(1).document().uri(), Eq("fake_type/1"));
-    EXPECT_THAT(results2.results(2).document().uri(), Eq("fake_type/0"));
+    EXPECT_THAT(results2.results(0).document().uri(), Eq("message/3"));
+    EXPECT_THAT(results2.results(1).document().uri(), Eq("message/2"));
+    EXPECT_THAT(results2.results(2).document().uri(), Eq("message/1"));
+
+    // Verify qualified id join index works normally: join a query for
+    // `name:person` with a child query for `body:consectetur` based on the
+    // child's `senderQualifiedId` field.
+    SearchSpecProto search_spec3;
+    search_spec3.set_term_match_type(TermMatchType::EXACT_ONLY);
+    search_spec3.set_query("name:person");
+    JoinSpecProto* join_spec = search_spec3.mutable_join_spec();
+    join_spec->set_max_joined_child_count(100);
+    join_spec->set_parent_property_expression(
+        std::string(JoinProcessor::kQualifiedIdExpr));
+    join_spec->set_child_property_expression("senderQualifiedId");
+    join_spec->set_aggregation_scoring_strategy(
+        JoinSpecProto::AggregationScoringStrategy::COUNT);
+    JoinSpecProto::NestedSpecProto* nested_spec =
+        join_spec->mutable_nested_spec();
+    SearchSpecProto* nested_search_spec = nested_spec->mutable_search_spec();
+    nested_search_spec->set_term_match_type(TermMatchType::EXACT_ONLY);
+    nested_search_spec->set_query("body:consectetur");
+    *nested_spec->mutable_scoring_spec() = GetDefaultScoringSpec();
+    *nested_spec->mutable_result_spec() = ResultSpecProto::default_instance();
+
+    SearchResultProto results3 =
+        icing.Search(search_spec3, ScoringSpecProto::default_instance(),
+                     ResultSpecProto::default_instance());
+    ASSERT_THAT(results3.results(), SizeIs(1));
+    EXPECT_THAT(results3.results(0).document().uri(), Eq("person"));
+    EXPECT_THAT(results3.results(0).joined_results(), SizeIs(3));
+    EXPECT_THAT(results3.results(0).joined_results(0).document().uri(),
+                Eq("message/3"));
+    EXPECT_THAT(results3.results(0).joined_results(1).document().uri(),
+                Eq("message/2"));
+    EXPECT_THAT(results3.results(0).joined_results(2).document().uri(),
+                Eq("message/1"));
   }
 
-  // 4. Since document 3, 4 don't exist, testing queries = "foo", "bar" are not
+  // 4. Since document 4, 5 don't exist, testing queries = "foo", "bar" are not
   // enough to verify the correctness of term index restoration. Instead, we
   // have to check hits for "foo", "bar" should not be found in term index.
   {
@@ -2018,6 +3066,7 @@ TEST_F(IcingSearchEngineInitializationTest,
   // - Index directory handling:
   //   - Term index directory should be unaffected.
   //   - Integer index directory should be unaffected.
+  //   - Qualified id join index directory should be unaffected.
   // - Truncate indices:
   //   - "TruncateTo()" for term index shouldn't take effect.
   //   - "Clear()" should be called for integer index and throw out all integer
@@ -2025,6 +3074,8 @@ TEST_F(IcingSearchEngineInitializationTest,
   //     "*/integer_index_dir/*") should be discarded. This should be sufficient
   //     to make integer index consistent with document store (in this case,
   //     document store is empty as well), so reindexing should not take place.
+  //   - "Clear()" should be called for qualified id join index. It is a special
+  //     case when document store has no document.
 
   // 1. Create an index with no document.
   {
@@ -2043,6 +3094,7 @@ TEST_F(IcingSearchEngineInitializationTest,
   //   - Document store: []
   //   - Term index: []
   //   - Integer index: [0]
+  //   - Qualified id join index: []
   {
     Filesystem filesystem;
     ICING_ASSERT_OK_AND_ASSIGN(
@@ -2060,8 +3112,7 @@ TEST_F(IcingSearchEngineInitializationTest,
 
   // 3. Create the index again. This should trigger index restoration.
   {
-    // Mock filesystem to observe and check the behavior of term index and
-    // integer index.
+    // Mock filesystem to observe and check the behavior of all indices.
     auto mock_filesystem = std::make_unique<MockFilesystem>();
     EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(_))
         .WillRepeatedly(DoDefault());
@@ -2078,6 +3129,16 @@ TEST_F(IcingSearchEngineInitializationTest,
     EXPECT_CALL(*mock_filesystem,
                 DeleteDirectoryRecursively(HasSubstr("/integer_index_dir/")))
         .Times(1);
+    // Ensure qualified id join index directory should never be discarded.
+    // Clear() was called and should discard and reinitialize the underlying
+    // mapper.
+    EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(
+                                      EndsWith("/qualified_id_join_index_dir")))
+        .Times(0);
+    EXPECT_CALL(
+        *mock_filesystem,
+        DeleteDirectoryRecursively(HasSubstr("/qualified_id_join_index_dir/")))
+        .Times(AtLeast(1));
 
     TestIcingSearchEngine icing(
         GetDefaultIcingOptions(), std::move(mock_filesystem),
@@ -2092,23 +3153,36 @@ TEST_F(IcingSearchEngineInitializationTest,
     EXPECT_THAT(
         initialize_result.initialize_stats().integer_index_restoration_cause(),
         Eq(InitializeStatsProto::NONE));
-  }
+    EXPECT_THAT(initialize_result.initialize_stats()
+                    .qualified_id_join_index_restoration_cause(),
+                Eq(InitializeStatsProto::NONE));
 
-  // 4. Since document 0 doesn't exist, testing numeric query
-  // "indexableInteger == 123" is not enough to verify the correctness of
-  // integer index restoration. Instead, we have to check hits for 123 should
-  // not be found in integer index.
-  {
-    Filesystem filesystem;
-    ICING_ASSERT_OK_AND_ASSIGN(
-        std::unique_ptr<IntegerIndex> integer_index,
-        IntegerIndex::Create(filesystem, GetIntegerIndexDir()));
-    ICING_ASSERT_OK_AND_ASSIGN(
-        std::unique_ptr<DocHitInfoIterator> doc_hit_info_iter,
-        integer_index->GetIterator(/*property_path=*/"indexableInteger",
-                                   /*key_lower=*/123, /*key_upper=*/123));
-    EXPECT_THAT(doc_hit_info_iter->Advance(),
-                StatusIs(libtextclassifier3::StatusCode::RESOURCE_EXHAUSTED));
+    // Verify that numeric query safely wiped out the pre-existing hit for
+    // 'indexableInteger' == 123. Add a new document without that value for
+    // 'indexableInteger' that will take docid=0. If the integer index was not
+    // rebuilt correctly, then it will still have the previously added hit for
+    // 'indexableInteger' == 123 for docid 0 and incorrectly return this new
+    // doc in a query.
+    DocumentProto another_message =
+        DocumentBuilder()
+            .SetKey("namespace", "message/1")
+            .SetSchema("Message")
+            .AddStringProperty("body", kIpsumText)
+            .AddInt64Property("indexableInteger", 456)
+            .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+            .Build();
+    EXPECT_THAT(icing.Put(another_message).status(), ProtoIsOk());
+    // Verify integer index works normally
+    SearchSpecProto search_spec;
+    search_spec.set_query("indexableInteger == 123");
+    search_spec.set_search_type(
+        SearchSpecProto::SearchType::EXPERIMENTAL_ICING_ADVANCED_QUERY);
+    search_spec.add_enabled_features(std::string(kNumericSearchFeature));
+
+    SearchResultProto results =
+        icing.Search(search_spec, ScoringSpecProto::default_instance(),
+                     ResultSpecProto::default_instance());
+    EXPECT_THAT(results.results(), IsEmpty());
   }
 }
 
@@ -2120,6 +3194,7 @@ TEST_F(IcingSearchEngineInitializationTest,
   // - Index directory handling:
   //   - Term index directory should be unaffected.
   //   - Integer index directory should be unaffected.
+  //   - Qualified id join index directory should be unaffected.
   // - Truncate indices:
   //   - "TruncateTo()" for term index shouldn't take effect.
   //   - "Clear()" should be called for integer index and throw out all integer
@@ -2127,13 +3202,53 @@ TEST_F(IcingSearchEngineInitializationTest,
   //     "*/integer_index_dir/*") should be discarded. However, some valid data
   //     in integer index were discarded together, so reindexing should still
   //     take place to recover them after clearing.
-  DocumentProto document = DocumentBuilder()
-                               .SetKey("icing", "fake_type/0")
-                               .SetSchema("Message")
-                               .AddStringProperty("body", kIpsumText)
-                               .AddInt64Property("indexableInteger", 123)
-                               .Build();
-  // 1. Create an index with 3 documents.
+  //   - "Clear()" shouldn't be called for qualified id join index, i.e. no
+  //     underlying storage sub directory (path_expr =
+  //     "*/qualified_id_join_index_dir/*") should be discarded.
+
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("Person").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("name")
+                  .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("Message")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("body")
+                                        .SetDataTypeString(TERM_MATCH_PREFIX,
+                                                           TOKENIZER_PLAIN)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("indexableInteger")
+                                        .SetDataTypeInt64(NUMERIC_MATCH_RANGE)
+                                        .SetCardinality(CARDINALITY_OPTIONAL))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("senderQualifiedId")
+                                        .SetDataTypeJoinableString(
+                                            JOINABLE_VALUE_TYPE_QUALIFIED_ID)
+                                        .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
+  DocumentProto person =
+      DocumentBuilder()
+          .SetKey("namespace", "person")
+          .SetSchema("Person")
+          .AddStringProperty("name", "person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto message =
+      DocumentBuilder()
+          .SetKey("namespace", "message/1")
+          .SetSchema("Message")
+          .AddStringProperty("body", kIpsumText)
+          .AddInt64Property("indexableInteger", 123)
+          .AddStringProperty("senderQualifiedId", "namespace#person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+
+  // 1. Create an index with message 3 documents.
   {
     TestIcingSearchEngine icing(
         GetDefaultIcingOptions(), std::make_unique<Filesystem>(),
@@ -2141,27 +3256,29 @@ TEST_F(IcingSearchEngineInitializationTest,
         GetTestJniCache());
 
     ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
-    ASSERT_THAT(icing.SetSchema(CreateMessageSchema()).status(), ProtoIsOk());
+    ASSERT_THAT(icing.SetSchema(schema).status(), ProtoIsOk());
 
-    EXPECT_THAT(icing.Put(document).status(), ProtoIsOk());
-    document = DocumentBuilder(document).SetUri("fake_type/1").Build();
-    EXPECT_THAT(icing.Put(document).status(), ProtoIsOk());
-    document = DocumentBuilder(document).SetUri("fake_type/2").Build();
-    EXPECT_THAT(icing.Put(document).status(), ProtoIsOk());
+    EXPECT_THAT(icing.Put(person).status(), ProtoIsOk());
+    EXPECT_THAT(icing.Put(message).status(), ProtoIsOk());
+    message = DocumentBuilder(message).SetUri("message/2").Build();
+    EXPECT_THAT(icing.Put(message).status(), ProtoIsOk());
+    message = DocumentBuilder(message).SetUri("message/3").Build();
+    EXPECT_THAT(icing.Put(message).status(), ProtoIsOk());
   }
 
   // 2. Manually add some data into integer index and increment
   //    last_added_document_id. This will cause mismatched document id with
   //    document store.
-  //   - Document store: [0, 1, 2]
-  //   - Term index: [0, 1, 2]
-  //   - Integer index: [0, 1, 2, 3]
+  //   - Document store: [0, 1, 2, 3]
+  //   - Term index: [0, 1, 2, 3]
+  //   - Integer index: [0, 1, 2, 3, 4]
+  //   - Qualified id join index: [0, 1, 2, 3]
   {
     Filesystem filesystem;
     ICING_ASSERT_OK_AND_ASSIGN(
         std::unique_ptr<IntegerIndex> integer_index,
         IntegerIndex::Create(filesystem, GetIntegerIndexDir()));
-    // Add hits for document 3.
+    // Add hits for document 4.
     DocumentId original_last_added_doc_id =
         integer_index->last_added_document_id();
     integer_index->set_last_added_document_id(original_last_added_doc_id + 1);
@@ -2174,8 +3291,7 @@ TEST_F(IcingSearchEngineInitializationTest,
 
   // 3. Create the index again. This should trigger index restoration.
   {
-    // Mock filesystem to observe and check the behavior of term index and
-    // integer index.
+    // Mock filesystem to observe and check the behavior of all indices.
     auto mock_filesystem = std::make_unique<MockFilesystem>();
     EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(_))
         .WillRepeatedly(DoDefault());
@@ -2192,6 +3308,16 @@ TEST_F(IcingSearchEngineInitializationTest,
     EXPECT_CALL(*mock_filesystem,
                 DeleteDirectoryRecursively(HasSubstr("/integer_index_dir/")))
         .Times(1);
+    // Ensure qualified id join index directory should never be discarded, and
+    // Clear() should never be called (i.e. storage sub directory
+    // "*/qualified_id_join_index_dir/*" should never be discarded).
+    EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(
+                                      EndsWith("/qualified_id_join_index_dir")))
+        .Times(0);
+    EXPECT_CALL(
+        *mock_filesystem,
+        DeleteDirectoryRecursively(HasSubstr("/qualified_id_join_index_dir/")))
+        .Times(0);
 
     TestIcingSearchEngine icing(
         GetDefaultIcingOptions(), std::move(mock_filesystem),
@@ -2204,10 +3330,13 @@ TEST_F(IcingSearchEngineInitializationTest,
     EXPECT_THAT(
         initialize_result.initialize_stats().integer_index_restoration_cause(),
         Eq(InitializeStatsProto::INCONSISTENT_WITH_GROUND_TRUTH));
+    EXPECT_THAT(initialize_result.initialize_stats()
+                    .qualified_id_join_index_restoration_cause(),
+                Eq(InitializeStatsProto::NONE));
 
     // Verify term index works normally
     SearchSpecProto search_spec1;
-    search_spec1.set_query("consectetur");
+    search_spec1.set_query("body:consectetur");
     search_spec1.set_term_match_type(TermMatchType::EXACT_ONLY);
     SearchResultProto results1 =
         icing.Search(search_spec1, ScoringSpecProto::default_instance(),
@@ -2216,9 +3345,9 @@ TEST_F(IcingSearchEngineInitializationTest,
     EXPECT_THAT(results1.next_page_token(), Eq(0));
     // All documents should be retrievable.
     ASSERT_THAT(results1.results(), SizeIs(3));
-    EXPECT_THAT(results1.results(0).document().uri(), Eq("fake_type/2"));
-    EXPECT_THAT(results1.results(1).document().uri(), Eq("fake_type/1"));
-    EXPECT_THAT(results1.results(2).document().uri(), Eq("fake_type/0"));
+    EXPECT_THAT(results1.results(0).document().uri(), Eq("message/3"));
+    EXPECT_THAT(results1.results(1).document().uri(), Eq("message/2"));
+    EXPECT_THAT(results1.results(2).document().uri(), Eq("message/1"));
 
     // Verify integer index works normally
     SearchSpecProto search_spec2;
@@ -2231,26 +3360,425 @@ TEST_F(IcingSearchEngineInitializationTest,
         icing.Search(search_spec2, ScoringSpecProto::default_instance(),
                      ResultSpecProto::default_instance());
     ASSERT_THAT(results2.results(), SizeIs(3));
-    EXPECT_THAT(results2.results(0).document().uri(), Eq("fake_type/2"));
-    EXPECT_THAT(results2.results(1).document().uri(), Eq("fake_type/1"));
-    EXPECT_THAT(results2.results(2).document().uri(), Eq("fake_type/0"));
+    EXPECT_THAT(results2.results(0).document().uri(), Eq("message/3"));
+    EXPECT_THAT(results2.results(1).document().uri(), Eq("message/2"));
+    EXPECT_THAT(results2.results(2).document().uri(), Eq("message/1"));
+
+    // Verify qualified id join index works normally: join a query for
+    // `name:person` with a child query for `body:consectetur` based on the
+    // child's `senderQualifiedId` field.
+    SearchSpecProto search_spec3;
+    search_spec3.set_term_match_type(TermMatchType::EXACT_ONLY);
+    search_spec3.set_query("name:person");
+    JoinSpecProto* join_spec = search_spec3.mutable_join_spec();
+    join_spec->set_max_joined_child_count(100);
+    join_spec->set_parent_property_expression(
+        std::string(JoinProcessor::kQualifiedIdExpr));
+    join_spec->set_child_property_expression("senderQualifiedId");
+    join_spec->set_aggregation_scoring_strategy(
+        JoinSpecProto::AggregationScoringStrategy::COUNT);
+    JoinSpecProto::NestedSpecProto* nested_spec =
+        join_spec->mutable_nested_spec();
+    SearchSpecProto* nested_search_spec = nested_spec->mutable_search_spec();
+    nested_search_spec->set_term_match_type(TermMatchType::EXACT_ONLY);
+    nested_search_spec->set_query("body:consectetur");
+    *nested_spec->mutable_scoring_spec() = GetDefaultScoringSpec();
+    *nested_spec->mutable_result_spec() = ResultSpecProto::default_instance();
+
+    SearchResultProto results3 =
+        icing.Search(search_spec3, ScoringSpecProto::default_instance(),
+                     ResultSpecProto::default_instance());
+    ASSERT_THAT(results3.results(), SizeIs(1));
+    EXPECT_THAT(results3.results(0).document().uri(), Eq("person"));
+    EXPECT_THAT(results3.results(0).joined_results(), SizeIs(3));
+    EXPECT_THAT(results3.results(0).joined_results(0).document().uri(),
+                Eq("message/3"));
+    EXPECT_THAT(results3.results(0).joined_results(1).document().uri(),
+                Eq("message/2"));
+    EXPECT_THAT(results3.results(0).joined_results(2).document().uri(),
+                Eq("message/1"));
+
+    // Verify that numeric index safely wiped out the pre-existing hit for
+    // 'indexableInteger' == 456. Add a new document without that value for
+    // 'indexableInteger' that will take docid=0. If the integer index was not
+    // rebuilt correctly, then it will still have the previously added hit for
+    // 'indexableInteger' == 456 for docid 0 and incorrectly return this new
+    // doc in a query.
+    DocumentProto another_message =
+        DocumentBuilder()
+            .SetKey("namespace", "message/4")
+            .SetSchema("Message")
+            .AddStringProperty("body", kIpsumText)
+            .AddStringProperty("senderQualifiedId", "namespace#person")
+            .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+            .Build();
+    EXPECT_THAT(icing.Put(another_message).status(), ProtoIsOk());
+    // Verify integer index works normally
+    SearchSpecProto search_spec;
+    search_spec.set_query("indexableInteger == 456");
+    search_spec.set_search_type(
+        SearchSpecProto::SearchType::EXPERIMENTAL_ICING_ADVANCED_QUERY);
+    search_spec.add_enabled_features(std::string(kNumericSearchFeature));
+
+    SearchResultProto results =
+        icing.Search(search_spec, ScoringSpecProto::default_instance(),
+                     ResultSpecProto::default_instance());
+    EXPECT_THAT(results.results(), IsEmpty());
+  }
+}
+
+TEST_F(IcingSearchEngineInitializationTest,
+       RestoreIndexTruncateQualifiedIdJoinIndexWithoutReindexing) {
+  // Test the following scenario: qualified id join index is *completely* ahead
+  // of document store. IcingSearchEngine should be able to recover qualified id
+  // join index. Several additional behaviors are also tested:
+  // - Index directory handling:
+  //   - Term index directory should be unaffected.
+  //   - Integer index directory should be unaffected.
+  //   - Qualified id join index directory should be unaffected.
+  // - Truncate indices:
+  //   - "TruncateTo()" for term index shouldn't take effect.
+  //   - "Clear()" should be called for integer index. It is a special case when
+  //     document store has no document. Since there is no integer index storage
+  //     sub directories (path_expr = "*/integer_index_dir/*"), nothing will be
+  //     discarded.
+  //   - "Clear()" should be called for qualified id join index and throw out
+  //     all data, i.e. discarding the underlying mapper (path_expr =
+  //     "*/qualified_id_join_index_dir/*") and reinitialize. This should be
+  //     sufficient to make qualified id join index consistent with document
+  //     store (in this case, document store is empty as well), so reindexing
+  //     should not take place.
+
+  // 1. Create an index with no document.
+  {
+    TestIcingSearchEngine icing(
+        GetDefaultIcingOptions(), std::make_unique<Filesystem>(),
+        std::make_unique<IcingFilesystem>(), std::make_unique<FakeClock>(),
+        GetTestJniCache());
+
+    ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
+    ASSERT_THAT(icing.SetSchema(CreateMessageSchema()).status(), ProtoIsOk());
   }
 
-  // 4. Since document 3 doesn't exist, testing numeric query
-  // "indexableInteger == 456" is not enough to verify the correctness of
-  // integer index restoration. Instead, we have to check hits for 456 should
-  // not be found in integer index.
+  // 2. Manually add some data into integer index and increment
+  //    last_added_document_id. This will cause mismatched document id with
+  //    document store.
+  //   - Document store: []
+  //   - Term index: []
+  //   - Integer index: []
+  //   - Qualified id join index: [0]
   {
     Filesystem filesystem;
     ICING_ASSERT_OK_AND_ASSIGN(
-        std::unique_ptr<IntegerIndex> integer_index,
-        IntegerIndex::Create(filesystem, GetIntegerIndexDir()));
+        std::unique_ptr<QualifiedIdTypeJoinableIndex> qualified_id_join_index,
+        QualifiedIdTypeJoinableIndex::Create(filesystem,
+                                             GetQualifiedIdJoinIndexDir()));
+    // Add data for document 0.
+    ASSERT_THAT(qualified_id_join_index->last_added_document_id(),
+                kInvalidDocumentId);
+    qualified_id_join_index->set_last_added_document_id(0);
+    ICING_ASSERT_OK(qualified_id_join_index->Put(
+        DocJoinInfo(/*document_id=*/0, /*joinable_property_id=*/0),
+        /*ref_qualified_id_str=*/"namespace#person"));
+  }
+
+  // 3. Create the index again. This should trigger index restoration.
+  {
+    // Mock filesystem to observe and check the behavior of all indices.
+    auto mock_filesystem = std::make_unique<MockFilesystem>();
+    EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(_))
+        .WillRepeatedly(DoDefault());
+    // Ensure term index directory should never be discarded.
+    EXPECT_CALL(*mock_filesystem,
+                DeleteDirectoryRecursively(EndsWith("/index_dir")))
+        .Times(0);
+    // Ensure integer index directory should never be discarded. Even though
+    // Clear() was called, it shouldn't take effect since there is no storage
+    // sub directory ("*/integer_index_dir/*") and nothing will be discarded.
+    EXPECT_CALL(*mock_filesystem,
+                DeleteDirectoryRecursively(EndsWith("/integer_index_dir")))
+        .Times(0);
+    EXPECT_CALL(*mock_filesystem,
+                DeleteDirectoryRecursively(HasSubstr("/integer_index_dir/")))
+        .Times(0);
+    // Ensure qualified id join index directory should never be discarded.
+    EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(
+                                      EndsWith("/qualified_id_join_index_dir")))
+        .Times(0);
+    // Clear() should be called to truncate qualified id join index and thus
+    // underlying storage sub directory (path_expr =
+    // "*/qualified_id_join_index_dir/*") should be discarded.
+    EXPECT_CALL(
+        *mock_filesystem,
+        DeleteDirectoryRecursively(HasSubstr("/qualified_id_join_index_dir/")))
+        .Times(AtLeast(1));
+
+    TestIcingSearchEngine icing(
+        GetDefaultIcingOptions(), std::move(mock_filesystem),
+        std::make_unique<IcingFilesystem>(), std::make_unique<FakeClock>(),
+        GetTestJniCache());
+    InitializeResultProto initialize_result = icing.Initialize();
+    ASSERT_THAT(initialize_result.status(), ProtoIsOk());
+    EXPECT_THAT(initialize_result.initialize_stats().index_restoration_cause(),
+                Eq(InitializeStatsProto::NONE));
+    EXPECT_THAT(
+        initialize_result.initialize_stats().integer_index_restoration_cause(),
+        Eq(InitializeStatsProto::NONE));
+    // Since truncating qualified id join index is sufficient to make it
+    // consistent with document store, replaying documents or reindexing
+    // shouldn't take place.
+    EXPECT_THAT(initialize_result.initialize_stats()
+                    .qualified_id_join_index_restoration_cause(),
+                Eq(InitializeStatsProto::NONE));
+  }
+
+  // 4. Since document 0 doesn't exist, testing join query is not enough to
+  // verify the correctness of qualified id join index restoration. Instead, we
+  // have to check the previously added data should not be found in qualified id
+  // join index.
+  {
+    Filesystem filesystem;
     ICING_ASSERT_OK_AND_ASSIGN(
-        std::unique_ptr<DocHitInfoIterator> doc_hit_info_iter,
-        integer_index->GetIterator(/*property_path=*/"indexableInteger",
-                                   /*key_lower=*/456, /*key_upper=*/456));
-    EXPECT_THAT(doc_hit_info_iter->Advance(),
-                StatusIs(libtextclassifier3::StatusCode::RESOURCE_EXHAUSTED));
+        std::unique_ptr<QualifiedIdTypeJoinableIndex> qualified_id_join_index,
+        QualifiedIdTypeJoinableIndex::Create(filesystem,
+                                             GetQualifiedIdJoinIndexDir()));
+    EXPECT_THAT(qualified_id_join_index->Get(
+                    DocJoinInfo(/*document_id=*/0, /*joinable_property_id=*/0)),
+                StatusIs(libtextclassifier3::StatusCode::NOT_FOUND));
+  }
+}
+
+TEST_F(IcingSearchEngineInitializationTest,
+       RestoreIndexTruncateQualifiedIdJoinIndexWithReindexing) {
+  // Test the following scenario: qualified id join index is *partially* ahead
+  // of document store. IcingSearchEngine should be able to recover qualified id
+  // join index. Several additional behaviors are also tested:
+  // - Index directory handling:
+  //   - Term index directory should be unaffected.
+  //   - Integer index directory should be unaffected.
+  //   - Qualified id join index directory should be unaffected.
+  // - Truncate indices:
+  //   - "TruncateTo()" for term index shouldn't take effect.
+  //   - "Clear()" shouldn't be called for integer index, i.e. no integer index
+  //     storage sub directories (path_expr = "*/integer_index_dir/*") should be
+  //     discarded.
+  //   - "Clear()" should be called for qualified id join index and throw out
+  //     all data, i.e. discarding the underlying mapper (path_expr =
+  //     "*/qualified_id_join_index_dir/*") and reinitialize. However, some
+  //     valid data in qualified id join index were discarded together, so
+  //     reindexing should still take place to recover them after clearing.
+
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("Person").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("name")
+                  .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("Message")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("body")
+                                        .SetDataTypeString(TERM_MATCH_PREFIX,
+                                                           TOKENIZER_PLAIN)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("indexableInteger")
+                                        .SetDataTypeInt64(NUMERIC_MATCH_RANGE)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("senderQualifiedId")
+                                        .SetDataTypeJoinableString(
+                                            JOINABLE_VALUE_TYPE_QUALIFIED_ID)
+                                        .SetCardinality(CARDINALITY_OPTIONAL)))
+          .Build();
+
+  DocumentProto person =
+      DocumentBuilder()
+          .SetKey("namespace", "person")
+          .SetSchema("Person")
+          .AddStringProperty("name", "person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto message =
+      DocumentBuilder()
+          .SetKey("namespace", "message/1")
+          .SetSchema("Message")
+          .AddStringProperty("body", kIpsumText)
+          .AddInt64Property("indexableInteger", 123)
+          .AddStringProperty("senderQualifiedId", "namespace#person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+
+  // 1. Create an index with message 3 documents.
+  {
+    TestIcingSearchEngine icing(
+        GetDefaultIcingOptions(), std::make_unique<Filesystem>(),
+        std::make_unique<IcingFilesystem>(), std::make_unique<FakeClock>(),
+        GetTestJniCache());
+
+    ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
+    ASSERT_THAT(icing.SetSchema(schema).status(), ProtoIsOk());
+
+    EXPECT_THAT(icing.Put(person).status(), ProtoIsOk());
+    EXPECT_THAT(icing.Put(message).status(), ProtoIsOk());
+    message = DocumentBuilder(message).SetUri("message/2").Build();
+    EXPECT_THAT(icing.Put(message).status(), ProtoIsOk());
+    message = DocumentBuilder(message).SetUri("message/3").Build();
+    EXPECT_THAT(icing.Put(message).status(), ProtoIsOk());
+  }
+
+  DocJoinInfo additional_data_key;
+  // 2. Manually add some data into qualified id join index and increment
+  //    last_added_document_id. This will cause mismatched document id with
+  //    document store.
+  //   - Document store: [0, 1, 2, 3]
+  //   - Term index: [0, 1, 2, 3]
+  //   - Integer index: [0, 1, 2, 3]
+  //   - Qualified id join index: [0, 1, 2, 3, 4]
+  {
+    Filesystem filesystem;
+    ICING_ASSERT_OK_AND_ASSIGN(
+        std::unique_ptr<QualifiedIdTypeJoinableIndex> qualified_id_join_index,
+        QualifiedIdTypeJoinableIndex::Create(filesystem,
+                                             GetQualifiedIdJoinIndexDir()));
+    // Add data for document 4.
+    DocumentId original_last_added_doc_id =
+        qualified_id_join_index->last_added_document_id();
+    qualified_id_join_index->set_last_added_document_id(
+        original_last_added_doc_id + 1);
+    additional_data_key =
+        DocJoinInfo(/*document_id=*/original_last_added_doc_id + 1,
+                    /*joinable_property_id=*/0);
+    ICING_ASSERT_OK(qualified_id_join_index->Put(
+        additional_data_key,
+        /*ref_qualified_id_str=*/"namespace#person"));
+  }
+
+  // 3. Create the index again. This should trigger index restoration.
+  {
+    // Mock filesystem to observe and check the behavior of all indices.
+    auto mock_filesystem = std::make_unique<MockFilesystem>();
+    EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(_))
+        .WillRepeatedly(DoDefault());
+    // Ensure term index directory should never be discarded.
+    EXPECT_CALL(*mock_filesystem,
+                DeleteDirectoryRecursively(EndsWith("/index_dir")))
+        .Times(0);
+    // Ensure integer index directory should never be discarded, and Clear()
+    // should never be called (i.e. storage sub directory
+    // "*/integer_index_dir/*" should never be discarded).
+    EXPECT_CALL(*mock_filesystem,
+                DeleteDirectoryRecursively(EndsWith("/integer_index_dir")))
+        .Times(0);
+    EXPECT_CALL(*mock_filesystem,
+                DeleteDirectoryRecursively(HasSubstr("/integer_index_dir/")))
+        .Times(0);
+    // Ensure qualified id join index directory should never be discarded.
+    EXPECT_CALL(*mock_filesystem, DeleteDirectoryRecursively(
+                                      EndsWith("/qualified_id_join_index_dir")))
+        .Times(0);
+    // Clear() should be called to truncate qualified id join index and thus
+    // underlying storage sub directory (path_expr =
+    // "*/qualified_id_join_index_dir/*") should be discarded.
+    EXPECT_CALL(
+        *mock_filesystem,
+        DeleteDirectoryRecursively(HasSubstr("/qualified_id_join_index_dir/")))
+        .Times(AtLeast(1));
+
+    TestIcingSearchEngine icing(
+        GetDefaultIcingOptions(), std::move(mock_filesystem),
+        std::make_unique<IcingFilesystem>(), std::make_unique<FakeClock>(),
+        GetTestJniCache());
+    InitializeResultProto initialize_result = icing.Initialize();
+    ASSERT_THAT(initialize_result.status(), ProtoIsOk());
+    EXPECT_THAT(initialize_result.initialize_stats().index_restoration_cause(),
+                Eq(InitializeStatsProto::NONE));
+    EXPECT_THAT(
+        initialize_result.initialize_stats().integer_index_restoration_cause(),
+        Eq(InitializeStatsProto::NONE));
+    EXPECT_THAT(initialize_result.initialize_stats()
+                    .qualified_id_join_index_restoration_cause(),
+                Eq(InitializeStatsProto::INCONSISTENT_WITH_GROUND_TRUTH));
+
+    // Verify term index works normally
+    SearchSpecProto search_spec1;
+    search_spec1.set_query("body:consectetur");
+    search_spec1.set_term_match_type(TermMatchType::EXACT_ONLY);
+    SearchResultProto results1 =
+        icing.Search(search_spec1, ScoringSpecProto::default_instance(),
+                     ResultSpecProto::default_instance());
+    EXPECT_THAT(results1.status(), ProtoIsOk());
+    EXPECT_THAT(results1.next_page_token(), Eq(0));
+    // All documents should be retrievable.
+    ASSERT_THAT(results1.results(), SizeIs(3));
+    EXPECT_THAT(results1.results(0).document().uri(), Eq("message/3"));
+    EXPECT_THAT(results1.results(1).document().uri(), Eq("message/2"));
+    EXPECT_THAT(results1.results(2).document().uri(), Eq("message/1"));
+
+    // Verify integer index works normally
+    SearchSpecProto search_spec2;
+    search_spec2.set_query("indexableInteger == 123");
+    search_spec2.set_search_type(
+        SearchSpecProto::SearchType::EXPERIMENTAL_ICING_ADVANCED_QUERY);
+    search_spec2.add_enabled_features(std::string(kNumericSearchFeature));
+
+    SearchResultProto results2 =
+        icing.Search(search_spec2, ScoringSpecProto::default_instance(),
+                     ResultSpecProto::default_instance());
+    ASSERT_THAT(results2.results(), SizeIs(3));
+    EXPECT_THAT(results2.results(0).document().uri(), Eq("message/3"));
+    EXPECT_THAT(results2.results(1).document().uri(), Eq("message/2"));
+    EXPECT_THAT(results2.results(2).document().uri(), Eq("message/1"));
+
+    // Verify qualified id join index works normally: join a query for
+    // `name:person` with a child query for `body:consectetur` based on the
+    // child's `senderQualifiedId` field.
+
+    // Add document 4 without "senderQualifiedId". If joinable index is not
+    // rebuilt correctly, then it will still have the previously added
+    // senderQualifiedId for document 4 and include document 4 incorrectly in
+    // the right side.
+    DocumentProto another_message =
+        DocumentBuilder()
+            .SetKey("namespace", "message/4")
+            .SetSchema("Message")
+            .AddStringProperty("body", kIpsumText)
+            .AddInt64Property("indexableInteger", 123)
+            .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+            .Build();
+    EXPECT_THAT(icing.Put(another_message).status(), ProtoIsOk());
+
+    SearchSpecProto search_spec3;
+    search_spec3.set_term_match_type(TermMatchType::EXACT_ONLY);
+    search_spec3.set_query("name:person");
+    JoinSpecProto* join_spec = search_spec3.mutable_join_spec();
+    join_spec->set_max_joined_child_count(100);
+    join_spec->set_parent_property_expression(
+        std::string(JoinProcessor::kQualifiedIdExpr));
+    join_spec->set_child_property_expression("senderQualifiedId");
+    join_spec->set_aggregation_scoring_strategy(
+        JoinSpecProto::AggregationScoringStrategy::COUNT);
+    JoinSpecProto::NestedSpecProto* nested_spec =
+        join_spec->mutable_nested_spec();
+    SearchSpecProto* nested_search_spec = nested_spec->mutable_search_spec();
+    nested_search_spec->set_term_match_type(TermMatchType::EXACT_ONLY);
+    nested_search_spec->set_query("body:consectetur");
+    *nested_spec->mutable_scoring_spec() = GetDefaultScoringSpec();
+    *nested_spec->mutable_result_spec() = ResultSpecProto::default_instance();
+
+    SearchResultProto results3 =
+        icing.Search(search_spec3, ScoringSpecProto::default_instance(),
+                     ResultSpecProto::default_instance());
+    ASSERT_THAT(results3.results(), SizeIs(1));
+    EXPECT_THAT(results3.results(0).document().uri(), Eq("person"));
+    EXPECT_THAT(results3.results(0).joined_results(), SizeIs(3));
+    EXPECT_THAT(results3.results(0).joined_results(0).document().uri(),
+                Eq("message/3"));
+    EXPECT_THAT(results3.results(0).joined_results(1).document().uri(),
+                Eq("message/2"));
+    EXPECT_THAT(results3.results(0).joined_results(2).document().uri(),
+                Eq("message/1"));
   }
 }
 
@@ -2308,6 +3836,9 @@ TEST_F(IcingSearchEngineInitializationTest,
     EXPECT_THAT(
         init_result.initialize_stats().integer_index_restoration_cause(),
         Eq(InitializeStatsProto::NONE));
+    EXPECT_THAT(init_result.initialize_stats()
+                    .qualified_id_join_index_restoration_cause(),
+                Eq(InitializeStatsProto::NONE));
   }
 }
 
@@ -2332,14 +3863,21 @@ TEST_F(IcingSearchEngineInitializationTest,
                     .AddProperty(PropertyConfigBuilder()
                                      .SetName("indexableInteger")
                                      .SetDataTypeInt64(NUMERIC_MATCH_RANGE)
+                                     .SetCardinality(CARDINALITY_OPTIONAL))
+                    .AddProperty(PropertyConfigBuilder()
+                                     .SetName("senderQualifiedId")
+                                     .SetDataTypeJoinableString(
+                                         JOINABLE_VALUE_TYPE_QUALIFIED_ID)
                                      .SetCardinality(CARDINALITY_OPTIONAL)))
             .Build();
-    // Set a schema for a single type that has no indexed contents.
+    // Set a schema for a single type that has no term, integer, join indexed
+    // contents.
     ASSERT_THAT(icing.SetSchema(schema).status(), ProtoIsOk());
 
     // Add a document that contains:
     // - No valid indexed string content - just punctuation
     // - No integer content - since it is an optional property
+    // - No qualified id content - since it is an optional property
     DocumentProto document = DocumentBuilder()
                                  .SetKey("icing", "fake_type/0")
                                  .SetSchema("Message")
@@ -2364,6 +3902,9 @@ TEST_F(IcingSearchEngineInitializationTest,
     EXPECT_THAT(
         init_result.initialize_stats().integer_index_restoration_cause(),
         Eq(InitializeStatsProto::NONE));
+    EXPECT_THAT(init_result.initialize_stats()
+                    .qualified_id_join_index_restoration_cause(),
+                Eq(InitializeStatsProto::NONE));
   }
 }
 
@@ -2454,6 +3995,9 @@ TEST_F(IcingSearchEngineInitializationTest,
   EXPECT_THAT(initialize_result_proto.initialize_stats()
                   .integer_index_restoration_cause(),
               Eq(InitializeStatsProto::NONE));
+  EXPECT_THAT(initialize_result_proto.initialize_stats()
+                  .qualified_id_join_index_restoration_cause(),
+              Eq(InitializeStatsProto::NONE));
   EXPECT_THAT(
       initialize_result_proto.initialize_stats().index_restoration_latency_ms(),
       Eq(0));
@@ -2525,6 +4069,9 @@ TEST_F(IcingSearchEngineInitializationTest,
                     .integer_index_restoration_cause(),
                 Eq(InitializeStatsProto::NONE));
     EXPECT_THAT(initialize_result_proto.initialize_stats()
+                    .qualified_id_join_index_restoration_cause(),
+                Eq(InitializeStatsProto::NONE));
+    EXPECT_THAT(initialize_result_proto.initialize_stats()
                     .index_restoration_latency_ms(),
                 Eq(0));
     EXPECT_THAT(initialize_result_proto.initialize_stats()
@@ -2616,6 +4163,9 @@ TEST_F(IcingSearchEngineInitializationTest,
                     .integer_index_restoration_cause(),
                 Eq(InitializeStatsProto::NONE));
     EXPECT_THAT(initialize_result_proto.initialize_stats()
+                    .qualified_id_join_index_restoration_cause(),
+                Eq(InitializeStatsProto::NONE));
+    EXPECT_THAT(initialize_result_proto.initialize_stats()
                     .index_restoration_latency_ms(),
                 Eq(0));
     EXPECT_THAT(initialize_result_proto.initialize_stats()
@@ -2667,6 +4217,9 @@ TEST_F(IcingSearchEngineInitializationTest,
                     .integer_index_restoration_cause(),
                 Eq(InitializeStatsProto::NONE));
     EXPECT_THAT(initialize_result_proto.initialize_stats()
+                    .qualified_id_join_index_restoration_cause(),
+                Eq(InitializeStatsProto::NONE));
+    EXPECT_THAT(initialize_result_proto.initialize_stats()
                     .index_restoration_latency_ms(),
                 Eq(10));
     EXPECT_THAT(initialize_result_proto.initialize_stats()
@@ -2728,6 +4281,111 @@ TEST_F(
                     .integer_index_restoration_cause(),
                 Eq(InitializeStatsProto::INCONSISTENT_WITH_GROUND_TRUTH));
     EXPECT_THAT(initialize_result_proto.initialize_stats()
+                    .qualified_id_join_index_restoration_cause(),
+                Eq(InitializeStatsProto::NONE));
+    EXPECT_THAT(initialize_result_proto.initialize_stats()
+                    .index_restoration_latency_ms(),
+                Eq(10));
+    EXPECT_THAT(initialize_result_proto.initialize_stats()
+                    .document_store_recovery_cause(),
+                Eq(InitializeStatsProto::NONE));
+    EXPECT_THAT(initialize_result_proto.initialize_stats()
+                    .document_store_recovery_latency_ms(),
+                Eq(0));
+    EXPECT_THAT(
+        initialize_result_proto.initialize_stats().document_store_data_status(),
+        Eq(InitializeStatsProto::NO_DATA_LOSS));
+    EXPECT_THAT(initialize_result_proto.initialize_stats()
+                    .schema_store_recovery_cause(),
+                Eq(InitializeStatsProto::NONE));
+    EXPECT_THAT(initialize_result_proto.initialize_stats()
+                    .schema_store_recovery_latency_ms(),
+                Eq(0));
+  }
+}
+
+TEST_F(
+    IcingSearchEngineInitializationTest,
+    InitializeShouldLogRecoveryCauseQualifiedIdJoinIndexInconsistentWithGroundTruth) {
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("Person").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("name")
+                  .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("Message")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("body")
+                                        .SetDataTypeString(TERM_MATCH_PREFIX,
+                                                           TOKENIZER_PLAIN)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("indexableInteger")
+                                        .SetDataTypeInt64(NUMERIC_MATCH_RANGE)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("senderQualifiedId")
+                                        .SetDataTypeJoinableString(
+                                            JOINABLE_VALUE_TYPE_QUALIFIED_ID)
+                                        .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
+  DocumentProto person =
+      DocumentBuilder()
+          .SetKey("namespace", "person")
+          .SetSchema("Person")
+          .AddStringProperty("name", "person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto message =
+      DocumentBuilder()
+          .SetKey("namespace", "message/1")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body")
+          .AddInt64Property("indexableInteger", 123)
+          .AddStringProperty("senderQualifiedId", "namespace#person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+
+  {
+    // Initialize and put documents.
+    IcingSearchEngine icing(GetDefaultIcingOptions(), GetTestJniCache());
+    ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
+    ASSERT_THAT(icing.SetSchema(schema).status(), ProtoIsOk());
+    EXPECT_THAT(icing.Put(person).status(), ProtoIsOk());
+    EXPECT_THAT(icing.Put(message).status(), ProtoIsOk());
+  }
+
+  {
+    // Delete the qualified id join index file to trigger RestoreIndexIfNeeded.
+    std::string qualified_id_join_index_dir = GetQualifiedIdJoinIndexDir();
+    filesystem()->DeleteDirectoryRecursively(
+        qualified_id_join_index_dir.c_str());
+  }
+
+  {
+    // Index is empty but ground truth is not. Index should be restored due to
+    // the inconsistency.
+    auto fake_clock = std::make_unique<FakeClock>();
+    fake_clock->SetTimerElapsedMilliseconds(10);
+    TestIcingSearchEngine icing(GetDefaultIcingOptions(),
+                                std::make_unique<Filesystem>(),
+                                std::make_unique<IcingFilesystem>(),
+                                std::move(fake_clock), GetTestJniCache());
+    InitializeResultProto initialize_result_proto = icing.Initialize();
+    EXPECT_THAT(initialize_result_proto.status(), ProtoIsOk());
+    EXPECT_THAT(
+        initialize_result_proto.initialize_stats().index_restoration_cause(),
+        Eq(InitializeStatsProto::NONE));
+    EXPECT_THAT(initialize_result_proto.initialize_stats()
+                    .integer_index_restoration_cause(),
+                Eq(InitializeStatsProto::NONE));
+    EXPECT_THAT(initialize_result_proto.initialize_stats()
+                    .qualified_id_join_index_restoration_cause(),
+                Eq(InitializeStatsProto::INCONSISTENT_WITH_GROUND_TRUTH));
+    EXPECT_THAT(initialize_result_proto.initialize_stats()
                     .index_restoration_latency_ms(),
                 Eq(10));
     EXPECT_THAT(initialize_result_proto.initialize_stats()
@@ -2808,6 +4466,9 @@ TEST_F(IcingSearchEngineInitializationTest,
                     .integer_index_restoration_cause(),
                 Eq(InitializeStatsProto::SCHEMA_CHANGES_OUT_OF_SYNC));
     EXPECT_THAT(initialize_result_proto.initialize_stats()
+                    .qualified_id_join_index_restoration_cause(),
+                Eq(InitializeStatsProto::SCHEMA_CHANGES_OUT_OF_SYNC));
+    EXPECT_THAT(initialize_result_proto.initialize_stats()
                     .index_restoration_latency_ms(),
                 Eq(10));
     EXPECT_THAT(initialize_result_proto.initialize_stats()
@@ -2844,6 +4505,9 @@ TEST_F(IcingSearchEngineInitializationTest,
                     .integer_index_restoration_cause(),
                 Eq(InitializeStatsProto::NONE));
     EXPECT_THAT(initialize_result_proto.initialize_stats()
+                    .qualified_id_join_index_restoration_cause(),
+                Eq(InitializeStatsProto::NONE));
+    EXPECT_THAT(initialize_result_proto.initialize_stats()
                     .index_restoration_latency_ms(),
                 Eq(0));
     EXPECT_THAT(initialize_result_proto.initialize_stats()
@@ -2906,6 +4570,9 @@ TEST_F(IcingSearchEngineInitializationTest,
   EXPECT_THAT(initialize_result_proto.initialize_stats()
                   .integer_index_restoration_cause(),
               Eq(InitializeStatsProto::NONE));
+  EXPECT_THAT(initialize_result_proto.initialize_stats()
+                  .qualified_id_join_index_restoration_cause(),
+              Eq(InitializeStatsProto::NONE));
   EXPECT_THAT(
       initialize_result_proto.initialize_stats().index_restoration_latency_ms(),
       Eq(10));
@@ -2966,6 +4633,113 @@ TEST_F(IcingSearchEngineInitializationTest,
   EXPECT_THAT(initialize_result_proto.initialize_stats()
                   .integer_index_restoration_cause(),
               Eq(InitializeStatsProto::IO_ERROR));
+  EXPECT_THAT(initialize_result_proto.initialize_stats()
+                  .qualified_id_join_index_restoration_cause(),
+              Eq(InitializeStatsProto::NONE));
+  EXPECT_THAT(
+      initialize_result_proto.initialize_stats().index_restoration_latency_ms(),
+      Eq(10));
+  EXPECT_THAT(initialize_result_proto.initialize_stats()
+                  .document_store_recovery_cause(),
+              Eq(InitializeStatsProto::NONE));
+  EXPECT_THAT(initialize_result_proto.initialize_stats()
+                  .document_store_recovery_latency_ms(),
+              Eq(0));
+  EXPECT_THAT(
+      initialize_result_proto.initialize_stats().document_store_data_status(),
+      Eq(InitializeStatsProto::NO_DATA_LOSS));
+  EXPECT_THAT(
+      initialize_result_proto.initialize_stats().schema_store_recovery_cause(),
+      Eq(InitializeStatsProto::NONE));
+  EXPECT_THAT(initialize_result_proto.initialize_stats()
+                  .schema_store_recovery_latency_ms(),
+              Eq(0));
+}
+
+TEST_F(IcingSearchEngineInitializationTest,
+       InitializeShouldLogRecoveryCauseQualifiedIdJoinIndexIOError) {
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("Person").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("name")
+                  .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("Message")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("body")
+                                        .SetDataTypeString(TERM_MATCH_PREFIX,
+                                                           TOKENIZER_PLAIN)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("indexableInteger")
+                                        .SetDataTypeInt64(NUMERIC_MATCH_RANGE)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("senderQualifiedId")
+                                        .SetDataTypeJoinableString(
+                                            JOINABLE_VALUE_TYPE_QUALIFIED_ID)
+                                        .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
+  DocumentProto person =
+      DocumentBuilder()
+          .SetKey("namespace", "person")
+          .SetSchema("Person")
+          .AddStringProperty("name", "person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto message =
+      DocumentBuilder()
+          .SetKey("namespace", "message/1")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body")
+          .AddInt64Property("indexableInteger", 123)
+          .AddStringProperty("senderQualifiedId", "namespace#person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+
+  {
+    // Initialize and put documents.
+    IcingSearchEngine icing(GetDefaultIcingOptions(), GetTestJniCache());
+    ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
+    ASSERT_THAT(icing.SetSchema(schema).status(), ProtoIsOk());
+    ASSERT_THAT(icing.Put(person).status(), ProtoIsOk());
+    ASSERT_THAT(icing.Put(message).status(), ProtoIsOk());
+  }
+
+  std::string qualified_id_join_index_metadata_file =
+      absl_ports::StrCat(GetQualifiedIdJoinIndexDir(), "/metadata");
+  auto mock_filesystem = std::make_unique<MockFilesystem>();
+  EXPECT_CALL(*mock_filesystem, PRead(A<const char*>(), _, _, _))
+      .WillRepeatedly(DoDefault());
+  // This fails QualifiedIdTypeJoinableIndex::Create() once.
+  EXPECT_CALL(
+      *mock_filesystem,
+      PRead(Matcher<const char*>(Eq(qualified_id_join_index_metadata_file)), _,
+            _, _))
+      .WillOnce(Return(false))
+      .WillRepeatedly(DoDefault());
+
+  auto fake_clock = std::make_unique<FakeClock>();
+  fake_clock->SetTimerElapsedMilliseconds(10);
+  TestIcingSearchEngine icing(GetDefaultIcingOptions(),
+                              std::move(mock_filesystem),
+                              std::make_unique<IcingFilesystem>(),
+                              std::move(fake_clock), GetTestJniCache());
+
+  InitializeResultProto initialize_result_proto = icing.Initialize();
+  EXPECT_THAT(initialize_result_proto.status(), ProtoIsOk());
+  EXPECT_THAT(
+      initialize_result_proto.initialize_stats().index_restoration_cause(),
+      Eq(InitializeStatsProto::NONE));
+  EXPECT_THAT(initialize_result_proto.initialize_stats()
+                  .integer_index_restoration_cause(),
+              Eq(InitializeStatsProto::NONE));
+  EXPECT_THAT(initialize_result_proto.initialize_stats()
+                  .qualified_id_join_index_restoration_cause(),
+              Eq(InitializeStatsProto::IO_ERROR));
   EXPECT_THAT(
       initialize_result_proto.initialize_stats().index_restoration_latency_ms(),
       Eq(10));
@@ -3038,6 +4812,9 @@ TEST_F(IcingSearchEngineInitializationTest,
   EXPECT_THAT(initialize_result_proto.initialize_stats()
                   .integer_index_restoration_cause(),
               Eq(InitializeStatsProto::NONE));
+  EXPECT_THAT(initialize_result_proto.initialize_stats()
+                  .qualified_id_join_index_restoration_cause(),
+              Eq(InitializeStatsProto::NONE));
   EXPECT_THAT(
       initialize_result_proto.initialize_stats().index_restoration_latency_ms(),
       Eq(0));
@@ -3095,6 +4872,9 @@ TEST_F(IcingSearchEngineInitializationTest,
                     .integer_index_restoration_cause(),
                 Eq(InitializeStatsProto::NONE));
     EXPECT_THAT(initialize_result_proto.initialize_stats()
+                    .qualified_id_join_index_restoration_cause(),
+                Eq(InitializeStatsProto::NONE));
+    EXPECT_THAT(initialize_result_proto.initialize_stats()
                     .index_restoration_latency_ms(),
                 Eq(0));
   }
diff --git a/icing/icing-search-engine_optimize_test.cc b/icing/icing-search-engine_optimize_test.cc
index b2c7a62..0c5cb7a 100644
--- a/icing/icing-search-engine_optimize_test.cc
+++ b/icing/icing-search-engine_optimize_test.cc
@@ -28,6 +28,7 @@
 #include "icing/file/mock-filesystem.h"
 #include "icing/icing-search-engine.h"
 #include "icing/jni/jni-cache.h"
+#include "icing/join/join-processor.h"
 #include "icing/portable/endian.h"
 #include "icing/portable/equals-proto.h"
 #include "icing/portable/platform.h"
@@ -123,46 +124,46 @@ IcingSearchEngineOptions GetDefaultIcingOptions() {
   return icing_options;
 }
 
-DocumentProto CreateMessageDocument(std::string name_space, std::string uri) {
-  return DocumentBuilder()
-      .SetKey(std::move(name_space), std::move(uri))
-      .SetSchema("Message")
-      .AddStringProperty("body", "message body")
-      .AddInt64Property("indexableInteger", 123)
-      .SetCreationTimestampMs(kDefaultCreationTimestampMs)
-      .Build();
-}
-
-SchemaProto CreateMessageSchema() {
-  return SchemaBuilder()
-      .AddType(SchemaTypeConfigBuilder()
-                   .SetType("Message")
-                   .AddProperty(PropertyConfigBuilder()
-                                    .SetName("body")
-                                    .SetDataTypeString(TERM_MATCH_PREFIX,
-                                                       TOKENIZER_PLAIN)
-                                    .SetCardinality(CARDINALITY_REQUIRED))
-                   .AddProperty(PropertyConfigBuilder()
-                                    .SetName("indexableInteger")
-                                    .SetDataTypeInt64(NUMERIC_MATCH_RANGE)
-                                    .SetCardinality(CARDINALITY_REQUIRED)))
-      .Build();
-}
-
 ScoringSpecProto GetDefaultScoringSpec() {
   ScoringSpecProto scoring_spec;
   scoring_spec.set_rank_by(ScoringSpecProto::RankingStrategy::DOCUMENT_SCORE);
   return scoring_spec;
 }
 
+// TODO(b/272145329): create SearchSpecBuilder, JoinSpecBuilder,
+// SearchResultProtoBuilder and ResultProtoBuilder for unit tests and build all
+// instances by them.
+
 TEST_F(IcingSearchEngineOptimizeTest,
        AllPageTokensShouldBeInvalidatedAfterOptimization) {
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("Message").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("body")
+                  .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
+  DocumentProto document1 =
+      DocumentBuilder()
+          .SetKey("namespace", "uri1")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body one")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto document2 =
+      DocumentBuilder()
+          .SetKey("namespace", "uri2")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body two")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+
   IcingSearchEngine icing(GetDefaultIcingOptions(), GetTestJniCache());
   ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
-  ASSERT_THAT(icing.SetSchema(CreateMessageSchema()).status(), ProtoIsOk());
+  ASSERT_THAT(icing.SetSchema(schema).status(), ProtoIsOk());
 
-  DocumentProto document1 = CreateMessageDocument("namespace", "uri1");
-  DocumentProto document2 = CreateMessageDocument("namespace", "uri2");
   ASSERT_THAT(icing.Put(document1).status(), ProtoIsOk());
   ASSERT_THAT(icing.Put(document2).status(), ProtoIsOk());
 
@@ -205,9 +206,24 @@ TEST_F(IcingSearchEngineOptimizeTest,
 }
 
 TEST_F(IcingSearchEngineOptimizeTest, OptimizationShouldRemoveDeletedDocs) {
-  IcingSearchEngineOptions icing_options = GetDefaultIcingOptions();
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("Message").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("body")
+                  .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
+  DocumentProto document1 =
+      DocumentBuilder()
+          .SetKey("namespace", "uri1")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body one")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
 
-  DocumentProto document1 = CreateMessageDocument("namespace", "uri1");
+  IcingSearchEngineOptions icing_options = GetDefaultIcingOptions();
 
   GetResultProto expected_get_result_proto;
   expected_get_result_proto.mutable_status()->set_code(StatusProto::NOT_FOUND);
@@ -216,7 +232,7 @@ TEST_F(IcingSearchEngineOptimizeTest, OptimizationShouldRemoveDeletedDocs) {
   {
     IcingSearchEngine icing(icing_options, GetTestJniCache());
     ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
-    ASSERT_THAT(icing.SetSchema(CreateMessageSchema()).status(), ProtoIsOk());
+    ASSERT_THAT(icing.SetSchema(schema).status(), ProtoIsOk());
     ASSERT_THAT(icing.Put(document1).status(), ProtoIsOk());
 
     // Deletes document1
@@ -247,10 +263,19 @@ TEST_F(IcingSearchEngineOptimizeTest, OptimizationShouldRemoveDeletedDocs) {
 
 TEST_F(IcingSearchEngineOptimizeTest,
        OptimizationShouldDeleteTemporaryDirectory) {
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("Message").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("body")
+                  .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
   IcingSearchEngineOptions icing_options = GetDefaultIcingOptions();
   IcingSearchEngine icing(icing_options, GetTestJniCache());
   ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
-  ASSERT_THAT(icing.SetSchema(CreateMessageSchema()).status(), ProtoIsOk());
+  ASSERT_THAT(icing.SetSchema(schema).status(), ProtoIsOk());
 
   // Create a tmp dir that will be used in Optimize() to swap files,
   // this validates that any tmp dirs will be deleted before using.
@@ -271,12 +296,26 @@ TEST_F(IcingSearchEngineOptimizeTest,
 }
 
 TEST_F(IcingSearchEngineOptimizeTest, GetOptimizeInfoHasCorrectStats) {
-  DocumentProto document1 = CreateMessageDocument("namespace", "uri1");
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("Message").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("body")
+                  .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
+  DocumentProto document1 =
+      DocumentBuilder()
+          .SetKey("namespace", "uri1")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body one")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
   DocumentProto document2 = DocumentBuilder()
                                 .SetKey("namespace", "uri2")
                                 .SetSchema("Message")
-                                .AddStringProperty("body", "message body")
-                                .AddInt64Property("indexableInteger", 456)
+                                .AddStringProperty("body", "message body two")
                                 .SetCreationTimestampMs(100)
                                 .SetTtlMs(500)
                                 .Build();
@@ -298,7 +337,7 @@ TEST_F(IcingSearchEngineOptimizeTest, GetOptimizeInfoHasCorrectStats) {
     EXPECT_THAT(optimize_info.estimated_optimizable_bytes(), Eq(0));
     EXPECT_THAT(optimize_info.time_since_last_optimize_ms(), Eq(0));
 
-    ASSERT_THAT(icing.SetSchema(CreateMessageSchema()).status(), ProtoIsOk());
+    ASSERT_THAT(icing.SetSchema(schema).status(), ProtoIsOk());
     ASSERT_THAT(icing.Put(document1).status(), ProtoIsOk());
 
     // Only have active documents, nothing is optimizable yet.
@@ -356,11 +395,50 @@ TEST_F(IcingSearchEngineOptimizeTest, GetOptimizeInfoHasCorrectStats) {
 }
 
 TEST_F(IcingSearchEngineOptimizeTest, GetAndPutShouldWorkAfterOptimization) {
-  DocumentProto document1 = CreateMessageDocument("namespace", "uri1");
-  DocumentProto document2 = CreateMessageDocument("namespace", "uri2");
-  DocumentProto document3 = CreateMessageDocument("namespace", "uri3");
-  DocumentProto document4 = CreateMessageDocument("namespace", "uri4");
-  DocumentProto document5 = CreateMessageDocument("namespace", "uri5");
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("Message").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("body")
+                  .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
+  DocumentProto document1 =
+      DocumentBuilder()
+          .SetKey("namespace", "uri1")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body one")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto document2 =
+      DocumentBuilder()
+          .SetKey("namespace", "uri2")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body two")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto document3 =
+      DocumentBuilder()
+          .SetKey("namespace", "uri3")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body three")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto document4 =
+      DocumentBuilder()
+          .SetKey("namespace", "uri4")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body four")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto document5 =
+      DocumentBuilder()
+          .SetKey("namespace", "uri5")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body five")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
 
   GetResultProto expected_get_result_proto;
   expected_get_result_proto.mutable_status()->set_code(StatusProto::OK);
@@ -368,7 +446,7 @@ TEST_F(IcingSearchEngineOptimizeTest, GetAndPutShouldWorkAfterOptimization) {
   {
     IcingSearchEngine icing(GetDefaultIcingOptions(), GetTestJniCache());
     ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
-    ASSERT_THAT(icing.SetSchema(CreateMessageSchema()).status(), ProtoIsOk());
+    ASSERT_THAT(icing.SetSchema(schema).status(), ProtoIsOk());
 
     ASSERT_THAT(icing.Put(document1).status(), ProtoIsOk());
     ASSERT_THAT(icing.Put(document2).status(), ProtoIsOk());
@@ -474,12 +552,34 @@ TEST_F(IcingSearchEngineOptimizeTest,
 }
 
 TEST_F(IcingSearchEngineOptimizeTest, DeleteShouldWorkAfterOptimization) {
-  DocumentProto document1 = CreateMessageDocument("namespace", "uri1");
-  DocumentProto document2 = CreateMessageDocument("namespace", "uri2");
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("Message").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("body")
+                  .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
+  DocumentProto document1 =
+      DocumentBuilder()
+          .SetKey("namespace", "uri1")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body one")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto document2 =
+      DocumentBuilder()
+          .SetKey("namespace", "uri2")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body two")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+
   {
     IcingSearchEngine icing(GetDefaultIcingOptions(), GetTestJniCache());
     ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
-    ASSERT_THAT(icing.SetSchema(CreateMessageSchema()).status(), ProtoIsOk());
+    ASSERT_THAT(icing.SetSchema(schema).status(), ProtoIsOk());
     ASSERT_THAT(icing.Put(document1).status(), ProtoIsOk());
     ASSERT_THAT(icing.Put(document2).status(), ProtoIsOk());
     ASSERT_THAT(icing.Optimize().status(), ProtoIsOk());
@@ -557,13 +657,14 @@ TEST_F(IcingSearchEngineOptimizeTest, OptimizationFailureUninitializesIcing) {
   ASSERT_THAT(icing.Optimize().status(), ProtoStatusIs(StatusProto::INTERNAL));
 
   // Ordinary operations should fail safely.
-  SchemaProto simple_schema;
-  auto type = simple_schema.add_types();
-  type->set_schema_type("type0");
-  auto property = type->add_properties();
-  property->set_property_name("prop0");
-  property->set_data_type(PropertyConfigProto::DataType::STRING);
-  property->set_cardinality(PropertyConfigProto::Cardinality::OPTIONAL);
+  SchemaProto simple_schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("type0").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("prop0")
+                  .SetDataType(TYPE_STRING)
+                  .SetCardinality(CARDINALITY_OPTIONAL)))
+          .Build();
 
   DocumentProto simple_doc = DocumentBuilder()
                                  .SetKey("namespace0", "uri0")
@@ -606,27 +707,30 @@ TEST_F(IcingSearchEngineOptimizeTest, OptimizationFailureUninitializesIcing) {
 
 TEST_F(IcingSearchEngineOptimizeTest, SetSchemaShouldWorkAfterOptimization) {
   // Creates 3 test schemas
-  SchemaProto schema1 = SchemaProto(CreateMessageSchema());
+  SchemaProto schema1 =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("Message").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("body")
+                  .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
 
   SchemaProto schema2 = SchemaProto(schema1);
-  auto new_property2 = schema2.mutable_types(0)->add_properties();
-  new_property2->set_property_name("property2");
-  new_property2->set_data_type(PropertyConfigProto::DataType::STRING);
-  new_property2->set_cardinality(PropertyConfigProto::Cardinality::OPTIONAL);
-  new_property2->mutable_string_indexing_config()->set_term_match_type(
-      TermMatchType::PREFIX);
-  new_property2->mutable_string_indexing_config()->set_tokenizer_type(
-      StringIndexingConfig::TokenizerType::PLAIN);
+  *schema2.mutable_types(0)->add_properties() =
+      PropertyConfigBuilder()
+          .SetName("property2")
+          .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+          .SetCardinality(CARDINALITY_OPTIONAL)
+          .Build();
 
   SchemaProto schema3 = SchemaProto(schema2);
-  auto new_property3 = schema3.mutable_types(0)->add_properties();
-  new_property3->set_property_name("property3");
-  new_property3->set_data_type(PropertyConfigProto::DataType::STRING);
-  new_property3->set_cardinality(PropertyConfigProto::Cardinality::OPTIONAL);
-  new_property3->mutable_string_indexing_config()->set_term_match_type(
-      TermMatchType::PREFIX);
-  new_property3->mutable_string_indexing_config()->set_tokenizer_type(
-      StringIndexingConfig::TokenizerType::PLAIN);
+  *schema3.mutable_types(0)->add_properties() =
+      PropertyConfigBuilder()
+          .SetName("property3")
+          .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+          .SetCardinality(CARDINALITY_OPTIONAL)
+          .Build();
 
   {
     IcingSearchEngine icing(GetDefaultIcingOptions(), GetTestJniCache());
@@ -644,7 +748,29 @@ TEST_F(IcingSearchEngineOptimizeTest, SetSchemaShouldWorkAfterOptimization) {
 }
 
 TEST_F(IcingSearchEngineOptimizeTest, SearchShouldWorkAfterOptimization) {
-  DocumentProto document = CreateMessageDocument("namespace", "uri");
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("Message")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("body")
+                                        .SetDataTypeString(TERM_MATCH_PREFIX,
+                                                           TOKENIZER_PLAIN)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("indexableInteger")
+                                        .SetDataTypeInt64(NUMERIC_MATCH_RANGE)
+                                        .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
+  DocumentProto document =
+      DocumentBuilder()
+          .SetKey("namespace", "uri")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body")
+          .AddInt64Property("indexableInteger", 123)
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
 
   SearchSpecProto search_spec1;
   search_spec1.set_term_match_type(TermMatchType::PREFIX);
@@ -664,7 +790,7 @@ TEST_F(IcingSearchEngineOptimizeTest, SearchShouldWorkAfterOptimization) {
   {
     IcingSearchEngine icing(GetDefaultIcingOptions(), GetTestJniCache());
     ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
-    ASSERT_THAT(icing.SetSchema(CreateMessageSchema()).status(), ProtoIsOk());
+    ASSERT_THAT(icing.SetSchema(schema).status(), ProtoIsOk());
     ASSERT_THAT(icing.Put(document).status(), ProtoIsOk());
     ASSERT_THAT(icing.Optimize().status(), ProtoIsOk());
 
@@ -703,14 +829,308 @@ TEST_F(IcingSearchEngineOptimizeTest, SearchShouldWorkAfterOptimization) {
 }
 
 TEST_F(IcingSearchEngineOptimizeTest,
+       JoinShouldWorkAfterOptimizationDeleteParent) {
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("Person").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("name")
+                  .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("Message")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("body")
+                                        .SetDataTypeString(TERM_MATCH_PREFIX,
+                                                           TOKENIZER_PLAIN)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("senderQualifiedId")
+                                        .SetDataTypeJoinableString(
+                                            JOINABLE_VALUE_TYPE_QUALIFIED_ID)
+                                        .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
+  DocumentProto person1 =
+      DocumentBuilder()
+          .SetKey("namespace", "person1")
+          .SetSchema("Person")
+          .AddStringProperty("name", "person one")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto person2 =
+      DocumentBuilder()
+          .SetKey("namespace", "person2")
+          .SetSchema("Person")
+          .AddStringProperty("name", "person two")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+
+  DocumentProto message1 =
+      DocumentBuilder()
+          .SetKey("namespace", "message1")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body one")
+          .AddStringProperty("senderQualifiedId", "namespace#person1")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto message2 =
+      DocumentBuilder()
+          .SetKey("namespace", "message2")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body two")
+          .AddStringProperty("senderQualifiedId", "namespace#person1")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto message3 =
+      DocumentBuilder()
+          .SetKey("namespace", "message3")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body three")
+          .AddStringProperty("senderQualifiedId", "namespace#person2")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+
+  // Prepare join search spec to join a query for `name:person` with a child
+  // query for `body:message` based on the child's `senderQualifiedId` field.
+  SearchSpecProto search_spec;
+  search_spec.set_term_match_type(TermMatchType::EXACT_ONLY);
+  search_spec.set_query("name:person");
+  JoinSpecProto* join_spec = search_spec.mutable_join_spec();
+  join_spec->set_max_joined_child_count(100);
+  join_spec->set_parent_property_expression(
+      std::string(JoinProcessor::kQualifiedIdExpr));
+  join_spec->set_child_property_expression("senderQualifiedId");
+  join_spec->set_aggregation_scoring_strategy(
+      JoinSpecProto::AggregationScoringStrategy::COUNT);
+  JoinSpecProto::NestedSpecProto* nested_spec =
+      join_spec->mutable_nested_spec();
+  SearchSpecProto* nested_search_spec = nested_spec->mutable_search_spec();
+  nested_search_spec->set_term_match_type(TermMatchType::EXACT_ONLY);
+  nested_search_spec->set_query("body:message");
+  *nested_spec->mutable_scoring_spec() = GetDefaultScoringSpec();
+  *nested_spec->mutable_result_spec() = ResultSpecProto::default_instance();
+
+  // Person1 is going to be deleted below. Only person2 which is joined with
+  // message3 should match the query.
+  SearchResultProto expected_search_result_proto;
+  expected_search_result_proto.mutable_status()->set_code(StatusProto::OK);
+  SearchResultProto::ResultProto* result_proto =
+      expected_search_result_proto.mutable_results()->Add();
+  *result_proto->mutable_document() = person2;
+  *result_proto->mutable_joined_results()->Add()->mutable_document() = message3;
+
+  {
+    IcingSearchEngine icing(GetDefaultIcingOptions(), GetTestJniCache());
+    ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
+    ASSERT_THAT(icing.SetSchema(schema).status(), ProtoIsOk());
+    ASSERT_THAT(icing.Put(person1).status(), ProtoIsOk());
+    ASSERT_THAT(icing.Put(person2).status(), ProtoIsOk());
+    ASSERT_THAT(icing.Put(message1).status(), ProtoIsOk());
+    ASSERT_THAT(icing.Put(message2).status(), ProtoIsOk());
+    ASSERT_THAT(icing.Put(message3).status(), ProtoIsOk());
+    // Delete parent document: person1
+    ASSERT_THAT(icing.Delete("namespace", "person1").status(), ProtoIsOk());
+    ASSERT_THAT(icing.Optimize().status(), ProtoIsOk());
+
+    // Validates that join search query works right after Optimize()
+    SearchResultProto search_result_proto =
+        icing.Search(search_spec, GetDefaultScoringSpec(),
+                     ResultSpecProto::default_instance());
+    EXPECT_THAT(search_result_proto, EqualsSearchResultIgnoreStatsAndScores(
+                                         expected_search_result_proto));
+  }  // Destroys IcingSearchEngine to make sure nothing is cached.
+
+  IcingSearchEngine icing(GetDefaultIcingOptions(), GetTestJniCache());
+  EXPECT_THAT(icing.Initialize().status(), ProtoIsOk());
+
+  SearchResultProto search_result_proto =
+      icing.Search(search_spec, GetDefaultScoringSpec(),
+                   ResultSpecProto::default_instance());
+  EXPECT_THAT(search_result_proto, EqualsSearchResultIgnoreStatsAndScores(
+                                       expected_search_result_proto));
+}
+
+TEST_F(IcingSearchEngineOptimizeTest,
+       JoinShouldWorkAfterOptimizationDeleteChild) {
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("Person").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("name")
+                  .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("Message")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("body")
+                                        .SetDataTypeString(TERM_MATCH_PREFIX,
+                                                           TOKENIZER_PLAIN)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("senderQualifiedId")
+                                        .SetDataTypeJoinableString(
+                                            JOINABLE_VALUE_TYPE_QUALIFIED_ID)
+                                        .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
+  DocumentProto person1 =
+      DocumentBuilder()
+          .SetKey("namespace", "person1")
+          .SetSchema("Person")
+          .AddStringProperty("name", "person one")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto person2 =
+      DocumentBuilder()
+          .SetKey("namespace", "person2")
+          .SetSchema("Person")
+          .AddStringProperty("name", "person two")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+
+  DocumentProto message1 =
+      DocumentBuilder()
+          .SetKey("namespace", "message1")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body one")
+          .AddStringProperty("senderQualifiedId", "namespace#person1")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto message2 =
+      DocumentBuilder()
+          .SetKey("namespace", "message2")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body two")
+          .AddStringProperty("senderQualifiedId", "namespace#person1")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto message3 =
+      DocumentBuilder()
+          .SetKey("namespace", "message3")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body three")
+          .AddStringProperty("senderQualifiedId", "namespace#person2")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+
+  // Prepare join search spec to join a query for `name:person` with a child
+  // query for `body:message` based on the child's `senderQualifiedId` field.
+  SearchSpecProto search_spec;
+  search_spec.set_term_match_type(TermMatchType::EXACT_ONLY);
+  search_spec.set_query("name:person");
+  JoinSpecProto* join_spec = search_spec.mutable_join_spec();
+  join_spec->set_max_joined_child_count(100);
+  join_spec->set_parent_property_expression(
+      std::string(JoinProcessor::kQualifiedIdExpr));
+  join_spec->set_child_property_expression("senderQualifiedId");
+  join_spec->set_aggregation_scoring_strategy(
+      JoinSpecProto::AggregationScoringStrategy::COUNT);
+  JoinSpecProto::NestedSpecProto* nested_spec =
+      join_spec->mutable_nested_spec();
+  SearchSpecProto* nested_search_spec = nested_spec->mutable_search_spec();
+  nested_search_spec->set_term_match_type(TermMatchType::EXACT_ONLY);
+  nested_search_spec->set_query("body:message");
+  *nested_spec->mutable_scoring_spec() = GetDefaultScoringSpec();
+  *nested_spec->mutable_result_spec() = ResultSpecProto::default_instance();
+
+  // Message1 and message3 are going to be deleted below. Both person1 and
+  // person2 should be included even though person2 has no child (since we're
+  // doing left join).
+  SearchResultProto expected_search_result_proto;
+  expected_search_result_proto.mutable_status()->set_code(StatusProto::OK);
+  SearchResultProto::ResultProto* result_proto1 =
+      expected_search_result_proto.mutable_results()->Add();
+  *result_proto1->mutable_document() = person1;
+  *result_proto1->mutable_joined_results()->Add()->mutable_document() =
+      message2;
+  SearchResultProto::ResultProto* result_google::protobuf =
+      expected_search_result_proto.mutable_results()->Add();
+  *result_google::protobuf->mutable_document() = person2;
+
+  {
+    IcingSearchEngine icing(GetDefaultIcingOptions(), GetTestJniCache());
+    ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
+    ASSERT_THAT(icing.SetSchema(schema).status(), ProtoIsOk());
+    ASSERT_THAT(icing.Put(person1).status(), ProtoIsOk());
+    ASSERT_THAT(icing.Put(person2).status(), ProtoIsOk());
+    ASSERT_THAT(icing.Put(message1).status(), ProtoIsOk());
+    ASSERT_THAT(icing.Put(message2).status(), ProtoIsOk());
+    ASSERT_THAT(icing.Put(message3).status(), ProtoIsOk());
+    // Delete child documents: message1 and message3
+    ASSERT_THAT(icing.Delete("namespace", "message1").status(), ProtoIsOk());
+    ASSERT_THAT(icing.Delete("namespace", "message3").status(), ProtoIsOk());
+    ASSERT_THAT(icing.Optimize().status(), ProtoIsOk());
+
+    // Validates that join search query works right after Optimize()
+    SearchResultProto search_result_proto =
+        icing.Search(search_spec, GetDefaultScoringSpec(),
+                     ResultSpecProto::default_instance());
+    EXPECT_THAT(search_result_proto, EqualsSearchResultIgnoreStatsAndScores(
+                                         expected_search_result_proto));
+  }  // Destroys IcingSearchEngine to make sure nothing is cached.
+
+  IcingSearchEngine icing(GetDefaultIcingOptions(), GetTestJniCache());
+  EXPECT_THAT(icing.Initialize().status(), ProtoIsOk());
+
+  SearchResultProto search_result_proto =
+      icing.Search(search_spec, GetDefaultScoringSpec(),
+                   ResultSpecProto::default_instance());
+  EXPECT_THAT(search_result_proto, EqualsSearchResultIgnoreStatsAndScores(
+                                       expected_search_result_proto));
+}
+
+TEST_F(IcingSearchEngineOptimizeTest,
        IcingShouldWorkFineIfOptimizationIsAborted) {
-  DocumentProto document1 = CreateMessageDocument("namespace", "uri1");
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("Person").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("name")
+                  .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("Message")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("body")
+                                        .SetDataTypeString(TERM_MATCH_PREFIX,
+                                                           TOKENIZER_PLAIN)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("indexableInteger")
+                                        .SetDataTypeInt64(NUMERIC_MATCH_RANGE)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("senderQualifiedId")
+                                        .SetDataTypeJoinableString(
+                                            JOINABLE_VALUE_TYPE_QUALIFIED_ID)
+                                        .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
+  DocumentProto person =
+      DocumentBuilder()
+          .SetKey("namespace", "person")
+          .SetSchema("Person")
+          .AddStringProperty("name", "person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+
+  DocumentProto message1 =
+      DocumentBuilder()
+          .SetKey("namespace", "message1")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body one")
+          .AddInt64Property("indexableInteger", 123)
+          .AddStringProperty("senderQualifiedId", "namespace#person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
   {
     // Initializes a normal icing to create files needed
     IcingSearchEngine icing(GetDefaultIcingOptions(), GetTestJniCache());
     ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
-    ASSERT_THAT(icing.SetSchema(CreateMessageSchema()).status(), ProtoIsOk());
-    ASSERT_THAT(icing.Put(document1).status(), ProtoIsOk());
+    ASSERT_THAT(icing.SetSchema(schema).status(), ProtoIsOk());
+    ASSERT_THAT(icing.Put(person).status(), ProtoIsOk());
+    ASSERT_THAT(icing.Put(message1).status(), ProtoIsOk());
   }
 
   // Creates a mock filesystem in which DeleteDirectoryRecursively() always
@@ -733,25 +1153,33 @@ TEST_F(IcingSearchEngineOptimizeTest,
 
   GetResultProto expected_get_result_proto;
   expected_get_result_proto.mutable_status()->set_code(StatusProto::OK);
-  *expected_get_result_proto.mutable_document() = document1;
-  EXPECT_THAT(
-      icing.Get("namespace", "uri1", GetResultSpecProto::default_instance()),
-      EqualsProto(expected_get_result_proto));
+  *expected_get_result_proto.mutable_document() = message1;
+  EXPECT_THAT(icing.Get("namespace", "message1",
+                        GetResultSpecProto::default_instance()),
+              EqualsProto(expected_get_result_proto));
 
-  DocumentProto document2 = CreateMessageDocument("namespace", "uri2");
+  DocumentProto message2 =
+      DocumentBuilder()
+          .SetKey("namespace", "message2")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body two")
+          .AddInt64Property("indexableInteger", 123)
+          .AddStringProperty("senderQualifiedId", "namespace#person")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
 
-  EXPECT_THAT(icing.Put(document2).status(), ProtoIsOk());
+  EXPECT_THAT(icing.Put(message2).status(), ProtoIsOk());
 
   SearchResultProto expected_search_result_proto;
   expected_search_result_proto.mutable_status()->set_code(StatusProto::OK);
   *expected_search_result_proto.mutable_results()->Add()->mutable_document() =
-      document2;
+      message2;
   *expected_search_result_proto.mutable_results()->Add()->mutable_document() =
-      document1;
+      message1;
 
   // Verify term search
   SearchSpecProto search_spec1;
-  search_spec1.set_query("m");
+  search_spec1.set_query("body:m");
   search_spec1.set_term_match_type(TermMatchType::PREFIX);
 
   SearchResultProto search_result_proto1 =
@@ -772,10 +1200,68 @@ TEST_F(IcingSearchEngineOptimizeTest,
                    ResultSpecProto::default_instance());
   EXPECT_THAT(search_result_google::protobuf, EqualsSearchResultIgnoreStatsAndScores(
                                         expected_search_result_proto));
+
+  // Verify join search: join a query for `name:person` with a child query for
+  // `body:message` based on the child's `senderQualifiedId` field.
+  SearchSpecProto search_spec3;
+  search_spec3.set_term_match_type(TermMatchType::EXACT_ONLY);
+  search_spec3.set_query("name:person");
+  JoinSpecProto* join_spec = search_spec3.mutable_join_spec();
+  join_spec->set_max_joined_child_count(100);
+  join_spec->set_parent_property_expression(
+      std::string(JoinProcessor::kQualifiedIdExpr));
+  join_spec->set_child_property_expression("senderQualifiedId");
+  join_spec->set_aggregation_scoring_strategy(
+      JoinSpecProto::AggregationScoringStrategy::COUNT);
+  JoinSpecProto::NestedSpecProto* nested_spec =
+      join_spec->mutable_nested_spec();
+  SearchSpecProto* nested_search_spec = nested_spec->mutable_search_spec();
+  nested_search_spec->set_term_match_type(TermMatchType::EXACT_ONLY);
+  nested_search_spec->set_query("body:message");
+  *nested_spec->mutable_scoring_spec() = GetDefaultScoringSpec();
+  *nested_spec->mutable_result_spec() = ResultSpecProto::default_instance();
+
+  SearchResultProto expected_join_search_result_proto;
+  expected_join_search_result_proto.mutable_status()->set_code(StatusProto::OK);
+  SearchResultProto::ResultProto* result_proto =
+      expected_join_search_result_proto.mutable_results()->Add();
+  *result_proto->mutable_document() = person;
+  *result_proto->mutable_joined_results()->Add()->mutable_document() = message2;
+  *result_proto->mutable_joined_results()->Add()->mutable_document() = message1;
+
+  SearchResultProto search_result_proto3 =
+      icing.Search(search_spec3, GetDefaultScoringSpec(),
+                   ResultSpecProto::default_instance());
+  EXPECT_THAT(search_result_proto3, EqualsSearchResultIgnoreStatsAndScores(
+                                        expected_join_search_result_proto));
 }
 
 TEST_F(IcingSearchEngineOptimizeTest,
        OptimizationShouldRecoverIfFileDirectoriesAreMissing) {
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("Message")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("body")
+                                        .SetDataTypeString(TERM_MATCH_PREFIX,
+                                                           TOKENIZER_PLAIN)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("indexableInteger")
+                                        .SetDataTypeInt64(NUMERIC_MATCH_RANGE)
+                                        .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
+  DocumentProto document =
+      DocumentBuilder()
+          .SetKey("namespace", "uri1")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body")
+          .AddInt64Property("indexableInteger", 123)
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+
   // Creates a mock filesystem in which SwapFiles() always fails and deletes the
   // directories. This will fail IcingSearchEngine::OptimizeDocumentStore().
   auto mock_filesystem = std::make_unique<MockFilesystem>();
@@ -793,9 +1279,8 @@ TEST_F(IcingSearchEngineOptimizeTest,
                               std::make_unique<FakeClock>(), GetTestJniCache());
 
   ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
-  ASSERT_THAT(icing.SetSchema(CreateMessageSchema()).status(), ProtoIsOk());
-  ASSERT_THAT(icing.Put(CreateMessageDocument("namespace", "uri")).status(),
-              ProtoIsOk());
+  ASSERT_THAT(icing.SetSchema(schema).status(), ProtoIsOk());
+  ASSERT_THAT(icing.Put(document).status(), ProtoIsOk());
 
   // Optimize() fails due to filesystem error
   OptimizeResultProto result = icing.Optimize();
@@ -873,6 +1358,30 @@ TEST_F(IcingSearchEngineOptimizeTest,
 
 TEST_F(IcingSearchEngineOptimizeTest,
        OptimizationShouldRecoverIfDataFilesAreMissing) {
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("Message")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("body")
+                                        .SetDataTypeString(TERM_MATCH_PREFIX,
+                                                           TOKENIZER_PLAIN)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("indexableInteger")
+                                        .SetDataTypeInt64(NUMERIC_MATCH_RANGE)
+                                        .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
+  DocumentProto document =
+      DocumentBuilder()
+          .SetKey("namespace", "uri1")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body")
+          .AddInt64Property("indexableInteger", 123)
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+
   // Creates a mock filesystem in which SwapFiles() always fails and empties the
   // directories. This will fail IcingSearchEngine::OptimizeDocumentStore().
   auto mock_filesystem = std::make_unique<MockFilesystem>();
@@ -892,9 +1401,8 @@ TEST_F(IcingSearchEngineOptimizeTest,
                               std::make_unique<FakeClock>(), GetTestJniCache());
 
   ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
-  ASSERT_THAT(icing.SetSchema(CreateMessageSchema()).status(), ProtoIsOk());
-  ASSERT_THAT(icing.Put(CreateMessageDocument("namespace", "uri")).status(),
-              ProtoIsOk());
+  ASSERT_THAT(icing.SetSchema(schema).status(), ProtoIsOk());
+  ASSERT_THAT(icing.Put(document).status(), ProtoIsOk());
 
   // Optimize() fails due to filesystem error
   OptimizeResultProto result = icing.Optimize();
@@ -969,23 +1477,61 @@ TEST_F(IcingSearchEngineOptimizeTest,
                                         expected_search_result_proto));
 }
 
-TEST_F(IcingSearchEngineOptimizeTest, OptimizeStatsProtoTest) {
+TEST_F(IcingSearchEngineOptimizeTest, OptimizeThresholdTest) {
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("Message")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("body")
+                                        .SetDataTypeString(TERM_MATCH_PREFIX,
+                                                           TOKENIZER_PLAIN)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("indexableInteger")
+                                        .SetDataTypeInt64(NUMERIC_MATCH_RANGE)
+                                        .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
+  DocumentProto document1 =
+      DocumentBuilder()
+          .SetKey("namespace", "uri1")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body one")
+          .AddInt64Property("indexableInteger", 1)
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto document2 = DocumentBuilder()
+                                .SetKey("namespace", "uri2")
+                                .SetSchema("Message")
+                                .AddStringProperty("body", "message body two")
+                                .AddInt64Property("indexableInteger", 2)
+                                .SetCreationTimestampMs(9000)
+                                .SetTtlMs(500)
+                                .Build();
+  DocumentProto document3 =
+      DocumentBuilder()
+          .SetKey("namespace", "uri3")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body three")
+          .AddInt64Property("indexableInteger", 3)
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+
   auto fake_clock = std::make_unique<FakeClock>();
   fake_clock->SetTimerElapsedMilliseconds(5);
   fake_clock->SetSystemTimeMilliseconds(10000);
+  IcingSearchEngineOptions options = GetDefaultIcingOptions();
+  // Set the threshold to 0.9 to test that the threshold works.
+  options.set_optimize_rebuild_index_threshold(0.9);
   auto icing = std::make_unique<TestIcingSearchEngine>(
-      GetDefaultIcingOptions(), std::make_unique<Filesystem>(),
+      options, std::make_unique<Filesystem>(),
       std::make_unique<IcingFilesystem>(), std::move(fake_clock),
       GetTestJniCache());
   ASSERT_THAT(icing->Initialize().status(), ProtoIsOk());
-  ASSERT_THAT(icing->SetSchema(CreateMessageSchema()).status(), ProtoIsOk());
-
-  // Create three documents.
-  DocumentProto document1 = CreateMessageDocument("namespace", "uri1");
-  DocumentProto document2 = CreateMessageDocument("namespace", "uri2");
-  document2.set_creation_timestamp_ms(9000);
-  document2.set_ttl_ms(500);
-  DocumentProto document3 = CreateMessageDocument("namespace", "uri3");
+  ASSERT_THAT(icing->SetSchema(schema).status(), ProtoIsOk());
+
+  // Add three documents.
   ASSERT_THAT(icing->Put(document1).status(), ProtoIsOk());
   ASSERT_THAT(icing->Put(document2).status(), ProtoIsOk());
   ASSERT_THAT(icing->Put(document3).status(), ProtoIsOk());
@@ -1022,7 +1568,7 @@ TEST_F(IcingSearchEngineOptimizeTest, OptimizeStatsProtoTest) {
   fake_clock->SetTimerElapsedMilliseconds(5);
   fake_clock->SetSystemTimeMilliseconds(20000);
   icing = std::make_unique<TestIcingSearchEngine>(
-      GetDefaultIcingOptions(), std::make_unique<Filesystem>(),
+      options, std::make_unique<Filesystem>(),
       std::make_unique<IcingFilesystem>(), std::move(fake_clock),
       GetTestJniCache());
   ASSERT_THAT(icing->Initialize().status(), ProtoIsOk());
@@ -1069,6 +1615,144 @@ TEST_F(IcingSearchEngineOptimizeTest, OptimizeStatsProtoTest) {
   EXPECT_THAT(result.optimize_stats(), EqualsProto(expected));
 }
 
+TEST_F(IcingSearchEngineOptimizeTest, OptimizeStatsProtoTest) {
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("Message")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("body")
+                                        .SetDataTypeString(TERM_MATCH_PREFIX,
+                                                           TOKENIZER_PLAIN)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("indexableInteger")
+                                        .SetDataTypeInt64(NUMERIC_MATCH_RANGE)
+                                        .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
+  DocumentProto document1 =
+      DocumentBuilder()
+          .SetKey("namespace", "uri1")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body one")
+          .AddInt64Property("indexableInteger", 1)
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto document2 = DocumentBuilder()
+                                .SetKey("namespace", "uri2")
+                                .SetSchema("Message")
+                                .AddStringProperty("body", "message body two")
+                                .AddInt64Property("indexableInteger", 2)
+                                .SetCreationTimestampMs(9000)
+                                .SetTtlMs(500)
+                                .Build();
+  DocumentProto document3 =
+      DocumentBuilder()
+          .SetKey("namespace", "uri3")
+          .SetSchema("Message")
+          .AddStringProperty("body", "message body three")
+          .AddInt64Property("indexableInteger", 3)
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+
+  auto fake_clock = std::make_unique<FakeClock>();
+  fake_clock->SetTimerElapsedMilliseconds(5);
+  fake_clock->SetSystemTimeMilliseconds(10000);
+  // Use the default Icing options, so that a change to the default value will
+  // require updating this test.
+  auto icing = std::make_unique<TestIcingSearchEngine>(
+      GetDefaultIcingOptions(), std::make_unique<Filesystem>(),
+      std::make_unique<IcingFilesystem>(), std::move(fake_clock),
+      GetTestJniCache());
+  ASSERT_THAT(icing->Initialize().status(), ProtoIsOk());
+  ASSERT_THAT(icing->SetSchema(schema).status(), ProtoIsOk());
+
+  // Add three documents.
+  ASSERT_THAT(icing->Put(document1).status(), ProtoIsOk());
+  ASSERT_THAT(icing->Put(document2).status(), ProtoIsOk());
+  ASSERT_THAT(icing->Put(document3).status(), ProtoIsOk());
+
+  // Delete the first document.
+  ASSERT_THAT(icing->Delete(document1.namespace_(), document1.uri()).status(),
+              ProtoIsOk());
+  ASSERT_THAT(icing->PersistToDisk(PersistType::FULL).status(), ProtoIsOk());
+
+  OptimizeStatsProto expected;
+  expected.set_latency_ms(5);
+  expected.set_document_store_optimize_latency_ms(5);
+  expected.set_index_restoration_latency_ms(5);
+  expected.set_num_original_documents(3);
+  expected.set_num_deleted_documents(1);
+  expected.set_num_expired_documents(1);
+  expected.set_index_restoration_mode(OptimizeStatsProto::FULL_INDEX_REBUILD);
+
+  // Run Optimize
+  OptimizeResultProto result = icing->Optimize();
+  // Depending on how many blocks the documents end up spread across, it's
+  // possible that Optimize can remove documents without shrinking storage. The
+  // first Optimize call will also write the OptimizeStatusProto for the first
+  // time which will take up 1 block. So make sure that before_size is no less
+  // than after_size - 1 block.
+  uint32_t page_size = getpagesize();
+  EXPECT_THAT(result.optimize_stats().storage_size_before(),
+              Ge(result.optimize_stats().storage_size_after() - page_size));
+  result.mutable_optimize_stats()->clear_storage_size_before();
+  result.mutable_optimize_stats()->clear_storage_size_after();
+  EXPECT_THAT(result.optimize_stats(), EqualsProto(expected));
+
+  fake_clock = std::make_unique<FakeClock>();
+  fake_clock->SetTimerElapsedMilliseconds(5);
+  fake_clock->SetSystemTimeMilliseconds(20000);
+  // Use the default Icing options, so that a change to the default value will
+  // require updating this test.
+  icing = std::make_unique<TestIcingSearchEngine>(
+      GetDefaultIcingOptions(), std::make_unique<Filesystem>(),
+      std::make_unique<IcingFilesystem>(), std::move(fake_clock),
+      GetTestJniCache());
+  ASSERT_THAT(icing->Initialize().status(), ProtoIsOk());
+
+  expected = OptimizeStatsProto();
+  expected.set_latency_ms(5);
+  expected.set_document_store_optimize_latency_ms(5);
+  expected.set_index_restoration_latency_ms(5);
+  expected.set_num_original_documents(1);
+  expected.set_num_deleted_documents(0);
+  expected.set_num_expired_documents(0);
+  expected.set_time_since_last_optimize_ms(10000);
+  expected.set_index_restoration_mode(OptimizeStatsProto::FULL_INDEX_REBUILD);
+
+  // Run Optimize
+  result = icing->Optimize();
+  EXPECT_THAT(result.optimize_stats().storage_size_before(),
+              Eq(result.optimize_stats().storage_size_after()));
+  result.mutable_optimize_stats()->clear_storage_size_before();
+  result.mutable_optimize_stats()->clear_storage_size_after();
+  EXPECT_THAT(result.optimize_stats(), EqualsProto(expected));
+
+  // Delete the last document.
+  ASSERT_THAT(icing->Delete(document3.namespace_(), document3.uri()).status(),
+              ProtoIsOk());
+
+  expected = OptimizeStatsProto();
+  expected.set_latency_ms(5);
+  expected.set_document_store_optimize_latency_ms(5);
+  expected.set_index_restoration_latency_ms(5);
+  expected.set_num_original_documents(1);
+  expected.set_num_deleted_documents(1);
+  expected.set_num_expired_documents(0);
+  expected.set_time_since_last_optimize_ms(0);
+  expected.set_index_restoration_mode(OptimizeStatsProto::FULL_INDEX_REBUILD);
+
+  // Run Optimize
+  result = icing->Optimize();
+  EXPECT_THAT(result.optimize_stats().storage_size_before(),
+              Ge(result.optimize_stats().storage_size_after()));
+  result.mutable_optimize_stats()->clear_storage_size_before();
+  result.mutable_optimize_stats()->clear_storage_size_after();
+  EXPECT_THAT(result.optimize_stats(), EqualsProto(expected));
+}
+
 }  // namespace
 }  // namespace lib
 }  // namespace icing
diff --git a/icing/icing-search-engine_schema_test.cc b/icing/icing-search-engine_schema_test.cc
index 38a0464..7081ba2 100644
--- a/icing/icing-search-engine_schema_test.cc
+++ b/icing/icing-search-engine_schema_test.cc
@@ -26,6 +26,7 @@
 #include "icing/file/mock-filesystem.h"
 #include "icing/icing-search-engine.h"
 #include "icing/jni/jni-cache.h"
+#include "icing/join/join-processor.h"
 #include "icing/portable/endian.h"
 #include "icing/portable/equals-proto.h"
 #include "icing/portable/platform.h"
@@ -153,6 +154,10 @@ ScoringSpecProto GetDefaultScoringSpec() {
   return scoring_spec;
 }
 
+// TODO(b/272145329): create SearchSpecBuilder, JoinSpecBuilder,
+// SearchResultProtoBuilder and ResultProtoBuilder for unit tests and build all
+// instances by them.
+
 TEST_F(IcingSearchEngineSchemaTest,
        CircularReferenceCreateSectionManagerReturnsInvalidArgument) {
   // Create a type config with a circular reference.
@@ -1077,7 +1082,203 @@ TEST_F(IcingSearchEngineSchemaTest,
 }
 
 TEST_F(IcingSearchEngineSchemaTest,
-       ForceSetSchemaPropertyDeletionTriggersIndexRestorationAndReturnsOk) {
+       SetSchemaNewJoinablePropertyTriggersIndexRestorationAndReturnsOk) {
+  IcingSearchEngine icing(GetDefaultIcingOptions(), GetTestJniCache());
+  ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
+
+  // Create "Message" schema with 3 properties:
+  // - "subject": string type, non-joinable. No joinable property id assigned.
+  //   It is indexed and used for searching only.
+  // - "receiverQualifiedId": string type, non-joinable. No joinable property id
+  //   assigned.
+  // - "senderQualifiedId": string type, Qualified Id type joinable. Joinable
+  //   property id = 0.
+  SchemaProto schema_one =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("Person").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("name")
+                  .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("Message")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("subject")
+                                        .SetDataTypeString(TERM_MATCH_PREFIX,
+                                                           TOKENIZER_PLAIN)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("receiverQualifiedId")
+                                        .SetDataTypeJoinableString(
+                                            JOINABLE_VALUE_TYPE_NONE)
+                                        .SetCardinality(CARDINALITY_REQUIRED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("senderQualifiedId")
+                                        .SetDataTypeJoinableString(
+                                            JOINABLE_VALUE_TYPE_QUALIFIED_ID)
+                                        .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
+  SetSchemaResultProto set_schema_result = icing.SetSchema(schema_one);
+  // Ignore latency numbers. They're covered elsewhere.
+  set_schema_result.clear_latency_ms();
+  SetSchemaResultProto expected_set_schema_result;
+  expected_set_schema_result.mutable_status()->set_code(StatusProto::OK);
+  expected_set_schema_result.mutable_new_schema_types()->Add("Message");
+  expected_set_schema_result.mutable_new_schema_types()->Add("Person");
+  EXPECT_THAT(set_schema_result, EqualsProto(expected_set_schema_result));
+
+  DocumentProto person1 =
+      DocumentBuilder()
+          .SetKey("namespace", "person1")
+          .SetSchema("Person")
+          .AddStringProperty("name", "person one")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+  DocumentProto person2 =
+      DocumentBuilder()
+          .SetKey("namespace", "person2")
+          .SetSchema("Person")
+          .AddStringProperty("name", "person two")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+
+  DocumentProto message =
+      DocumentBuilder()
+          .SetKey("namespace", "message1")
+          .SetSchema("Message")
+          .AddStringProperty("subject", "message")
+          .AddStringProperty("receiverQualifiedId", "namespace#person1")
+          .AddStringProperty("senderQualifiedId", "namespace#person2")
+          .SetCreationTimestampMs(kDefaultCreationTimestampMs)
+          .Build();
+
+  EXPECT_THAT(icing.Put(person1).status(), ProtoIsOk());
+  EXPECT_THAT(icing.Put(person2).status(), ProtoIsOk());
+  EXPECT_THAT(icing.Put(message).status(), ProtoIsOk());
+
+  // Verify join search: join a query for `name:person` with a child query for
+  // `subject:message` based on the child's `receiverQualifiedId` field.
+  // Since "receiverQualifiedId" is not JOINABLE_VALUE_TYPE_QUALIFIED_ID,
+  // joining on that property should only return the "left-side" (`name:person`)
+  // of the join.
+  SearchSpecProto search_spec_join_by_receiver;
+  search_spec_join_by_receiver.set_query("name:person");
+  search_spec_join_by_receiver.set_term_match_type(TermMatchType::EXACT_ONLY);
+  JoinSpecProto* join_spec = search_spec_join_by_receiver.mutable_join_spec();
+  join_spec->set_max_joined_child_count(100);
+  join_spec->set_parent_property_expression(
+      std::string(JoinProcessor::kQualifiedIdExpr));
+  join_spec->set_child_property_expression("receiverQualifiedId");
+  join_spec->set_aggregation_scoring_strategy(
+      JoinSpecProto::AggregationScoringStrategy::COUNT);
+  JoinSpecProto::NestedSpecProto* nested_spec =
+      join_spec->mutable_nested_spec();
+  SearchSpecProto* nested_search_spec = nested_spec->mutable_search_spec();
+  nested_search_spec->set_term_match_type(TermMatchType::EXACT_ONLY);
+  nested_search_spec->set_query("subject:message");
+  *nested_spec->mutable_scoring_spec() = GetDefaultScoringSpec();
+  *nested_spec->mutable_result_spec() = ResultSpecProto::default_instance();
+
+  SearchResultProto expected_empty_child_search_result_proto;
+  expected_empty_child_search_result_proto.mutable_status()->set_code(
+      StatusProto::OK);
+  *expected_empty_child_search_result_proto.mutable_results()
+       ->Add()
+       ->mutable_document() = person2;
+  *expected_empty_child_search_result_proto.mutable_results()
+       ->Add()
+       ->mutable_document() = person1;
+  SearchResultProto actual_results =
+      icing.Search(search_spec_join_by_receiver, GetDefaultScoringSpec(),
+                   ResultSpecProto::default_instance());
+  EXPECT_THAT(actual_results, EqualsSearchResultIgnoreStatsAndScores(
+                                  expected_empty_child_search_result_proto));
+
+  // Verify join search: join a query for `name:person` with a child query for
+  // `subject:message` based on the child's `senderQualifiedId` field.
+  // Since "senderQualifiedId" is JOINABLE_VALUE_TYPE_QUALIFIED_ID, joining on
+  // that property should return both "left-side" (`name:person`) and
+  // "right-side" (`subject:message`) of the join.
+  SearchSpecProto search_spec_join_by_sender = search_spec_join_by_receiver;
+  join_spec = search_spec_join_by_sender.mutable_join_spec();
+  join_spec->set_child_property_expression("senderQualifiedId");
+
+  SearchResultProto expected_join_by_sender_search_result_proto;
+  expected_join_by_sender_search_result_proto.mutable_status()->set_code(
+      StatusProto::OK);
+  SearchResultProto::ResultProto* result_proto =
+      expected_join_by_sender_search_result_proto.mutable_results()->Add();
+  *result_proto->mutable_document() = person2;
+  *result_proto->mutable_joined_results()->Add()->mutable_document() = message;
+  *expected_join_by_sender_search_result_proto.mutable_results()
+       ->Add()
+       ->mutable_document() = person1;
+  actual_results =
+      icing.Search(search_spec_join_by_sender, GetDefaultScoringSpec(),
+                   ResultSpecProto::default_instance());
+  EXPECT_THAT(actual_results, EqualsSearchResultIgnoreStatsAndScores(
+                                  expected_join_by_sender_search_result_proto));
+
+  // Change "Message" schema to:
+  // - "subject": string type, non-joinable. No joinable property id assigned.
+  // - "receiverQualifiedId": string type, Qualified Id joinable. Joinable
+  //   property id = 0.
+  // - "senderQualifiedId": string type, Qualified Id joinable. Joinable
+  //   property id = 1.
+  SchemaProto schema_two = schema_one;
+  schema_two.mutable_types(1)
+      ->mutable_properties(1)
+      ->mutable_joinable_config()
+      ->set_value_type(JOINABLE_VALUE_TYPE_QUALIFIED_ID);
+  // Index restoration should be triggered here because new schema requires more
+  // joinable properties. Also new joinable property ids will be reassigned and
+  // index restoration should use new joinable property ids to rebuild.
+  set_schema_result = icing.SetSchema(schema_two);
+  // Ignore latency numbers. They're covered elsewhere.
+  set_schema_result.clear_latency_ms();
+  expected_set_schema_result = SetSchemaResultProto();
+  expected_set_schema_result.mutable_status()->set_code(StatusProto::OK);
+  expected_set_schema_result.mutable_join_incompatible_changed_schema_types()
+      ->Add("Message");
+  EXPECT_THAT(set_schema_result, EqualsProto(expected_set_schema_result));
+
+  // Verify join search: join a query for `name:person` with a child query for
+  // `subject:message` based on the child's `receiverQualifiedId` field.
+  // Since we've changed "receiverQualifiedId" to be
+  // JOINABLE_VALUE_TYPE_QUALIFIED_ID, joining on that property should return
+  // should return both "left-side" (`name:person`) and "right-side"
+  // (`subject:message`) of the join now.
+  SearchResultProto expected_join_by_receiver_search_result_proto;
+  expected_join_by_receiver_search_result_proto.mutable_status()->set_code(
+      StatusProto::OK);
+  result_proto =
+      expected_join_by_receiver_search_result_proto.mutable_results()->Add();
+  *result_proto->mutable_document() = person1;
+  *result_proto->mutable_joined_results()->Add()->mutable_document() = message;
+  *expected_join_by_receiver_search_result_proto.mutable_results()
+       ->Add()
+       ->mutable_document() = person2;
+  actual_results =
+      icing.Search(search_spec_join_by_receiver, GetDefaultScoringSpec(),
+                   ResultSpecProto::default_instance());
+  EXPECT_THAT(actual_results,
+              EqualsSearchResultIgnoreStatsAndScores(
+                  expected_join_by_receiver_search_result_proto));
+
+  // Verify join search: join a query for `name:person` with a child query for
+  // `subject:message` based on the child's `senderQualifiedId` field. We should
+  // get the same set of result since `senderQualifiedId` is unchanged.
+  actual_results =
+      icing.Search(search_spec_join_by_sender, GetDefaultScoringSpec(),
+                   ResultSpecProto::default_instance());
+  EXPECT_THAT(actual_results, EqualsSearchResultIgnoreStatsAndScores(
+                                  expected_join_by_sender_search_result_proto));
+}
+
+TEST_F(
+    IcingSearchEngineSchemaTest,
+    ForceSetSchemaIndexedPropertyDeletionTriggersIndexRestorationAndReturnsOk) {
   IcingSearchEngine icing(GetDefaultIcingOptions(), GetTestJniCache());
   ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
 
@@ -1221,9 +1422,161 @@ TEST_F(IcingSearchEngineSchemaTest,
                                   expected_search_result_proto));
 }
 
+TEST_F(IcingSearchEngineSchemaTest,
+       ForceSetSchemaJoinablePropertyDeletionTriggersIndexRestoration) {
+  IcingSearchEngine icing(GetDefaultIcingOptions(), GetTestJniCache());
+  ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
+
+  // Create "Email" schema with 2 joinable properties:
+  // - "receiverQualifiedId": qualified id joinable. Joinable property id = 0.
+  // - "senderQualifiedId": qualified id joinable. Joinable property id = 1.
+  SchemaProto email_with_receiver_schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("Person").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("name")
+                  .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("Email")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("subject")
+                                        .SetDataTypeString(TERM_MATCH_PREFIX,
+                                                           TOKENIZER_PLAIN)
+                                        .SetCardinality(CARDINALITY_OPTIONAL))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("receiverQualifiedId")
+                                        .SetDataTypeJoinableString(
+                                            JOINABLE_VALUE_TYPE_QUALIFIED_ID)
+                                        .SetCardinality(CARDINALITY_OPTIONAL))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("senderQualifiedId")
+                                        .SetDataTypeJoinableString(
+                                            JOINABLE_VALUE_TYPE_QUALIFIED_ID)
+                                        .SetCardinality(CARDINALITY_OPTIONAL)))
+          .Build();
+
+  SetSchemaResultProto set_schema_result =
+      icing.SetSchema(email_with_receiver_schema);
+  // Ignore latency numbers. They're covered elsewhere.
+  set_schema_result.clear_latency_ms();
+  SetSchemaResultProto expected_set_schema_result;
+  expected_set_schema_result.mutable_new_schema_types()->Add("Email");
+  expected_set_schema_result.mutable_new_schema_types()->Add("Person");
+  expected_set_schema_result.mutable_status()->set_code(StatusProto::OK);
+  EXPECT_THAT(set_schema_result, EqualsProto(expected_set_schema_result));
+
+  DocumentProto person = DocumentBuilder()
+                             .SetKey("namespace", "person")
+                             .SetSchema("Person")
+                             .SetCreationTimestampMs(1000)
+                             .AddStringProperty("name", "person")
+                             .Build();
+  // Create an email document with only "senderQualifiedId" joinable property.
+  DocumentProto email =
+      DocumentBuilder()
+          .SetKey("namespace", "email")
+          .SetSchema("Email")
+          .SetCreationTimestampMs(1000)
+          .AddStringProperty("subject",
+                             "Did you get the memo about TPS reports?")
+          .AddStringProperty("senderQualifiedId", "namespace#person")
+          .Build();
+
+  EXPECT_THAT(icing.Put(person).status(), ProtoIsOk());
+  EXPECT_THAT(icing.Put(email).status(), ProtoIsOk());
+
+  // Verify join search: join a query for `name:person` with a child query for
+  // `subject:tps` based on the child's `senderQualifiedId` field. We should be
+  // able to join person and email documents by this property.
+  SearchResultProto expected_search_result_proto;
+  expected_search_result_proto.mutable_status()->set_code(StatusProto::OK);
+  SearchResultProto::ResultProto* result_proto =
+      expected_search_result_proto.mutable_results()->Add();
+  *result_proto->mutable_document() = person;
+  *result_proto->mutable_joined_results()->Add()->mutable_document() = email;
+
+  SearchSpecProto search_spec;
+  search_spec.set_query("name:person");
+  search_spec.set_term_match_type(TermMatchType::EXACT_ONLY);
+  JoinSpecProto* join_spec = search_spec.mutable_join_spec();
+  join_spec->set_max_joined_child_count(100);
+  join_spec->set_parent_property_expression(
+      std::string(JoinProcessor::kQualifiedIdExpr));
+  join_spec->set_child_property_expression("senderQualifiedId");
+  join_spec->set_aggregation_scoring_strategy(
+      JoinSpecProto::AggregationScoringStrategy::COUNT);
+  JoinSpecProto::NestedSpecProto* nested_spec =
+      join_spec->mutable_nested_spec();
+  SearchSpecProto* nested_search_spec = nested_spec->mutable_search_spec();
+  nested_search_spec->set_term_match_type(TermMatchType::EXACT_ONLY);
+  nested_search_spec->set_query("subject:tps");
+  *nested_spec->mutable_scoring_spec() = GetDefaultScoringSpec();
+  *nested_spec->mutable_result_spec() = ResultSpecProto::default_instance();
+
+  SearchResultProto actual_results =
+      icing.Search(search_spec, GetDefaultScoringSpec(),
+                   ResultSpecProto::default_instance());
+  EXPECT_THAT(actual_results, EqualsSearchResultIgnoreStatsAndScores(
+                                  expected_search_result_proto));
+
+  // Now update the schema to remove "receiverQualifiedId" fields. This is
+  // backwards incompatible, but document should be preserved because it doesn't
+  // contain "receiverQualifiedId" field. Also since it is join incompatible, we
+  // have to rebuild join index.
+  // - "senderQualifiedId": qualified id joinable. Joinable property id = 0.
+  //
+  // If the index is not correctly rebuilt, then the joinable data of
+  // "senderQualifiedId" in the joinable index will still have old joinable
+  // property id of 1 and therefore won't take effect for join search query.
+  SchemaProto email_without_receiver_schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("Person").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("name")
+                  .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("Email")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("subject")
+                                        .SetDataTypeString(TERM_MATCH_PREFIX,
+                                                           TOKENIZER_PLAIN)
+                                        .SetCardinality(CARDINALITY_OPTIONAL))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("senderQualifiedId")
+                                        .SetDataTypeJoinableString(
+                                            JOINABLE_VALUE_TYPE_QUALIFIED_ID)
+                                        .SetCardinality(CARDINALITY_OPTIONAL)))
+          .Build();
+
+  // Although we've just deleted an existing property "receiverQualifiedId" from
+  // schema "Email", some email documents will still be preserved because they
+  // don't have "receiverQualifiedId" property.
+  set_schema_result =
+      icing.SetSchema(email_without_receiver_schema,
+                      /*ignore_errors_and_delete_documents=*/true);
+  // Ignore latency numbers. They're covered elsewhere.
+  set_schema_result.clear_latency_ms();
+  expected_set_schema_result = SetSchemaResultProto();
+  expected_set_schema_result.mutable_incompatible_schema_types()->Add("Email");
+  expected_set_schema_result.mutable_join_incompatible_changed_schema_types()
+      ->Add("Email");
+  expected_set_schema_result.mutable_status()->set_code(StatusProto::OK);
+  EXPECT_THAT(set_schema_result, EqualsProto(expected_set_schema_result));
+
+  // Verify join search: join a query for `name:person` with a child query for
+  // `subject:tps` based on the child's `senderQualifiedId` field. We should
+  // still be able to join person and email documents by this property.
+  actual_results = icing.Search(search_spec, GetDefaultScoringSpec(),
+                                ResultSpecProto::default_instance());
+  EXPECT_THAT(actual_results, EqualsSearchResultIgnoreStatsAndScores(
+                                  expected_search_result_proto));
+}
+
 TEST_F(
     IcingSearchEngineSchemaTest,
-    ForceSetSchemaPropertyDeletionAndAdditionTriggersIndexRestorationAndReturnsOk) {
+    ForceSetSchemaIndexedPropertyDeletionAndAdditionTriggersIndexRestorationAndReturnsOk) {
   IcingSearchEngine icing(GetDefaultIcingOptions(), GetTestJniCache());
   ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
 
@@ -1368,6 +1721,161 @@ TEST_F(
                                   expected_search_result_proto));
 }
 
+TEST_F(
+    IcingSearchEngineSchemaTest,
+    ForceSetSchemaJoinablePropertyDeletionAndAdditionTriggersIndexRestorationAndReturnsOk) {
+  IcingSearchEngine icing(GetDefaultIcingOptions(), GetTestJniCache());
+  ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
+
+  // Create "Email" schema with 2 joinable properties:
+  // - "receiverQualifiedId": qualified id joinable. Joinable property id = 0.
+  // - "senderQualifiedId": qualified id joinable. Joinable property id = 1.
+  SchemaProto email_with_body_schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("Person").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("name")
+                  .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("Email")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("subject")
+                                        .SetDataTypeString(TERM_MATCH_PREFIX,
+                                                           TOKENIZER_PLAIN)
+                                        .SetCardinality(CARDINALITY_OPTIONAL))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("receiverQualifiedId")
+                                        .SetDataTypeJoinableString(
+                                            JOINABLE_VALUE_TYPE_QUALIFIED_ID)
+                                        .SetCardinality(CARDINALITY_OPTIONAL))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("senderQualifiedId")
+                                        .SetDataTypeJoinableString(
+                                            JOINABLE_VALUE_TYPE_QUALIFIED_ID)
+                                        .SetCardinality(CARDINALITY_OPTIONAL)))
+          .Build();
+
+  SetSchemaResultProto set_schema_result =
+      icing.SetSchema(email_with_body_schema);
+  // Ignore latency numbers. They're covered elsewhere.
+  set_schema_result.clear_latency_ms();
+  SetSchemaResultProto expected_set_schema_result;
+  expected_set_schema_result.mutable_new_schema_types()->Add("Email");
+  expected_set_schema_result.mutable_new_schema_types()->Add("Person");
+  expected_set_schema_result.mutable_status()->set_code(StatusProto::OK);
+  EXPECT_THAT(set_schema_result, EqualsProto(expected_set_schema_result));
+
+  DocumentProto person = DocumentBuilder()
+                             .SetKey("namespace", "person")
+                             .SetSchema("Person")
+                             .SetCreationTimestampMs(1000)
+                             .AddStringProperty("name", "person")
+                             .Build();
+  // Create an email document with only subject and timestamp property.
+  DocumentProto email =
+      DocumentBuilder()
+          .SetKey("namespace", "email")
+          .SetSchema("Email")
+          .SetCreationTimestampMs(1000)
+          .AddStringProperty("subject",
+                             "Did you get the memo about TPS reports?")
+          .AddStringProperty("senderQualifiedId", "namespace#person")
+          .Build();
+
+  EXPECT_THAT(icing.Put(person).status(), ProtoIsOk());
+  EXPECT_THAT(icing.Put(email).status(), ProtoIsOk());
+
+  // Verify join search: join a query for `name:person` with a child query for
+  // `subject:tps` based on the child's `senderQualifiedId` field. We should be
+  // able to join person and email documents by this property.
+  SearchResultProto expected_search_result_proto;
+  expected_search_result_proto.mutable_status()->set_code(StatusProto::OK);
+  SearchResultProto::ResultProto* result_proto =
+      expected_search_result_proto.mutable_results()->Add();
+  *result_proto->mutable_document() = person;
+  *result_proto->mutable_joined_results()->Add()->mutable_document() = email;
+
+  SearchSpecProto search_spec;
+  search_spec.set_query("name:person");
+  search_spec.set_term_match_type(TermMatchType::EXACT_ONLY);
+  JoinSpecProto* join_spec = search_spec.mutable_join_spec();
+  join_spec->set_max_joined_child_count(100);
+  join_spec->set_parent_property_expression(
+      std::string(JoinProcessor::kQualifiedIdExpr));
+  join_spec->set_child_property_expression("senderQualifiedId");
+  join_spec->set_aggregation_scoring_strategy(
+      JoinSpecProto::AggregationScoringStrategy::COUNT);
+  JoinSpecProto::NestedSpecProto* nested_spec =
+      join_spec->mutable_nested_spec();
+  SearchSpecProto* nested_search_spec = nested_spec->mutable_search_spec();
+  nested_search_spec->set_term_match_type(TermMatchType::EXACT_ONLY);
+  nested_search_spec->set_query("subject:tps");
+  *nested_spec->mutable_scoring_spec() = GetDefaultScoringSpec();
+  *nested_spec->mutable_result_spec() = ResultSpecProto::default_instance();
+
+  SearchResultProto actual_results =
+      icing.Search(search_spec, GetDefaultScoringSpec(),
+                   ResultSpecProto::default_instance());
+  EXPECT_THAT(actual_results, EqualsSearchResultIgnoreStatsAndScores(
+                                  expected_search_result_proto));
+
+  // Now update the schema to remove the "receiverQualified" field and add
+  // "zQualifiedId". This is backwards incompatible, but document should
+  // be preserved because it doesn't contain a "receiverQualified" field and
+  // "zQualifiedId" is optional.
+  // - "senderQualifiedId": qualified id joinable. Joinable property id = 0.
+  // - "zQualifiedId": qualified id joinable. Joinable property id = 1.
+  //
+  // If the index is not correctly rebuilt, then the joinable data of
+  // "senderQualifiedId" in the joinable index will still have old joinable
+  // property id of 1 and therefore won't take effect for join search query.
+  SchemaProto email_no_body_schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("Person").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("name")
+                  .SetDataTypeString(TERM_MATCH_PREFIX, TOKENIZER_PLAIN)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("Email")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("subject")
+                                        .SetDataTypeString(TERM_MATCH_PREFIX,
+                                                           TOKENIZER_PLAIN)
+                                        .SetCardinality(CARDINALITY_OPTIONAL))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("zQualifiedId")
+                                        .SetDataTypeJoinableString(
+                                            JOINABLE_VALUE_TYPE_QUALIFIED_ID)
+                                        .SetCardinality(CARDINALITY_OPTIONAL))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("senderQualifiedId")
+                                        .SetDataTypeJoinableString(
+                                            JOINABLE_VALUE_TYPE_QUALIFIED_ID)
+                                        .SetCardinality(CARDINALITY_OPTIONAL)))
+          .Build();
+
+  set_schema_result = icing.SetSchema(
+      email_no_body_schema, /*ignore_errors_and_delete_documents=*/true);
+  // Ignore latency numbers. They're covered elsewhere.
+  set_schema_result.clear_latency_ms();
+  expected_set_schema_result = SetSchemaResultProto();
+  expected_set_schema_result.mutable_incompatible_schema_types()->Add("Email");
+  expected_set_schema_result.mutable_join_incompatible_changed_schema_types()
+      ->Add("Email");
+  expected_set_schema_result.mutable_status()->set_code(StatusProto::OK);
+  EXPECT_THAT(set_schema_result, EqualsProto(expected_set_schema_result));
+
+  // Verify join search: join a query for `name:person` with a child query for
+  // `subject:tps` based on the child's `senderQualifiedId` field. We should
+  // still be able to join person and email documents by this property.
+  actual_results = icing.Search(search_spec, GetDefaultScoringSpec(),
+                                ResultSpecProto::default_instance());
+  EXPECT_THAT(actual_results, EqualsSearchResultIgnoreStatsAndScores(
+                                  expected_search_result_proto));
+}
+
 TEST_F(IcingSearchEngineSchemaTest,
        ForceSetSchemaIncompatibleNestedDocsAreDeleted) {
   IcingSearchEngine icing(GetDefaultIcingOptions(), GetTestJniCache());
@@ -1485,9 +1993,6 @@ TEST_F(IcingSearchEngineSchemaTest,
   EXPECT_THAT(get_result.status(), ProtoStatusIs(StatusProto::NOT_FOUND));
 }
 
-// TODO(b/256022027): add unit tests for join incompatible schema change to make
-//   sure the joinable cache is rebuilt correctly.
-
 TEST_F(IcingSearchEngineSchemaTest, SetSchemaRevalidatesDocumentsAndReturnsOk) {
   IcingSearchEngine icing(GetDefaultIcingOptions(), GetTestJniCache());
   ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
diff --git a/icing/icing-search-engine_search_test.cc b/icing/icing-search-engine_search_test.cc
index 5648184..e953d71 100644
--- a/icing/icing-search-engine_search_test.cc
+++ b/icing/icing-search-engine_search_test.cc
@@ -4388,6 +4388,96 @@ TEST_P(IcingSearchEngineSearchTest, LatinSnippetTest) {
   ASSERT_THAT(match, Eq("ḞÖÖ"));
 }
 
+TEST_P(IcingSearchEngineSearchTest,
+       DocumentStoreNamespaceIdFingerprintCompatible) {
+  DocumentProto document1 = CreateMessageDocument("namespace", "uri1");
+  DocumentProto document2 = CreateMessageDocument("namespace", "uri2");
+  DocumentProto document3 = CreateMessageDocument("namespace", "uri3");
+
+  // Initialize with some documents with document_store_namespace_id_fingerprint
+  // being false.
+  {
+    IcingSearchEngineOptions options = GetDefaultIcingOptions();
+    options.set_document_store_namespace_id_fingerprint(false);
+    IcingSearchEngine icing(options, GetTestJniCache());
+    ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
+    ASSERT_THAT(icing.SetSchema(CreateMessageSchema()).status(), ProtoIsOk());
+
+    // Creates and inserts 3 documents
+    ASSERT_THAT(icing.Put(document1).status(), ProtoIsOk());
+    ASSERT_THAT(icing.Put(document2).status(), ProtoIsOk());
+    ASSERT_THAT(icing.Put(document3).status(), ProtoIsOk());
+  }
+
+  // Reinitializate with document_store_namespace_id_fingerprint being true,
+  // and test that we are still able to read/query docs.
+  {
+    IcingSearchEngineOptions options = GetDefaultIcingOptions();
+    options.set_document_store_namespace_id_fingerprint(true);
+    IcingSearchEngine icing(options, GetTestJniCache());
+    ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
+
+    ASSERT_THAT(
+        icing.Get("namespace", "uri1", GetResultSpecProto::default_instance())
+            .status(),
+        ProtoIsOk());
+    ASSERT_THAT(
+        icing.Get("namespace", "uri2", GetResultSpecProto::default_instance())
+            .status(),
+        ProtoIsOk());
+    ASSERT_THAT(
+        icing.Get("namespace", "uri3", GetResultSpecProto::default_instance())
+            .status(),
+        ProtoIsOk());
+
+    SearchSpecProto search_spec;
+    search_spec.set_term_match_type(TermMatchType::PREFIX);
+    search_spec.set_query("message");
+    search_spec.set_search_type(GetParam());
+    SearchResultProto results =
+        icing.Search(search_spec, ScoringSpecProto::default_instance(),
+                     ResultSpecProto::default_instance());
+    ASSERT_THAT(results.results(), SizeIs(3));
+    EXPECT_THAT(results.results(0).document(), EqualsProto(document3));
+    EXPECT_THAT(results.results(1).document(), EqualsProto(document2));
+    EXPECT_THAT(results.results(2).document(), EqualsProto(document1));
+  }
+
+  // Reinitializate with document_store_namespace_id_fingerprint being false,
+  // and test that we are still able to read/query docs.
+  {
+    IcingSearchEngineOptions options = GetDefaultIcingOptions();
+    options.set_document_store_namespace_id_fingerprint(false);
+    IcingSearchEngine icing(options, GetTestJniCache());
+    ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
+
+    ASSERT_THAT(
+        icing.Get("namespace", "uri1", GetResultSpecProto::default_instance())
+            .status(),
+        ProtoIsOk());
+    ASSERT_THAT(
+        icing.Get("namespace", "uri2", GetResultSpecProto::default_instance())
+            .status(),
+        ProtoIsOk());
+    ASSERT_THAT(
+        icing.Get("namespace", "uri3", GetResultSpecProto::default_instance())
+            .status(),
+        ProtoIsOk());
+
+    SearchSpecProto search_spec;
+    search_spec.set_term_match_type(TermMatchType::PREFIX);
+    search_spec.set_query("message");
+    search_spec.set_search_type(GetParam());
+    SearchResultProto results =
+        icing.Search(search_spec, ScoringSpecProto::default_instance(),
+                     ResultSpecProto::default_instance());
+    ASSERT_THAT(results.results(), SizeIs(3));
+    EXPECT_THAT(results.results(0).document(), EqualsProto(document3));
+    EXPECT_THAT(results.results(1).document(), EqualsProto(document2));
+    EXPECT_THAT(results.results(2).document(), EqualsProto(document1));
+  }
+}
+
 INSTANTIATE_TEST_SUITE_P(
     IcingSearchEngineSearchTest, IcingSearchEngineSearchTest,
     testing::Values(
diff --git a/icing/icing-search-engine_suggest_test.cc b/icing/icing-search-engine_suggest_test.cc
index 6973ad0..b3aeafc 100644
--- a/icing/icing-search-engine_suggest_test.cc
+++ b/icing/icing-search-engine_suggest_test.cc
@@ -12,8 +12,6 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-#include "icing/icing-search-engine.h"
-
 #include <cstdint>
 #include <limits>
 #include <memory>
@@ -25,6 +23,7 @@
 #include "gtest/gtest.h"
 #include "icing/document-builder.h"
 #include "icing/file/filesystem.h"
+#include "icing/icing-search-engine.h"
 #include "icing/jni/jni-cache.h"
 #include "icing/portable/endian.h"
 #include "icing/portable/equals-proto.h"
@@ -1508,6 +1507,95 @@ TEST_F(IcingSearchEngineSuggestTest,
               UnorderedElementsAre(EqualsProto(suggestionBarCatSubjectFoo)));
 }
 
+TEST_F(IcingSearchEngineSuggestTest, SearchSuggestionsTest_InvalidPrefixTest) {
+  IcingSearchEngine icing(GetDefaultIcingOptions(), GetTestJniCache());
+  ASSERT_THAT(icing.Initialize().status(), ProtoIsOk());
+  ASSERT_THAT(icing.SetSchema(CreatePersonAndEmailSchema()).status(),
+              ProtoIsOk());
+
+  DocumentProto document1 =
+      DocumentBuilder()
+          .SetKey("namespace1", "uri1")
+          .SetSchema("Email")
+          .SetCreationTimestampMs(10)
+          .AddStringProperty("subject", "bar fo")  // "bar fo"
+          .AddStringProperty("body", "fool")
+          .Build();
+  DocumentProto document2 =
+      DocumentBuilder()
+          .SetKey("namespace1", "uri2")
+          .SetSchema("Email")
+          .SetCreationTimestampMs(10)
+          .AddStringProperty("subject", "bar cat foo")  // "bar cat fool"
+          .AddStringProperty("body", "fool")
+          .Build();
+  DocumentProto document3 = DocumentBuilder()
+                                .SetKey("namespace1", "uri3")
+                                .SetSchema("Email")
+                                .SetCreationTimestampMs(10)
+                                .AddStringProperty("subject", "fool")  // "fool"
+                                .AddStringProperty("body", "fool")
+                                .Build();
+  ASSERT_THAT(icing.Put(document1).status(), ProtoIsOk());
+  ASSERT_THAT(icing.Put(document2).status(), ProtoIsOk());
+  ASSERT_THAT(icing.Put(document3).status(), ProtoIsOk());
+
+  // Search for "f OR"
+  SuggestionSpecProto suggestion_spec;
+  suggestion_spec.set_prefix("f OR");
+  suggestion_spec.set_num_to_return(10);
+  suggestion_spec.mutable_scoring_spec()->set_scoring_match_type(
+      TermMatchType::PREFIX);
+  suggestion_spec.mutable_scoring_spec()->set_rank_by(
+      SuggestionScoringSpecProto::SuggestionRankingStrategy::DOCUMENT_COUNT);
+
+  SuggestionResponse response = icing.SearchSuggestions(suggestion_spec);
+  if (SearchSpecProto::default_instance().search_type() ==
+      SearchSpecProto::SearchType::ICING_RAW_QUERY) {
+    EXPECT_THAT(response.status(), ProtoIsOk());
+    EXPECT_THAT(response.suggestions(), IsEmpty());
+  } else {
+    EXPECT_THAT(response.status(),
+                ProtoStatusIs(StatusProto::INVALID_ARGUMENT));
+    EXPECT_THAT(response.suggestions(), IsEmpty());
+  }
+
+  // TODO(b/208654892): Update handling for hyphens to only consider it a hyphen
+  // within a TEXT token (rather than a MINUS token) when surrounded on both
+  // sides by TEXT rather than just preceded by TEXT.
+  // Search for "f-"
+  suggestion_spec.set_prefix("f-");
+  response = icing.SearchSuggestions(suggestion_spec);
+  EXPECT_THAT(response.status(), ProtoIsOk());
+  EXPECT_THAT(response.suggestions(), IsEmpty());
+
+  // Search for "f:"
+  suggestion_spec.set_prefix("f:");
+  response = icing.SearchSuggestions(suggestion_spec);
+  if (SearchSpecProto::default_instance().search_type() ==
+      SearchSpecProto::SearchType::ICING_RAW_QUERY) {
+    EXPECT_THAT(response.status(), ProtoIsOk());
+    EXPECT_THAT(response.suggestions(), IsEmpty());
+  } else {
+    EXPECT_THAT(response.status(),
+                ProtoStatusIs(StatusProto::INVALID_ARGUMENT));
+    EXPECT_THAT(response.suggestions(), IsEmpty());
+  }
+
+  // Search for "OR OR - :"
+  suggestion_spec.set_prefix("OR OR - :");
+  response = icing.SearchSuggestions(suggestion_spec);
+  if (SearchSpecProto::default_instance().search_type() ==
+      SearchSpecProto::SearchType::ICING_RAW_QUERY) {
+    EXPECT_THAT(response.status(), ProtoIsOk());
+    EXPECT_THAT(response.suggestions(), IsEmpty());
+  } else {
+    EXPECT_THAT(response.status(),
+                ProtoStatusIs(StatusProto::INVALID_ARGUMENT));
+    EXPECT_THAT(response.suggestions(), IsEmpty());
+  }
+}
+
 }  // namespace
 }  // namespace lib
 }  // namespace icing
diff --git a/icing/index/index-processor_test.cc b/icing/index/index-processor_test.cc
index 3a9b4ee..47baabe 100644
--- a/icing/index/index-processor_test.cc
+++ b/icing/index/index-processor_test.cc
@@ -40,6 +40,8 @@
 #include "icing/index/numeric/numeric-index.h"
 #include "icing/index/string-section-indexing-handler.h"
 #include "icing/index/term-property-id.h"
+#include "icing/join/qualified-id-joinable-property-indexing-handler.h"
+#include "icing/join/qualified-id-type-joinable-index.h"
 #include "icing/legacy/index/icing-filesystem.h"
 #include "icing/legacy/index/icing-mock-filesystem.h"
 #include "icing/portable/platform.h"
@@ -51,6 +53,7 @@
 #include "icing/schema/schema-util.h"
 #include "icing/schema/section.h"
 #include "icing/store/document-id.h"
+#include "icing/store/document-store.h"
 #include "icing/testing/common-matchers.h"
 #include "icing/testing/fake-clock.h"
 #include "icing/testing/icu-data-file-helper.h"
@@ -160,7 +163,9 @@ class IndexProcessorTest : public Test {
 
     index_dir_ = base_dir_ + "/index";
     integer_index_dir_ = base_dir_ + "/integer_index";
+    qualified_id_join_index_dir_ = base_dir_ + "/qualified_id_join_index";
     schema_store_dir_ = base_dir_ + "/schema_store";
+    doc_store_dir_ = base_dir_ + "/doc_store";
 
     Index::Options options(index_dir_, /*index_merge_size=*/1024 * 1024);
     ICING_ASSERT_OK_AND_ASSIGN(
@@ -169,6 +174,10 @@ class IndexProcessorTest : public Test {
     ICING_ASSERT_OK_AND_ASSIGN(
         integer_index_, IntegerIndex::Create(filesystem_, integer_index_dir_));
 
+    ICING_ASSERT_OK_AND_ASSIGN(qualified_id_join_index_,
+                               QualifiedIdTypeJoinableIndex::Create(
+                                   filesystem_, qualified_id_join_index_dir_));
+
     language_segmenter_factory::SegmenterOptions segmenter_options(ULOC_US);
     ICING_ASSERT_OK_AND_ASSIGN(
         lang_segmenter_,
@@ -260,6 +269,13 @@ class IndexProcessorTest : public Test {
             .Build();
     ICING_ASSERT_OK(schema_store_->SetSchema(schema));
 
+    ASSERT_TRUE(filesystem_.CreateDirectoryRecursively(doc_store_dir_.c_str()));
+    ICING_ASSERT_OK_AND_ASSIGN(
+        DocumentStore::CreateResult create_result,
+        DocumentStore::Create(&filesystem_, doc_store_dir_, &fake_clock_,
+                              schema_store_.get()));
+    doc_store_ = std::move(create_result.document_store);
+
     ICING_ASSERT_OK_AND_ASSIGN(
         std::unique_ptr<StringSectionIndexingHandler>
             string_section_indexing_handler,
@@ -269,9 +285,16 @@ class IndexProcessorTest : public Test {
                                    integer_section_indexing_handler,
                                IntegerSectionIndexingHandler::Create(
                                    &fake_clock_, integer_index_.get()));
+    ICING_ASSERT_OK_AND_ASSIGN(
+        std::unique_ptr<QualifiedIdJoinablePropertyIndexingHandler>
+            qualified_id_joinable_property_indexing_handler,
+        QualifiedIdJoinablePropertyIndexingHandler::Create(
+            &fake_clock_, qualified_id_join_index_.get()));
     std::vector<std::unique_ptr<DataIndexingHandler>> handlers;
     handlers.push_back(std::move(string_section_indexing_handler));
     handlers.push_back(std::move(integer_section_indexing_handler));
+    handlers.push_back(
+        std::move(qualified_id_joinable_property_indexing_handler));
 
     index_processor_ =
         std::make_unique<IndexProcessor>(std::move(handlers), &fake_clock_);
@@ -281,9 +304,11 @@ class IndexProcessorTest : public Test {
 
   void TearDown() override {
     index_processor_.reset();
+    doc_store_.reset();
     schema_store_.reset();
     normalizer_.reset();
     lang_segmenter_.reset();
+    qualified_id_join_index_.reset();
     integer_index_.reset();
     index_.reset();
 
@@ -298,13 +323,17 @@ class IndexProcessorTest : public Test {
   std::string base_dir_;
   std::string index_dir_;
   std::string integer_index_dir_;
+  std::string qualified_id_join_index_dir_;
   std::string schema_store_dir_;
+  std::string doc_store_dir_;
 
   std::unique_ptr<Index> index_;
   std::unique_ptr<NumericIndex<int64_t>> integer_index_;
+  std::unique_ptr<QualifiedIdTypeJoinableIndex> qualified_id_join_index_;
   std::unique_ptr<LanguageSegmenter> lang_segmenter_;
   std::unique_ptr<Normalizer> normalizer_;
   std::unique_ptr<SchemaStore> schema_store_;
+  std::unique_ptr<DocumentStore> doc_store_;
 
   std::unique_ptr<IndexProcessor> index_processor_;
 };
@@ -788,9 +817,16 @@ TEST_F(IndexProcessorTest, OutOfOrderDocumentIdsInRecoveryMode) {
                                  integer_section_indexing_handler,
                              IntegerSectionIndexingHandler::Create(
                                  &fake_clock_, integer_index_.get()));
+  ICING_ASSERT_OK_AND_ASSIGN(
+      std::unique_ptr<QualifiedIdJoinablePropertyIndexingHandler>
+          qualified_id_joinable_property_indexing_handler,
+      QualifiedIdJoinablePropertyIndexingHandler::Create(
+          &fake_clock_, qualified_id_join_index_.get()));
   std::vector<std::unique_ptr<DataIndexingHandler>> handlers;
   handlers.push_back(std::move(string_section_indexing_handler));
   handlers.push_back(std::move(integer_section_indexing_handler));
+  handlers.push_back(
+      std::move(qualified_id_joinable_property_indexing_handler));
 
   IndexProcessor index_processor(std::move(handlers), &fake_clock_,
                                  /*recovery_mode=*/true);
@@ -1506,10 +1542,10 @@ TEST_F(IndexProcessorTest, IndexableIntegerProperty) {
   EXPECT_THAT(index_processor_->IndexDocument(tokenized_document, kDocumentId0),
               IsOk());
 
-  ICING_ASSERT_OK_AND_ASSIGN(
-      std::unique_ptr<DocHitInfoIterator> itr,
-      integer_index_->GetIterator(kIndexableIntegerProperty, /*key_lower=*/1,
-                                  /*key_upper=*/5));
+  ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<DocHitInfoIterator> itr,
+                             integer_index_->GetIterator(
+                                 kIndexableIntegerProperty, /*key_lower=*/1,
+                                 /*key_upper=*/5, *doc_store_, *schema_store_));
 
   EXPECT_THAT(
       GetHits(std::move(itr)),
@@ -1535,10 +1571,10 @@ TEST_F(IndexProcessorTest, IndexableIntegerPropertyNoMatch) {
   EXPECT_THAT(index_processor_->IndexDocument(tokenized_document, kDocumentId0),
               IsOk());
 
-  ICING_ASSERT_OK_AND_ASSIGN(
-      std::unique_ptr<DocHitInfoIterator> itr,
-      integer_index_->GetIterator(kIndexableIntegerProperty, /*key_lower=*/-1,
-                                  /*key_upper=*/0));
+  ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<DocHitInfoIterator> itr,
+                             integer_index_->GetIterator(
+                                 kIndexableIntegerProperty, /*key_lower=*/-1,
+                                 /*key_upper=*/0, *doc_store_, *schema_store_));
 
   EXPECT_THAT(GetHits(std::move(itr)), IsEmpty());
 }
diff --git a/icing/index/iterator/doc-hit-info-iterator-not.cc b/icing/index/iterator/doc-hit-info-iterator-not.cc
index 1818f08..38b1ded 100644
--- a/icing/index/iterator/doc-hit-info-iterator-not.cc
+++ b/icing/index/iterator/doc-hit-info-iterator-not.cc
@@ -63,8 +63,8 @@ libtextclassifier3::Status DocHitInfoIteratorNot::Advance() {
 libtextclassifier3::StatusOr<DocHitInfoIterator::TrimmedNode>
 DocHitInfoIteratorNot::TrimRightMostNode() && {
   // Don't generate suggestion if the last operator is NOT.
-  return absl_ports::UnimplementedError(
-      "Cannot trim right most node in NOT operator.");
+  return absl_ports::InvalidArgumentError(
+      "Cannot generate suggestion if the last term is NOT operator.");
 }
 
 int32_t DocHitInfoIteratorNot::GetNumBlocksInspected() const {
diff --git a/icing/index/iterator/doc-hit-info-iterator-not_test.cc b/icing/index/iterator/doc-hit-info-iterator-not_test.cc
index 54d6c36..5a8ce2c 100644
--- a/icing/index/iterator/doc-hit-info-iterator-not_test.cc
+++ b/icing/index/iterator/doc-hit-info-iterator-not_test.cc
@@ -163,7 +163,7 @@ TEST(DocHitInfoIteratorNotTest, TrimNotIterator) {
   DocHitInfoIteratorNot not_iterator(std::move(to_be_excluded_iterator),
                                      /*document_id_limit=*/5);
   EXPECT_THAT(std::move(not_iterator).TrimRightMostNode(),
-              StatusIs(libtextclassifier3::StatusCode::UNIMPLEMENTED));
+              StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
 }
 
 }  // namespace
diff --git a/icing/index/numeric/doc-hit-info-iterator-numeric.h b/icing/index/numeric/doc-hit-info-iterator-numeric.h
index bf990d1..fc66a1d 100644
--- a/icing/index/numeric/doc-hit-info-iterator-numeric.h
+++ b/icing/index/numeric/doc-hit-info-iterator-numeric.h
@@ -49,8 +49,8 @@ class DocHitInfoIteratorNumeric : public DocHitInfoIterator {
   }
 
   libtextclassifier3::StatusOr<TrimmedNode> TrimRightMostNode() && override {
-    return absl_ports::UnimplementedError(
-        "Cannot trim right most node in numeric operator.");
+    return absl_ports::InvalidArgumentError(
+        "Cannot generate suggestion if the last term is numeric operator.");
   }
 
   int32_t GetNumBlocksInspected() const override { return 0; }
diff --git a/icing/index/numeric/dummy-numeric-index.h b/icing/index/numeric/dummy-numeric-index.h
index 164866c..7cfb102 100644
--- a/icing/index/numeric/dummy-numeric-index.h
+++ b/icing/index/numeric/dummy-numeric-index.h
@@ -70,7 +70,8 @@ class DummyNumericIndex : public NumericIndex<T> {
   }
 
   libtextclassifier3::StatusOr<std::unique_ptr<DocHitInfoIterator>> GetIterator(
-      std::string_view property_path, T key_lower, T key_upper) const override;
+      std::string_view property_path, T key_lower, T key_upper,
+      const DocumentStore&, const SchemaStore&) const override;
 
   libtextclassifier3::Status Optimize(
       const std::vector<DocumentId>& document_id_old_to_new,
@@ -93,6 +94,8 @@ class DummyNumericIndex : public NumericIndex<T> {
     }
   }
 
+  int num_property_indices() const override { return storage_.size(); }
+
  private:
   class Editor : public NumericIndex<T>::Editor {
    public:
@@ -176,7 +179,6 @@ class DummyNumericIndex : public NumericIndex<T> {
     DocHitInfo doc_hit_info_;
   };
 
- private:
   explicit DummyNumericIndex(const Filesystem& filesystem,
                              std::string&& working_path)
       : NumericIndex<T>(filesystem, std::move(working_path),
@@ -265,7 +267,8 @@ libtextclassifier3::Status DummyNumericIndex<T>::Iterator::Advance() {
 template <typename T>
 libtextclassifier3::StatusOr<std::unique_ptr<DocHitInfoIterator>>
 DummyNumericIndex<T>::GetIterator(std::string_view property_path, T key_lower,
-                                  T key_upper) const {
+                                  T key_upper, const DocumentStore&,
+                                  const SchemaStore&) const {
   if (key_lower > key_upper) {
     return absl_ports::InvalidArgumentError(
         "key_lower should not be greater than key_upper");
diff --git a/icing/index/numeric/integer-index-bucket-util.cc b/icing/index/numeric/integer-index-bucket-util.cc
new file mode 100644
index 0000000..a05baab
--- /dev/null
+++ b/icing/index/numeric/integer-index-bucket-util.cc
@@ -0,0 +1,205 @@
+// Copyright (C) 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "icing/index/numeric/integer-index-bucket-util.h"
+
+#include <algorithm>
+#include <cstdint>
+#include <iterator>
+#include <limits>
+#include <utility>
+#include <vector>
+
+#include "icing/index/numeric/integer-index-data.h"
+
+namespace icing {
+namespace lib {
+
+namespace integer_index_bucket_util {
+
+namespace {
+
+// Helper function to determine if data slice [start, end) forms a "full
+// single-range bucket".
+//
+// Full single-range bucket: keys of all data are identical and # of them exceed
+// num_data_threshold.
+//
+// REQUIRES: data slice [start, end) are sorted by key.
+inline bool WouldBeFullSingleRangeBucket(
+    const std::vector<IntegerIndexData>::iterator& start,
+    const std::vector<IntegerIndexData>::iterator& end,
+    int32_t num_data_threshold) {
+  return std::distance(start, end) > num_data_threshold &&
+         start->key() == (end - 1)->key();
+}
+
+// Helper function to determine if a bucket is full single-range.
+//
+// REQUIRES:
+//   bucket.key_lower <= [bucket.start, bucket.end)->key() <= bucket.key_upper
+inline bool IsFullSingleRangeBucket(const DataRangeAndBucketInfo& bucket,
+                                    int32_t num_data_threshold) {
+  return bucket.key_lower == bucket.key_upper &&
+         WouldBeFullSingleRangeBucket(bucket.start, bucket.end,
+                                      num_data_threshold);
+}
+
+// Helper function to append new bucket(s) with corresponding data slice for
+// range [curr_key_lower, last_key] where last_key = (it_end - 1)->key().
+//
+// Also it handles an edge case:
+// If data slice [it_start, it_end) forms a "full single-range bucket" (see
+// WouldBeFullSingleRangeBucket for definition), then we have to put them into a
+// single range bucket [last_key, last_key] instead of [curr_key_lower,
+// last_key]. Also we have to deal with range [curr_key_lower, last_key - 1]:
+// - If the previous bucket exists and it is not a "full single-range bucket",
+//   then merge [curr_key_lower, last_key - 1] into the previous bucket, i.e.
+//   change the previous bucket's key_upper to (last_key - 1). Then we will end
+//   up having:
+//   - [prev_bucket.key_lower, last_key - 1]
+//   - [last_key, last_key]
+// - Otherwise, we have to create [curr_key_lower, last_key - 1] with
+//   empty data. Then we will end up having (Note: prev_bucket.key_upper ==
+//   curr_key_lower - 1):
+//   - [prev_bucket.key_lower, curr_key_lower - 1]
+//   - [curr_key_lower, last_key - 1]
+//   - [last_key, last_key]
+// This will avoid split bucket being called too frequently.
+// For example, original_key_lower = 0, original_key_upper = 50. If we have
+// (num_data_threshold + 1) data with key = 20 and another data with key = 40:
+// - Without this part, we will split them into [[0, 20], [21, 50]]. Then when
+//   adding data with key = 10 next round, we will invoke split again and split
+//   [0, 20] to [[0, 10], [11, 20]].
+// - With this part, we will split them into [[0, 19], [20, 20], [21, 50]],
+//   which will avoid splitting in the next round for key = 20.
+//
+// REQUIRES: it_start < it_end
+void AppendNewBuckets(const std::vector<IntegerIndexData>::iterator& it_start,
+                      const std::vector<IntegerIndexData>::iterator& it_end,
+                      int64_t curr_key_lower, int32_t num_data_threshold,
+                      std::vector<DataRangeAndBucketInfo>& results) {
+  int64_t last_key = (it_end - 1)->key();
+  if (curr_key_lower < last_key &&
+      WouldBeFullSingleRangeBucket(it_start, it_end, num_data_threshold)) {
+    if (!results.empty() &&
+        !IsFullSingleRangeBucket(results.back(), num_data_threshold)) {
+      // Previous bucket is not full single-range, so merge it to now hold the
+      // range [prev_bucket.key_lower, last_key - 1].
+      results.back().key_upper = last_key - 1;
+    } else {
+      // There is either no previous bucket or the previous bucket is full
+      // single-range. So add an empty bucket for the range [curr_key_lower,
+      // last_key - 1].
+      results.push_back(DataRangeAndBucketInfo(it_start, it_start,
+                                               curr_key_lower, last_key - 1));
+    }
+    curr_key_lower = last_key;
+  }
+  results.push_back(
+      DataRangeAndBucketInfo(it_start, it_end, curr_key_lower, last_key));
+}
+
+}  // namespace
+
+std::vector<DataRangeAndBucketInfo> Split(std::vector<IntegerIndexData>& data,
+                                          int64_t original_key_lower,
+                                          int64_t original_key_upper,
+                                          int32_t num_data_threshold) {
+  // Early return if there is no need to split.
+  if (data.size() <= num_data_threshold) {
+    return {DataRangeAndBucketInfo(data.begin(), data.end(), original_key_lower,
+                                   original_key_upper)};
+  }
+
+  // Sort data by key.
+  std::sort(
+      data.begin(), data.end(),
+      [](const IntegerIndexData& lhs, const IntegerIndexData& rhs) -> bool {
+        return lhs.key() < rhs.key();
+      });
+
+  std::vector<DataRangeAndBucketInfo> results;
+  int64_t curr_key_lower = original_key_lower;
+  // Sliding window [it_start, it_end) to separate data into different buckets.
+  auto it_start = data.begin();
+  auto it_end = data.begin();
+  while (it_end != data.end()) {
+    // Attempt to extend it_end by 1, but we have to include all data with the
+    // same key since they cannot be separated into different buckets. Also use
+    // extend_it_end to avoid modifying it_end directly. For some edge cases,
+    // the extension in a single round is extremely large (i.e. a lot of data
+    // have the same key), and we want to separate them. For example:
+    // - key = 0: 5 data
+    // - key = 1: num_data_threshold - 1 data
+    // In the second round, # of data in the sliding window will exceed the
+    // threshold. We want to separate all data with key = 0 into a single bucket
+    // instead of putting key = 0 and key = 1 together. Therefore, using
+    // extend_it_end allow us to preserve it_end of the previous round and be
+    // able to deal with this case.
+    auto extend_it_end = it_end + 1;
+    while (extend_it_end != data.end() &&
+           it_end->key() == extend_it_end->key()) {
+      ++extend_it_end;
+    }
+
+    if (std::distance(it_start, extend_it_end) > num_data_threshold &&
+        it_start != it_end) {
+      // Split data between [it_start, it_end) into range [curr_key_lower,
+      // (it_end - 1)->key()].
+      AppendNewBuckets(it_start, it_end, curr_key_lower, num_data_threshold,
+                       results);
+
+      // it_end at this moment won't be data.end(), so the last element of the
+      // new bucket can't have key == INT64_MAX. Therefore, it is safe to set
+      // curr_key_lower as ((it_end - 1)->key() + 1).
+      curr_key_lower = (it_end - 1)->key() + 1;
+      it_start = it_end;
+    }
+    it_end = extend_it_end;
+  }
+
+  // Handle the final range [curr_key_lower, original_key_upper].
+  if (curr_key_lower <= original_key_upper) {
+    if (it_start != it_end) {
+      AppendNewBuckets(it_start, it_end, curr_key_lower, num_data_threshold,
+                       results);
+
+      // AppendNewBuckets only handles range [curr_key_lower, (it_end -
+      // 1)->key()], so we have to handle range [(it_end - 1)->key() + 1,
+      // original_key_upper] if needed.
+      int64_t last_key = (it_end - 1)->key();
+      if (last_key != std::numeric_limits<int64_t>::max() &&
+          last_key + 1 <= original_key_upper) {
+        if (!results.empty() &&
+            !IsFullSingleRangeBucket(results.back(), num_data_threshold)) {
+          results.back().key_upper = original_key_upper;
+        } else {
+          results.push_back(DataRangeAndBucketInfo(
+              it_start, it_start, last_key + 1, original_key_upper));
+        }
+      }
+    } else {
+      results.push_back(DataRangeAndBucketInfo(it_start, it_end, curr_key_lower,
+                                               original_key_upper));
+    }
+  }
+
+  return results;
+}
+
+}  // namespace integer_index_bucket_util
+
+}  // namespace lib
+}  // namespace icing
diff --git a/icing/index/numeric/integer-index-bucket-util.h b/icing/index/numeric/integer-index-bucket-util.h
new file mode 100644
index 0000000..863bd01
--- /dev/null
+++ b/icing/index/numeric/integer-index-bucket-util.h
@@ -0,0 +1,81 @@
+// Copyright (C) 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ICING_INDEX_NUMERIC_INTEGER_INDEX_BUCKET_UTIL_H_
+#define ICING_INDEX_NUMERIC_INTEGER_INDEX_BUCKET_UTIL_H_
+
+#include <cstdint>
+#include <utility>
+#include <vector>
+
+#include "icing/index/numeric/integer-index-data.h"
+
+namespace icing {
+namespace lib {
+
+namespace integer_index_bucket_util {
+
+// A wrapper struct that contains information of a bucket.
+// - The bucket contains data within the iterator [start, end).
+// - Bucket range is [key_lower, key_upper], and all data within [start, end)
+//   should have keys in the bucket range.
+//
+// Note: the caller should make sure the lifecycle of data vector is longer than
+// instances of this wrapper struct.
+struct DataRangeAndBucketInfo {
+  std::vector<IntegerIndexData>::iterator start;
+  std::vector<IntegerIndexData>::iterator end;
+  int64_t key_lower;
+  int64_t key_upper;
+
+  explicit DataRangeAndBucketInfo(
+      std::vector<IntegerIndexData>::iterator start_in,
+      std::vector<IntegerIndexData>::iterator end_in, int64_t key_lower_in,
+      int64_t key_upper_in)
+      : start(std::move(start_in)),
+        end(std::move(end_in)),
+        key_lower(key_lower_in),
+        key_upper(key_upper_in) {}
+};
+
+// Helper function to split data (that are originally in a bucket with range
+// [original_key_lower, original_key_upper]) into different buckets according to
+// num_data_threshold.
+// - The input vector `data` will be sorted by key in ascending order (unless
+//   there's no need to split in which case data is returned unmodified)
+// - Data with the same key will be in the same bucket even if # of them exceed
+//   num_data_threshold.
+// - Range of all buckets will be disjoint, and the range union will be
+//   [original_key_lower, original_key_upper].
+// - Data slice (i.e. [start, end)) can be empty.
+//
+// REQUIRES:
+// - original_key_lower <= original_key_upper
+// - num_data_threshold > 0
+// - Keys of all data are in range [original_key_lower, original_key_upper]
+//
+// Returns: a vector of DataRangeAndBucketInfo that contain all bucket info
+//   after splitting. Also the returned vector should contain at least one
+//   bucket, otherwise it is considered an error.
+std::vector<DataRangeAndBucketInfo> Split(std::vector<IntegerIndexData>& data,
+                                          int64_t original_key_lower,
+                                          int64_t original_key_upper,
+                                          int32_t num_data_threshold);
+
+}  // namespace integer_index_bucket_util
+
+}  // namespace lib
+}  // namespace icing
+
+#endif  // ICING_INDEX_NUMERIC_INTEGER_INDEX_BUCKET_UTIL_H_
diff --git a/icing/index/numeric/integer-index-bucket-util_test.cc b/icing/index/numeric/integer-index-bucket-util_test.cc
new file mode 100644
index 0000000..82c593e
--- /dev/null
+++ b/icing/index/numeric/integer-index-bucket-util_test.cc
@@ -0,0 +1,1112 @@
+// Copyright (C) 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "icing/index/numeric/integer-index-bucket-util.h"
+
+#include <limits>
+#include <vector>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include "icing/index/numeric/integer-index-data.h"
+#include "icing/schema/section.h"
+#include "icing/store/document-id.h"
+
+namespace icing {
+namespace lib {
+namespace integer_index_bucket_util {
+
+namespace {
+
+using ::testing::ElementsAre;
+using ::testing::Eq;
+using ::testing::IsEmpty;
+using ::testing::Ne;
+using ::testing::SizeIs;
+
+static constexpr DocumentId kDefaultDocumentId = 123;
+static constexpr SectionId kDefaultSectionId = 31;
+
+TEST(IntegerIndexBucketUtilTest, Split_numDataNotDivisibleByThreshold) {
+  std::vector<IntegerIndexData> data = {
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -3),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 0),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 1),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -2)};
+  int64_t key_lower = -10;
+  int64_t key_upper = 10;
+  int32_t num_data_threshold = 3;
+  ASSERT_THAT(data.size() % num_data_threshold, Ne(0));
+
+  // Keys = [-10, -3, -2, 0, 1, 2, 10].
+  std::vector<DataRangeAndBucketInfo> results =
+      Split(data, key_lower, key_upper, num_data_threshold);
+  ASSERT_THAT(results, SizeIs(3));
+  // Bucket 0: key lower = -10, key upper = -2, keys = [-10, -3, -2].
+  EXPECT_THAT(results[0].key_lower, Eq(-10));
+  EXPECT_THAT(results[0].key_upper, Eq(-2));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[0].start, results[0].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -3),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -2)));
+  // Bucket 1: key lower = -1, key upper = 2, keys = [0, 1, 2].
+  EXPECT_THAT(results[1].key_lower, Eq(-1));
+  EXPECT_THAT(results[1].key_upper, Eq(2));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[1].start, results[1].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 0),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 1),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2)));
+  // Bucket 2: key lower = 3, key upper = 10, keys = [10].
+  EXPECT_THAT(results[2].key_lower, Eq(3));
+  EXPECT_THAT(results[2].key_upper, Eq(10));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[2].start, results[2].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10)));
+}
+
+TEST(IntegerIndexBucketUtilTest, Split_numDataDivisibleByThreshold) {
+  std::vector<IntegerIndexData> data = {
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -3),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 0),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -2)};
+  int64_t key_lower = -10;
+  int64_t key_upper = 10;
+  int32_t num_data_threshold = 3;
+  ASSERT_THAT(data.size() % num_data_threshold, Eq(0));
+
+  // Keys = [-10, -3, -2, 0, 2, 10].
+  std::vector<DataRangeAndBucketInfo> results =
+      Split(data, key_lower, key_upper, num_data_threshold);
+  ASSERT_THAT(results, SizeIs(2));
+  // Bucket 0: key lower = -10, key upper = -2, keys = [-10, -3, -2].
+  EXPECT_THAT(results[0].key_lower, Eq(-10));
+  EXPECT_THAT(results[0].key_upper, Eq(-2));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[0].start, results[0].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -3),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -2)));
+  // Bucket 1: key lower = -1, key upper = 2, keys = [0, 2, 10].
+  EXPECT_THAT(results[1].key_lower, Eq(-1));
+  EXPECT_THAT(results[1].key_upper, Eq(10));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[1].start, results[1].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 0),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10)));
+}
+
+TEST(IntegerIndexBucketUtilTest, Split_shouldIncludeOriginalKeyRange) {
+  std::vector<IntegerIndexData> data = {
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -3),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 0),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 1),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -2)};
+  int64_t key_lower = -1000;
+  int64_t key_upper = 1000;
+  int32_t num_data_threshold = 3;
+
+  // Keys = [-10, -3, -2, 0, 1, 2, 10].
+  // Split should include the original key_lower and key_upper even if there is
+  // no key at boundary.
+  std::vector<DataRangeAndBucketInfo> results =
+      Split(data, key_lower, key_upper, num_data_threshold);
+  ASSERT_THAT(results, SizeIs(3));
+  // Bucket 0: key lower = -1000, key upper = -2, keys = [-10, -3, -2].
+  EXPECT_THAT(results[0].key_lower, Eq(-1000));
+  EXPECT_THAT(results[0].key_upper, Eq(-2));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[0].start, results[0].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -3),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -2)));
+  // Bucket 1: key lower = -1, key upper = 2, keys = [0, 1, 2].
+  EXPECT_THAT(results[1].key_lower, Eq(-1));
+  EXPECT_THAT(results[1].key_upper, Eq(2));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[1].start, results[1].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 0),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 1),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2)));
+  // Bucket 2: key lower = 3, key upper = 1000, keys = [10].
+  EXPECT_THAT(results[2].key_lower, Eq(3));
+  EXPECT_THAT(results[2].key_upper, Eq(1000));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[2].start, results[2].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10)));
+}
+
+TEST(IntegerIndexBucketUtilTest, Split_singleBucketWithoutSplitting) {
+  std::vector<IntegerIndexData> data = {
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -3),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 0),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 1),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -2)};
+  int64_t key_lower = -1000;
+  int64_t key_upper = 1000;
+  int32_t num_data_threshold = 100;
+
+  // Keys = [-10, -3, -2, 0, 1, 2, 10].
+  std::vector<DataRangeAndBucketInfo> results =
+      Split(data, key_lower, key_upper, num_data_threshold);
+  ASSERT_THAT(results, SizeIs(1));
+  // Bucket 0: key lower = -1000, key upper = 1000, keys = [-10, -3, -2, 0, 1,
+  // 2, 10]. Since # of data <= threshold, data vector won't be sorted and thus
+  // [start, end) will have data with the original order.
+  EXPECT_THAT(results[0].key_lower, Eq(-1000));
+  EXPECT_THAT(results[0].key_upper, Eq(1000));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[0].start, results[0].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -3),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 0),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 1),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -2)));
+}
+
+TEST(IntegerIndexBucketUtilTest, Split_emptyData) {
+  std::vector<IntegerIndexData> empty_data;
+  std::vector<DataRangeAndBucketInfo> results =
+      Split(empty_data, /*original_key_lower=*/-10, /*original_key_upper=*/10,
+            /*num_data_threshold=*/3);
+  ASSERT_THAT(results, SizeIs(1));
+  // Bucket 0: key lower = -10, key upper = 10, keys = [].
+  EXPECT_THAT(results[0].key_lower, Eq(-10));
+  EXPECT_THAT(results[0].key_upper, Eq(10));
+  EXPECT_THAT(std::vector<IntegerIndexData>(results[0].start, results[0].end),
+              IsEmpty());
+}
+
+TEST(IntegerIndexBucketUtilTest,
+     Split_sameKeysExceedingThreshold_firstBucket_keyEqualsKeyLower) {
+  std::vector<IntegerIndexData> data = {
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 0),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 3),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 5),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10)};
+
+  // Keys = [-10, -10, -10, -10, -10, 0, 3, 5, 10].
+  std::vector<DataRangeAndBucketInfo> results =
+      Split(data, /*original_key_lower=*/-10, /*original_key_upper=*/10,
+            /*num_data_threshold=*/3);
+  // - Even though # of data with key = -10 exceeds the threshold, they should
+  //   still be in the same bucket.
+  // - They should be separated from key = 0, 3, ....
+  ASSERT_THAT(results, SizeIs(3));
+  // Bucket 0: key lower = -10, key upper = -10, keys = [-10, -10, -10, -10,
+  // -10].
+  EXPECT_THAT(results[0].key_lower, Eq(-10));
+  EXPECT_THAT(results[0].key_upper, Eq(-10));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[0].start, results[0].end),
+      ElementsAre(
+          IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+          IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+          IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+          IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+          IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10)));
+  // Bucket 1: key lower = -9, key upper = 5, keys = [0, 3, 5].
+  EXPECT_THAT(results[1].key_lower, Eq(-9));
+  EXPECT_THAT(results[1].key_upper, Eq(5));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[1].start, results[1].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 0),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 3),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 5)));
+  // Bucket 2: key lower = 6, key upper = 10, keys = [10].
+  EXPECT_THAT(results[2].key_lower, Eq(6));
+  EXPECT_THAT(results[2].key_upper, Eq(10));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[2].start, results[2].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10)));
+}
+
+TEST(IntegerIndexBucketUtilTest,
+     Split_sameKeysExceedingThreshold_firstBucket_keyGreaterThanKeyLower) {
+  std::vector<IntegerIndexData> data = {
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -7),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -7),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -7),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -7),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -7),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 0),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 3),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 5),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10)};
+
+  // Keys = [-7, -7, -7, -7, -7, 0, 3, 5, 10].
+  std::vector<DataRangeAndBucketInfo> results =
+      Split(data, /*original_key_lower=*/-10, /*original_key_upper=*/10,
+            /*num_data_threshold=*/3);
+  // - Even though # of data with key = -7 exceeds the threshold, they should
+  //   still be in the same bucket.
+  // - They should be separated from key = 0, 3, ....
+  // - They should be in a single range bucket [-7, -7], and another bucket
+  //   [-10, -8] with empty data should be created before it.
+  ASSERT_THAT(results, SizeIs(4));
+  // Bucket 0: key lower = -10, key upper = -8, keys = [].
+  EXPECT_THAT(results[0].key_lower, Eq(-10));
+  EXPECT_THAT(results[0].key_upper, Eq(-8));
+  EXPECT_THAT(std::vector<IntegerIndexData>(results[0].start, results[0].end),
+              IsEmpty());
+  // Bucket 1: key lower = -7, key upper = -7, keys = [-7, -7, -7, -7, -7].
+  EXPECT_THAT(results[1].key_lower, Eq(-7));
+  EXPECT_THAT(results[1].key_upper, Eq(-7));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[1].start, results[1].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -7),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -7),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -7),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -7),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -7)));
+  // Bucket 2: key lower = -6, key upper = 5, keys = [0, 3, 5].
+  EXPECT_THAT(results[2].key_lower, Eq(-6));
+  EXPECT_THAT(results[2].key_upper, Eq(5));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[2].start, results[2].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 0),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 3),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 5)));
+  // Bucket 3: key lower = 6, key upper = 10, keys = [10].
+  EXPECT_THAT(results[3].key_lower, Eq(6));
+  EXPECT_THAT(results[3].key_upper, Eq(10));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[3].start, results[3].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10)));
+}
+
+TEST(IntegerIndexBucketUtilTest,
+     Split_sameKeysExceedingThreshold_midBucket_keyEqualsKeyLower) {
+  std::vector<IntegerIndexData> data = {
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -5),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -4),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -4),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -4),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -4),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -4),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 5),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10)};
+
+  // Keys = [-10, -5, -4, -4, -4, -4, -4, 5, 10].
+  std::vector<DataRangeAndBucketInfo> results =
+      Split(data, /*original_key_lower=*/-10, /*original_key_upper=*/10,
+            /*num_data_threshold=*/3);
+  // - Even though # of data with key = -4 exceeds the threshold, they should
+  //   still be in the same bucket.
+  // - They should be separated from key = -10, -5, 5, 10.
+  ASSERT_THAT(results, SizeIs(3));
+  // Bucket 0: key lower = -10, key upper = -5, keys = [-10, -5].
+  EXPECT_THAT(results[0].key_lower, Eq(-10));
+  EXPECT_THAT(results[0].key_upper, Eq(-5));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[0].start, results[0].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -5)));
+  // Bucket 1: key lower = -4, key upper = -4, keys = [-4, -4, -4, -4, -4].
+  EXPECT_THAT(results[1].key_lower, Eq(-4));
+  EXPECT_THAT(results[1].key_upper, Eq(-4));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[1].start, results[1].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -4),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -4),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -4),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -4),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -4)));
+  // Bucket 2: key lower = -3, key upper = 10, keys = [5, 10].
+  EXPECT_THAT(results[2].key_lower, Eq(-3));
+  EXPECT_THAT(results[2].key_upper, Eq(10));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[2].start, results[2].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 5),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10)));
+}
+
+TEST(IntegerIndexBucketUtilTest,
+     Split_sameKeysExceedingThreshold_midBucket_keyGreaterThanKeyLower) {
+  std::vector<IntegerIndexData> data = {
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -5),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -1),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -1),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -1),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -1),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -1),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 5),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10)};
+
+  // Keys = [-10, -5, -1, -1, -1, -1, -1, 5, 10].
+  std::vector<DataRangeAndBucketInfo> results =
+      Split(data, /*original_key_lower=*/-10, /*original_key_upper=*/10,
+            /*num_data_threshold=*/3);
+  // - Even though # of data with key = -1 exceeds the threshold, they should
+  //   still be in the same bucket.
+  // - They should be separated from key = -10, -5, 5, 10.
+  // - They should be in a single range bucket [-1, -1], and range [-4, -2]
+  //   should be merged into the previous bucket.
+  ASSERT_THAT(results, SizeIs(3));
+  // Bucket 0: key lower = -10, key upper = -2, keys = [-10, -5].
+  EXPECT_THAT(results[0].key_lower, Eq(-10));
+  EXPECT_THAT(results[0].key_upper, Eq(-2));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[0].start, results[0].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -5)));
+  // Bucket 1: key lower = -1, key upper = -1, keys = [-1, -1, -1, -1, -1].
+  EXPECT_THAT(results[1].key_lower, Eq(-1));
+  EXPECT_THAT(results[1].key_upper, Eq(-1));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[1].start, results[1].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -1),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -1),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -1),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -1),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -1)));
+  // Bucket 2: key lower = 0, key upper = 10, keys = [5, 10].
+  EXPECT_THAT(results[2].key_lower, Eq(0));
+  EXPECT_THAT(results[2].key_upper, Eq(10));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[2].start, results[2].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 5),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10)));
+}
+
+TEST(IntegerIndexBucketUtilTest,
+     Split_sameKeysExceedingThreshold_lastBucket_keyEqualsKeyLower) {
+  std::vector<IntegerIndexData> data = {
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -3),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 0),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 3),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 3),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 3),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 3),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 3)};
+
+  // Keys = [-10, -3, 0, 2, 3, 3, 3, 3, 3].
+  std::vector<DataRangeAndBucketInfo> results =
+      Split(data, /*original_key_lower=*/-10, /*original_key_upper=*/10,
+            /*num_data_threshold=*/3);
+  // - Even though # of data with key = 3 exceeds the threshold, they should
+  //   still be in the same bucket.
+  // - They should be separated from key = -10, -3, 0, 2.
+  // - They should be in a single range bucket [3, 3], and another bucket
+  //   [4, 10] with empty data should be created after it.
+  ASSERT_THAT(results, SizeIs(4));
+  // Bucket 0: key lower = -10, key upper = 0, keys = [-10, -3, 0].
+  EXPECT_THAT(results[0].key_lower, Eq(-10));
+  EXPECT_THAT(results[0].key_upper, Eq(0));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[0].start, results[0].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -3),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 0)));
+  // Bucket 1: key lower = 1, key upper = 2, keys = [2].
+  EXPECT_THAT(results[1].key_lower, Eq(1));
+  EXPECT_THAT(results[1].key_upper, Eq(2));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[1].start, results[1].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2)));
+  // Bucket 2: key lower = 3, key upper = 10, keys = [3, 3, 3, 3, 3].
+  EXPECT_THAT(results[2].key_lower, Eq(3));
+  EXPECT_THAT(results[2].key_upper, Eq(3));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[2].start, results[2].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 3),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 3),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 3),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 3),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 3)));
+  // Bucket 3: key lower = 4, key upper = 10, keys = [].
+  EXPECT_THAT(results[3].key_lower, Eq(4));
+  EXPECT_THAT(results[3].key_upper, Eq(10));
+  EXPECT_THAT(std::vector<IntegerIndexData>(results[3].start, results[3].end),
+              IsEmpty());
+}
+
+TEST(IntegerIndexBucketUtilTest,
+     Split_sameKeysExceedingThreshold_lastBucket_keyWithinKeyLowerAndUpper) {
+  std::vector<IntegerIndexData> data = {
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -3),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 0),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 6),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 6),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 6),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 6),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 6)};
+
+  // Keys = [-10, -3, 0, 2, 6, 6, 6, 6, 6].
+  std::vector<DataRangeAndBucketInfo> results =
+      Split(data, /*original_key_lower=*/-10, /*original_key_upper=*/10,
+            /*num_data_threshold=*/3);
+  // - Even though # of data with key = 6 exceeds the threshold, they should
+  //   still be in the same bucket.
+  // - They should be separated from key = -10, -3, 0, 2.
+  // - They should be in a single range bucket [6, 6]. Range [3, 5] should be
+  //   merged into the previous bucket. and another bucket [7, 10] with empty
+  //   data should be created after it.
+  ASSERT_THAT(results, SizeIs(4));
+  // Bucket 0: key lower = -10, key upper = 0, keys = [-10, -3, 0].
+  EXPECT_THAT(results[0].key_lower, Eq(-10));
+  EXPECT_THAT(results[0].key_upper, Eq(0));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[0].start, results[0].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -3),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 0)));
+  // Bucket 1: key lower = 1, key upper = 5, keys = [2].
+  EXPECT_THAT(results[1].key_lower, Eq(1));
+  EXPECT_THAT(results[1].key_upper, Eq(5));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[1].start, results[1].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2)));
+  // Bucket 2: key lower = 6, key upper = 6, keys = [6, 6, 6, 6, 6].
+  EXPECT_THAT(results[2].key_lower, Eq(6));
+  EXPECT_THAT(results[2].key_upper, Eq(6));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[2].start, results[2].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 6),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 6),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 6),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 6),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 6)));
+  // Bucket 3: key lower = 7, key upper = 10, keys = [].
+  EXPECT_THAT(results[3].key_lower, Eq(7));
+  EXPECT_THAT(results[3].key_upper, Eq(10));
+  EXPECT_THAT(std::vector<IntegerIndexData>(results[3].start, results[3].end),
+              IsEmpty());
+}
+
+TEST(IntegerIndexBucketUtilTest,
+     Split_sameKeysExceedingThreshold_lastBucket_keyEqualsKeyUpper) {
+  std::vector<IntegerIndexData> data = {
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -3),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 0),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10)};
+
+  // Keys = [-10, -3, 0, 2, 10, 10, 10, 10, 10].
+  std::vector<DataRangeAndBucketInfo> results =
+      Split(data, /*original_key_lower=*/-10, /*original_key_upper=*/10,
+            /*num_data_threshold=*/3);
+  // - Even though # of data with key = 10 exceeds the threshold, they should
+  //   still be in the same bucket.
+  // - They should be separated from key = -10, -3, 0, 2.
+  // - They should be in a single range bucket [10, 10], and range [3, 9] should
+  //   be merged into the previous bucket.
+  ASSERT_THAT(results, SizeIs(3));
+  // Bucket 0: key lower = -10, key upper = 0, keys = [-10, -3, 0].
+  EXPECT_THAT(results[0].key_lower, Eq(-10));
+  EXPECT_THAT(results[0].key_upper, Eq(0));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[0].start, results[0].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -3),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 0)));
+  // Bucket 1: key lower = 1, key upper = 9, keys = [2].
+  EXPECT_THAT(results[1].key_lower, Eq(1));
+  EXPECT_THAT(results[1].key_upper, Eq(9));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[1].start, results[1].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2)));
+  // Bucket 2: key lower = 10, key upper = 10, keys = [10, 10, 10, 10, 10].
+  EXPECT_THAT(results[2].key_lower, Eq(10));
+  EXPECT_THAT(results[2].key_upper, Eq(10));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[2].start, results[2].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10)));
+}
+
+TEST(IntegerIndexBucketUtilTest,
+     Split_sameKeysExceedingThreshold_shouldNotMergeIntoPreviousBucket) {
+  std::vector<IntegerIndexData> data = {
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -2),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -2),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -2),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -2),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -2),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 5),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 5),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 5),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 5),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 5),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10)};
+
+  // Keys = [-10, -2, -2, -2, -2, -2, 5, 5, 5, 5, 5, 10].
+  std::vector<DataRangeAndBucketInfo> results =
+      Split(data, /*original_key_lower=*/-10, /*original_key_upper=*/10,
+            /*num_data_threshold=*/3);
+  // - Data with key = -2 and 5 should be put into a single bucket respectively.
+  // - When dealing with key = 5, range [-1, 4] should not be merged into the
+  //   previous bucket [-2, -2] because [-2, -2] also contains single key data
+  //   exceeding the threshold. Instead, we should create bucket [-1, 4] with
+  //   empty data.
+  ASSERT_THAT(results, SizeIs(5));
+  // Bucket 0: key lower = -10, key upper = -3, keys = [-10].
+  EXPECT_THAT(results[0].key_lower, Eq(-10));
+  EXPECT_THAT(results[0].key_upper, Eq(-3));
+  EXPECT_THAT(std::vector<IntegerIndexData>(results[0].start, results[0].end),
+              ElementsAre(IntegerIndexData(kDefaultSectionId,
+                                           kDefaultDocumentId, -10)));
+  // Bucket 1: key lower = -2, key upper = -2, keys = [-2, -2, -2, -2, -2].
+  EXPECT_THAT(results[1].key_lower, Eq(-2));
+  EXPECT_THAT(results[1].key_upper, Eq(-2));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[1].start, results[1].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -2),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -2),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -2),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -2),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -2)));
+  // Bucket 2: key lower = -1, key upper = 4, keys = [].
+  EXPECT_THAT(results[2].key_lower, Eq(-1));
+  EXPECT_THAT(results[2].key_upper, Eq(4));
+  EXPECT_THAT(std::vector<IntegerIndexData>(results[2].start, results[2].end),
+              IsEmpty());
+  // Bucket 3: key lower = 5, key upper = 5, keys = [5, 5, 5, 5, 5].
+  EXPECT_THAT(results[3].key_lower, Eq(5));
+  EXPECT_THAT(results[3].key_upper, Eq(5));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[3].start, results[3].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 5),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 5),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 5),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 5),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 5)));
+  // Bucket 4: key lower = 6, key upper = 10, keys = [10].
+  EXPECT_THAT(results[4].key_lower, Eq(6));
+  EXPECT_THAT(results[4].key_upper, Eq(10));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[4].start, results[4].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10)));
+}
+
+TEST(IntegerIndexBucketUtilTest,
+     Split_sameKeysExceedingThreshold_shouldMergeIntoPreviousBucket) {
+  std::vector<IntegerIndexData> data = {
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -8),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -3),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -2),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -2),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -2),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 5),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 5),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 5),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 5),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 5),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10)};
+
+  // Keys = [-10, -8, -3, -2, -2, -2, 5, 5, 5, 5, 5, 10].
+  std::vector<DataRangeAndBucketInfo> results =
+      Split(data, /*original_key_lower=*/-10, /*original_key_upper=*/10,
+            /*num_data_threshold=*/3);
+  // - Data with key = 5 should be put into a single bucket.
+  // - When dealing with key = 5, range [-1, 4] should be merged into the
+  //   previous bucket [-2, -2] because # of data in [-2, -2] doesn't exceed the
+  //   threshold.
+  ASSERT_THAT(results, SizeIs(4));
+  // Bucket 0: key lower = -10, key upper = -3, keys = [-10, -8, -3].
+  EXPECT_THAT(results[0].key_lower, Eq(-10));
+  EXPECT_THAT(results[0].key_upper, Eq(-3));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[0].start, results[0].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -8),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -3)));
+  // Bucket 1: key lower = -2, key upper = 4, keys = [-2, -2, -2].
+  EXPECT_THAT(results[1].key_lower, Eq(-2));
+  EXPECT_THAT(results[1].key_upper, Eq(4));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[1].start, results[1].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -2),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -2),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -2)));
+  // Bucket 2: key lower = 5, key upper = 5, keys = [5, 5, 5, 5, 5].
+  EXPECT_THAT(results[2].key_lower, Eq(5));
+  EXPECT_THAT(results[2].key_upper, Eq(5));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[2].start, results[2].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 5),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 5),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 5),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 5),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 5)));
+  // Bucket 3: key lower = 6, key upper = 10, keys = [10].
+  EXPECT_THAT(results[3].key_lower, Eq(6));
+  EXPECT_THAT(results[3].key_upper, Eq(10));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[3].start, results[3].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10)));
+}
+
+TEST(IntegerIndexBucketUtilTest,
+     Split_sameKeysExceedingThreshold_singleBucket_keyEqualsKeyLower) {
+  std::vector<IntegerIndexData> data = {
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10)};
+
+  // Keys = [-10, -10, -10, -10, -10].
+  std::vector<DataRangeAndBucketInfo> results =
+      Split(data, /*original_key_lower=*/-10, /*original_key_upper=*/10,
+            /*num_data_threshold=*/3);
+  // - Even though # of data with key = -10 exceeds the threshold, they should
+  //   still be in the same bucket.
+  // - They should be in a single range bucket [-10, -10], and another bucket
+  //   [-9, 10] with empty data should be created after it.
+  ASSERT_THAT(results, SizeIs(2));
+  // Bucket 0: key lower = -10, key upper = -10, keys = [-10, -10, -10, -10,
+  // -10].
+  EXPECT_THAT(results[0].key_lower, Eq(-10));
+  EXPECT_THAT(results[0].key_upper, Eq(-10));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[0].start, results[0].end),
+      ElementsAre(
+          IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+          IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+          IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+          IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+          IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10)));
+  // Bucket 1: key lower = -9, key upper = 10, keys = [].
+  EXPECT_THAT(results[1].key_lower, Eq(-9));
+  EXPECT_THAT(results[1].key_upper, Eq(10));
+  EXPECT_THAT(std::vector<IntegerIndexData>(results[1].start, results[1].end),
+              IsEmpty());
+}
+
+TEST(IntegerIndexBucketUtilTest,
+     Split_sameKeysExceedingThreshold_singleBucket_keyWithinKeyLowerAndUpper) {
+  std::vector<IntegerIndexData> data = {
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 0),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 0),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 0),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 0),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 0)};
+
+  // Keys = [0, 0, 0, 0, 0].
+  std::vector<DataRangeAndBucketInfo> results =
+      Split(data, /*original_key_lower=*/-10, /*original_key_upper=*/10,
+            /*num_data_threshold=*/3);
+  // - Even though # of data with key = 0 exceeds the threshold, they should
+  //   still be in the same bucket.
+  // - They should be in a single range bucket [0, 0]. Another bucket [-10, -1]
+  //   with empty data should be created before it, and another bucket [1, 10]
+  //   with empty data should be created after it.
+  ASSERT_THAT(results, SizeIs(3));
+  // Bucket 0: key lower = -10, key upper = -1, keys = [].
+  EXPECT_THAT(results[0].key_lower, Eq(-10));
+  EXPECT_THAT(results[0].key_upper, Eq(-1));
+  EXPECT_THAT(std::vector<IntegerIndexData>(results[0].start, results[0].end),
+              IsEmpty());
+  // Bucket 1: key lower = 0, key upper = 0, keys = [0, 0, 0, 0, 0].
+  EXPECT_THAT(results[1].key_lower, Eq(0));
+  EXPECT_THAT(results[1].key_upper, Eq(0));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[1].start, results[1].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 0),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 0),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 0),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 0),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 0)));
+  // Bucket 2: key lower = 1, key upper = 10, keys = [].
+  EXPECT_THAT(results[2].key_lower, Eq(1));
+  EXPECT_THAT(results[2].key_upper, Eq(10));
+  EXPECT_THAT(std::vector<IntegerIndexData>(results[2].start, results[2].end),
+              IsEmpty());
+}
+
+TEST(IntegerIndexBucketUtilTest,
+     Split_sameKeysExceedingThreshold_singleBucket_keyEqualsKeyUpper) {
+  std::vector<IntegerIndexData> data = {
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10)};
+
+  // Keys = [10, 10, 10, 10, 10].
+  std::vector<DataRangeAndBucketInfo> results =
+      Split(data, /*original_key_lower=*/-10, /*original_key_upper=*/10,
+            /*num_data_threshold=*/3);
+  // - Even though # of data with key = 10 exceeds the threshold, they should
+  //   still be in the same bucket.
+  // - They should be in a single range bucket [10, 10], and another bucket
+  //   [-10, 9] with empty data should be created before it.
+  ASSERT_THAT(results, SizeIs(2));
+  // Bucket 0: key lower = -10, key upper = 9, keys = [].
+  EXPECT_THAT(results[0].key_lower, Eq(-10));
+  EXPECT_THAT(results[0].key_upper, Eq(9));
+  EXPECT_THAT(std::vector<IntegerIndexData>(results[0].start, results[0].end),
+              IsEmpty());
+  // Bucket 1: key lower = -10, key upper = 10, keys = [10, 10, 10, 10, 10].
+  EXPECT_THAT(results[1].key_lower, Eq(10));
+  EXPECT_THAT(results[1].key_upper, Eq(10));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[1].start, results[1].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10)));
+}
+
+TEST(IntegerIndexBucketUtilTest,
+     Split_adjacentKeysTotalNumDataExceedThreshold) {
+  std::vector<IntegerIndexData> data = {
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -1),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -1),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10)};
+
+  // Keys = [-10, -10, -1, -1, 2, 2, 10, 10].
+  std::vector<DataRangeAndBucketInfo> results =
+      Split(data, /*original_key_lower=*/-10, /*original_key_upper=*/10,
+            /*num_data_threshold=*/3);
+  // Even though # of data with the same key is within the threshold, since
+  // total # of data of adjacent keys exceed the threshold, they should be
+  // separated into different buckets.
+  ASSERT_THAT(results, SizeIs(4));
+  // Bucket 0: key lower = -10, key upper = -10, keys = [-10, -10].
+  EXPECT_THAT(results[0].key_lower, Eq(-10));
+  EXPECT_THAT(results[0].key_upper, Eq(-10));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[0].start, results[0].end),
+      ElementsAre(
+          IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+          IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10)));
+  // Bucket 1: key lower = -9, key upper = -1, keys = [-1, -1].
+  EXPECT_THAT(results[1].key_lower, Eq(-9));
+  EXPECT_THAT(results[1].key_upper, Eq(-1));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[1].start, results[1].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -1),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -1)));
+  // Bucket 2: key lower = 0, key upper = 2, keys = [2, 2].
+  EXPECT_THAT(results[2].key_lower, Eq(0));
+  EXPECT_THAT(results[2].key_upper, Eq(2));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[2].start, results[2].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2)));
+  // Bucket 3: key lower = 3, key upper = 10, keys = [10, 10].
+  EXPECT_THAT(results[3].key_lower, Eq(3));
+  EXPECT_THAT(results[3].key_upper, Eq(10));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[3].start, results[3].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10)));
+}
+
+TEST(IntegerIndexBucketUtilTest,
+     Split_keyLowerEqualsIntMin_smallestKeyGreaterThanKeyLower) {
+  std::vector<IntegerIndexData> data = {
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId,
+                       std::numeric_limits<int64_t>::min() + 1),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -1),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10)};
+
+  // Keys = [INT64_MIN + 1, -10, -1, 2, 10].
+  std::vector<DataRangeAndBucketInfo> results =
+      Split(data, /*original_key_lower=*/std::numeric_limits<int64_t>::min(),
+            /*original_key_upper=*/std::numeric_limits<int64_t>::max(),
+            /*num_data_threshold=*/3);
+  ASSERT_THAT(results, SizeIs(2));
+  // Bucket 0: key lower = INT64_MIN, key upper = -1, keys = [INT64_MIN + 1,
+  // -10, -1].
+  EXPECT_THAT(results[0].key_lower, Eq(std::numeric_limits<int64_t>::min()));
+  EXPECT_THAT(results[0].key_upper, Eq(-1));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[0].start, results[0].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId,
+                                   std::numeric_limits<int64_t>::min() + 1),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -1)));
+  // Bucket 1: key lower = 0, key upper = INT64_MAX, keys = [2, 10].
+  EXPECT_THAT(results[1].key_lower, Eq(0));
+  EXPECT_THAT(results[1].key_upper, Eq(std::numeric_limits<int64_t>::max()));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[1].start, results[1].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10)));
+}
+
+TEST(IntegerIndexBucketUtilTest,
+     Split_keyLowerEqualsIntMin_smallestKeyEqualsKeyLower) {
+  std::vector<IntegerIndexData> data = {
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId,
+                       std::numeric_limits<int64_t>::min()),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -1),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10)};
+
+  // Keys = [INT64_MIN, -10, -1, 2, 10].
+  std::vector<DataRangeAndBucketInfo> results =
+      Split(data, /*original_key_lower=*/std::numeric_limits<int64_t>::min(),
+            /*original_key_upper=*/std::numeric_limits<int64_t>::max(),
+            /*num_data_threshold=*/3);
+  ASSERT_THAT(results, SizeIs(2));
+  // Bucket 0: key lower = INT64_MIN, key upper = -1, keys = [INT64_MIN, -10,
+  // -1].
+  EXPECT_THAT(results[0].key_lower, Eq(std::numeric_limits<int64_t>::min()));
+  EXPECT_THAT(results[0].key_upper, Eq(-1));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[0].start, results[0].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId,
+                                   std::numeric_limits<int64_t>::min()),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -1)));
+  // Bucket 1: key lower = 0, key upper = INT64_MAX, keys = [2, 10].
+  EXPECT_THAT(results[1].key_lower, Eq(0));
+  EXPECT_THAT(results[1].key_upper, Eq(std::numeric_limits<int64_t>::max()));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[1].start, results[1].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10)));
+}
+
+TEST(IntegerIndexBucketUtilTest,
+     Split_keyLowerEqualsIntMin_keyIntMinExceedingThreshold) {
+  std::vector<IntegerIndexData> data = {
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId,
+                       std::numeric_limits<int64_t>::min()),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId,
+                       std::numeric_limits<int64_t>::min()),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId,
+                       std::numeric_limits<int64_t>::min()),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId,
+                       std::numeric_limits<int64_t>::min()),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId,
+                       std::numeric_limits<int64_t>::min()),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -1),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10)};
+
+  // Keys = [INT64_MIN, INT64_MIN, INT64_MIN, INT64_MIN, INT64_MIN, -10, -1, 2,
+  // 10].
+  std::vector<DataRangeAndBucketInfo> results =
+      Split(data, /*original_key_lower=*/std::numeric_limits<int64_t>::min(),
+            /*original_key_upper=*/std::numeric_limits<int64_t>::max(),
+            /*num_data_threshold=*/3);
+  ASSERT_THAT(results, SizeIs(3));
+  // Bucket 0: key lower = INT64_MIN, key upper = INT64_MIN, keys = [INT64_MIN,
+  // INT64_MIN, INT64_MIN, INT64_MIN, INT64_MIN].
+  EXPECT_THAT(results[0].key_lower, Eq(std::numeric_limits<int64_t>::min()));
+  EXPECT_THAT(results[0].key_upper, Eq(std::numeric_limits<int64_t>::min()));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[0].start, results[0].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId,
+                                   std::numeric_limits<int64_t>::min()),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId,
+                                   std::numeric_limits<int64_t>::min()),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId,
+                                   std::numeric_limits<int64_t>::min()),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId,
+                                   std::numeric_limits<int64_t>::min()),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId,
+                                   std::numeric_limits<int64_t>::min())));
+  // Bucket 1: key lower = INT64_MIN + 1, key upper = 2, keys = [-10, -1, 2].
+  EXPECT_THAT(results[1].key_lower,
+              Eq(std::numeric_limits<int64_t>::min() + 1));
+  EXPECT_THAT(results[1].key_upper, Eq(2));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[1].start, results[1].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -1),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2)));
+  // Bucket 2: key lower = 3, key upper = INT64_MAX, keys = [10].
+  EXPECT_THAT(results[2].key_lower, Eq(3));
+  EXPECT_THAT(results[2].key_upper, Eq(std::numeric_limits<int64_t>::max()));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[2].start, results[2].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10)));
+}
+
+TEST(IntegerIndexBucketUtilTest,
+     Split_keyUpperEqualsIntMax_largestKeySmallerThanKeyUpper) {
+  std::vector<IntegerIndexData> data = {
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -1),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId,
+                       std::numeric_limits<int64_t>::max() - 1),
+  };
+
+  // Keys = [-10, -1, 2, 10, INT64_MAX - 1].
+  std::vector<DataRangeAndBucketInfo> results =
+      Split(data, /*original_key_lower=*/std::numeric_limits<int64_t>::min(),
+            /*original_key_upper=*/std::numeric_limits<int64_t>::max(),
+            /*num_data_threshold=*/3);
+  ASSERT_THAT(results, SizeIs(2));
+  // Bucket 0: key lower = INT64_MIN, key upper = 2, keys = [-10, -1, 2].
+  EXPECT_THAT(results[0].key_lower, Eq(std::numeric_limits<int64_t>::min()));
+  EXPECT_THAT(results[0].key_upper, Eq(2));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[0].start, results[0].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -1),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2)));
+  // Bucket 1: key lower = 3, key upper = INT64_MAX, keys = [10, INT64_MAX - 1].
+  EXPECT_THAT(results[1].key_lower, Eq(3));
+  EXPECT_THAT(results[1].key_upper, Eq(std::numeric_limits<int64_t>::max()));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[1].start, results[1].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId,
+                                   std::numeric_limits<int64_t>::max() - 1)));
+}
+
+TEST(IntegerIndexBucketUtilTest,
+     Split_keyUpperEqualsIntMax_largestKeyEqualsKeyUpper) {
+  std::vector<IntegerIndexData> data = {
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -1),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId,
+                       std::numeric_limits<int64_t>::max()),
+  };
+
+  // Keys = [-10, -1, 2, 10, INT64_MAX].
+  std::vector<DataRangeAndBucketInfo> results =
+      Split(data, /*original_key_lower=*/std::numeric_limits<int64_t>::min(),
+            /*original_key_upper=*/std::numeric_limits<int64_t>::max(),
+            /*num_data_threshold=*/3);
+  ASSERT_THAT(results, SizeIs(2));
+  // Bucket 0: key lower = INT64_MIN, key upper = 2, keys = [-10, -1, 2].
+  EXPECT_THAT(results[0].key_lower, Eq(std::numeric_limits<int64_t>::min()));
+  EXPECT_THAT(results[0].key_upper, Eq(2));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[0].start, results[0].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -1),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2)));
+  // Bucket 1: key lower = 3, key upper = INT64_MAX, keys = [10, INT64_MAX].
+  EXPECT_THAT(results[1].key_lower, Eq(3));
+  EXPECT_THAT(results[1].key_upper, Eq(std::numeric_limits<int64_t>::max()));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[1].start, results[1].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId,
+                                   std::numeric_limits<int64_t>::max())));
+}
+
+TEST(IntegerIndexBucketUtilTest,
+     Split_keyUpperEqualsIntMax_keyIntMaxExceedingThreshold) {
+  std::vector<IntegerIndexData> data = {
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -1),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId,
+                       std::numeric_limits<int64_t>::max()),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId,
+                       std::numeric_limits<int64_t>::max()),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId,
+                       std::numeric_limits<int64_t>::max()),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId,
+                       std::numeric_limits<int64_t>::max()),
+      IntegerIndexData(kDefaultSectionId, kDefaultDocumentId,
+                       std::numeric_limits<int64_t>::max())};
+
+  // Keys = [-10, -1, 2, 10, INT64_MAX, INT64_MAX, INT64_MAX, INT64_MAX,
+  // INT64_MAX].
+  std::vector<DataRangeAndBucketInfo> results =
+      Split(data, /*original_key_lower=*/std::numeric_limits<int64_t>::min(),
+            /*original_key_upper=*/std::numeric_limits<int64_t>::max(),
+            /*num_data_threshold=*/3);
+  ASSERT_THAT(results, SizeIs(3));
+  // Bucket 0: key lower = INT64_MIN, key upper = 2, keys = [-10, -1, 2].
+  EXPECT_THAT(results[0].key_lower, Eq(std::numeric_limits<int64_t>::min()));
+  EXPECT_THAT(results[0].key_upper, Eq(2));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[0].start, results[0].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -10),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, -1),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 2)));
+  // Bucket 1: key lower = 3, key upper = INT_MAX - 1, keys = [10].
+  EXPECT_THAT(results[1].key_lower, Eq(3));
+  EXPECT_THAT(results[1].key_upper,
+              Eq(std::numeric_limits<int64_t>::max() - 1));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[1].start, results[1].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId, 10)));
+  // Bucket 2: key lower = INT64_MAX, key upper = INT64_MAX, keys = [INT64_MAX,
+  // INT64_MAX, INT64_MAX, INT64_MAX, INT64_MAX].
+  EXPECT_THAT(results[2].key_lower, Eq(std::numeric_limits<int64_t>::max()));
+  EXPECT_THAT(results[2].key_upper, Eq(std::numeric_limits<int64_t>::max()));
+  EXPECT_THAT(
+      std::vector<IntegerIndexData>(results[2].start, results[2].end),
+      ElementsAre(IntegerIndexData(kDefaultSectionId, kDefaultDocumentId,
+                                   std::numeric_limits<int64_t>::max()),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId,
+                                   std::numeric_limits<int64_t>::max()),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId,
+                                   std::numeric_limits<int64_t>::max()),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId,
+                                   std::numeric_limits<int64_t>::max()),
+                  IntegerIndexData(kDefaultSectionId, kDefaultDocumentId,
+                                   std::numeric_limits<int64_t>::max())));
+}
+
+}  // namespace
+
+}  // namespace integer_index_bucket_util
+}  // namespace lib
+}  // namespace icing
diff --git a/icing/index/numeric/integer-index-storage.cc b/icing/index/numeric/integer-index-storage.cc
index 22ef8bd..db1983c 100644
--- a/icing/index/numeric/integer-index-storage.cc
+++ b/icing/index/numeric/integer-index-storage.cc
@@ -17,6 +17,7 @@
 #include <algorithm>
 #include <cstdint>
 #include <functional>
+#include <iterator>
 #include <limits>
 #include <memory>
 #include <queue>
@@ -37,6 +38,7 @@
 #include "icing/index/hit/doc-hit-info.h"
 #include "icing/index/iterator/doc-hit-info-iterator.h"
 #include "icing/index/numeric/doc-hit-info-iterator-numeric.h"
+#include "icing/index/numeric/integer-index-bucket-util.h"
 #include "icing/index/numeric/integer-index-data.h"
 #include "icing/index/numeric/numeric-index.h"
 #include "icing/index/numeric/posting-list-integer-index-accessor.h"
@@ -50,6 +52,41 @@ namespace lib {
 
 namespace {
 
+// Helper function to flush data between [it_start, it_end) into posting list(s)
+// and return posting list id.
+// Note: it will sort data between [it_start, it_end) by basic hit value, so the
+// caller should be aware that the data order will be changed after calling this
+// function.
+libtextclassifier3::StatusOr<PostingListIdentifier> FlushDataIntoPostingLists(
+    FlashIndexStorage* flash_index_storage,
+    PostingListIntegerIndexSerializer* posting_list_serializer,
+    const std::vector<IntegerIndexData>::iterator& it_start,
+    const std::vector<IntegerIndexData>::iterator& it_end) {
+  if (it_start == it_end) {
+    return PostingListIdentifier::kInvalid;
+  }
+
+  ICING_ASSIGN_OR_RETURN(
+      std::unique_ptr<PostingListIntegerIndexAccessor> new_pl_accessor,
+      PostingListIntegerIndexAccessor::Create(flash_index_storage,
+                                              posting_list_serializer));
+
+  std::sort(it_start, it_end);
+  for (auto it = it_end - 1; it >= it_start; --it) {
+    ICING_RETURN_IF_ERROR(new_pl_accessor->PrependData(*it));
+  }
+
+  PostingListAccessor::FinalizeResult result =
+      std::move(*new_pl_accessor).Finalize();
+  if (!result.status.ok()) {
+    return result.status;
+  }
+  if (!result.id.is_valid()) {
+    return absl_ports::InternalError("Fail to flush data into posting list(s)");
+  }
+  return result.id;
+}
+
 // The following 4 methods are helper functions to get the correct file path of
 // metadata/sorted_buckets/unsorted_buckets/flash_index_storage, according to
 // the given working directory.
@@ -510,9 +547,12 @@ libtextclassifier3::Status IntegerIndexStorage::AddKeys(
     mutable_new_arr.SetArray(/*idx=*/0, new_buckets.data(), new_buckets.size());
   }
 
-  // Step 4: merge the unsorted bucket array into the sorted bucket array if the
-  //         length of the unsorted bucket array exceeds the threshold.
-  // TODO(b/259743562): [Optimization 1] implement merge
+  // Step 4: sort and merge the unsorted bucket array into the sorted bucket
+  //         array if the length of the unsorted bucket array exceeds the
+  //         threshold.
+  if (unsorted_buckets_->num_elements() > kUnsortedBucketsLengthThreshold) {
+    ICING_RETURN_IF_ERROR(SortBuckets());
+  }
 
   info().num_data += new_keys.size();
 
@@ -679,29 +719,23 @@ IntegerIndexStorage::InitializeNewFiles(
         absl_ports::StrCat("Failed to create directory: ", working_path));
   }
 
-  // TODO(b/259743562): [Optimization 1] decide max # buckets, unsorted buckets
-  //                    threshold
   // Initialize sorted_buckets
   int32_t pre_mapping_mmap_size = sizeof(Bucket) * (1 << 10);
-  int32_t max_file_size =
-      pre_mapping_mmap_size + FileBackedVector<Bucket>::Header::kHeaderSize;
   ICING_ASSIGN_OR_RETURN(
       std::unique_ptr<FileBackedVector<Bucket>> sorted_buckets,
       FileBackedVector<Bucket>::Create(
           filesystem, GetSortedBucketsFilePath(working_path),
-          MemoryMappedFile::Strategy::READ_WRITE_AUTO_SYNC, max_file_size,
-          pre_mapping_mmap_size));
+          MemoryMappedFile::Strategy::READ_WRITE_AUTO_SYNC,
+          FileBackedVector<Bucket>::kMaxFileSize, pre_mapping_mmap_size));
 
   // Initialize unsorted_buckets
-  pre_mapping_mmap_size = sizeof(Bucket) * 100;
-  max_file_size =
-      pre_mapping_mmap_size + FileBackedVector<Bucket>::Header::kHeaderSize;
+  pre_mapping_mmap_size = sizeof(Bucket) * kUnsortedBucketsLengthThreshold;
   ICING_ASSIGN_OR_RETURN(
       std::unique_ptr<FileBackedVector<Bucket>> unsorted_buckets,
       FileBackedVector<Bucket>::Create(
           filesystem, GetUnsortedBucketsFilePath(working_path),
-          MemoryMappedFile::Strategy::READ_WRITE_AUTO_SYNC, max_file_size,
-          pre_mapping_mmap_size));
+          MemoryMappedFile::Strategy::READ_WRITE_AUTO_SYNC,
+          FileBackedVector<Bucket>::kMaxFileSize, pre_mapping_mmap_size));
 
   // Initialize flash_index_storage
   ICING_ASSIGN_OR_RETURN(
@@ -785,29 +819,23 @@ IntegerIndexStorage::InitializeExistingFiles(
                                /*pre_mapping_file_offset=*/0,
                                /*pre_mapping_mmap_size=*/kMetadataFileSize));
 
-  // TODO(b/259743562): [Optimization 1] decide max # buckets, unsorted buckets
-  //                    threshold
   // Initialize sorted_buckets
   int32_t pre_mapping_mmap_size = sizeof(Bucket) * (1 << 10);
-  int32_t max_file_size =
-      pre_mapping_mmap_size + FileBackedVector<Bucket>::Header::kHeaderSize;
   ICING_ASSIGN_OR_RETURN(
       std::unique_ptr<FileBackedVector<Bucket>> sorted_buckets,
       FileBackedVector<Bucket>::Create(
           filesystem, GetSortedBucketsFilePath(working_path),
-          MemoryMappedFile::Strategy::READ_WRITE_AUTO_SYNC, max_file_size,
-          pre_mapping_mmap_size));
+          MemoryMappedFile::Strategy::READ_WRITE_AUTO_SYNC,
+          FileBackedVector<Bucket>::kMaxFileSize, pre_mapping_mmap_size));
 
   // Initialize unsorted_buckets
-  pre_mapping_mmap_size = sizeof(Bucket) * 100;
-  max_file_size =
-      pre_mapping_mmap_size + FileBackedVector<Bucket>::Header::kHeaderSize;
+  pre_mapping_mmap_size = sizeof(Bucket) * kUnsortedBucketsLengthThreshold;
   ICING_ASSIGN_OR_RETURN(
       std::unique_ptr<FileBackedVector<Bucket>> unsorted_buckets,
       FileBackedVector<Bucket>::Create(
           filesystem, GetUnsortedBucketsFilePath(working_path),
-          MemoryMappedFile::Strategy::READ_WRITE_AUTO_SYNC, max_file_size,
-          pre_mapping_mmap_size));
+          MemoryMappedFile::Strategy::READ_WRITE_AUTO_SYNC,
+          FileBackedVector<Bucket>::kMaxFileSize, pre_mapping_mmap_size));
 
   // Initialize flash_index_storage
   ICING_ASSIGN_OR_RETURN(
@@ -845,28 +873,13 @@ IntegerIndexStorage::FlushDataIntoNewSortedBucket(
   }
 
   ICING_ASSIGN_OR_RETURN(
-      std::unique_ptr<PostingListIntegerIndexAccessor> new_pl_accessor,
-      PostingListIntegerIndexAccessor::Create(
-          storage->flash_index_storage_.get(),
-          storage->posting_list_serializer_));
-
-  std::sort(data.begin(), data.end());
-  for (auto itr = data.rbegin(); itr != data.rend(); ++itr) {
-    ICING_RETURN_IF_ERROR(new_pl_accessor->PrependData(*itr));
-  }
-
-  PostingListAccessor::FinalizeResult result =
-      std::move(*new_pl_accessor).Finalize();
-  if (!result.status.ok()) {
-    return result.status;
-  }
-  if (!result.id.is_valid()) {
-    return absl_ports::InternalError("Fail to flush data into posting list");
-  }
+      PostingListIdentifier pl_id,
+      FlushDataIntoPostingLists(storage->flash_index_storage_.get(),
+                                storage->posting_list_serializer_, data.begin(),
+                                data.end()));
 
   storage->info().num_data += data.size();
-  return storage->sorted_buckets_->Append(
-      Bucket(key_lower, key_upper, result.id));
+  return storage->sorted_buckets_->Append(Bucket(key_lower, key_upper, pl_id));
 }
 
 libtextclassifier3::Status IntegerIndexStorage::PersistStoragesToDisk() {
@@ -921,21 +934,80 @@ IntegerIndexStorage::AddKeysIntoBucketAndSplitIfNecessary(
   }
 
   for (auto it = it_start; it != it_end; ++it) {
-    // TODO(b/259743562): [Optimization 1] implement split bucket if pl is full
-    //                    and the bucket is splittable
+    if (mutable_bucket.Get().key_lower() < mutable_bucket.Get().key_upper() &&
+        pl_accessor->WantsSplit()) {
+      // If the bucket needs split (max size and full) and is splittable, then
+      // we perform bucket splitting.
+
+      // 1. Finalize the current posting list accessor.
+      PostingListAccessor::FinalizeResult result =
+          std::move(*pl_accessor).Finalize();
+      if (!result.status.ok()) {
+        return result.status;
+      }
+
+      // 2. Create another posting list accessor instance. Read all data and
+      //    free all posting lists.
+      ICING_ASSIGN_OR_RETURN(
+          pl_accessor,
+          PostingListIntegerIndexAccessor::CreateFromExisting(
+              flash_index_storage_.get(), posting_list_serializer_, result.id));
+      ICING_ASSIGN_OR_RETURN(std::vector<IntegerIndexData> all_data,
+                             pl_accessor->GetAllDataAndFree());
+
+      // 3. Append all remaining new data.
+      all_data.reserve(all_data.size() + std::distance(it, it_end));
+      for (; it != it_end; ++it) {
+        all_data.push_back(IntegerIndexData(section_id, document_id, *it));
+      }
+
+      // 4. Run bucket splitting algorithm to decide new buckets and dispatch
+      //    data.
+      std::vector<integer_index_bucket_util::DataRangeAndBucketInfo>
+          new_bucket_infos = integer_index_bucket_util::Split(
+              all_data, mutable_bucket.Get().key_lower(),
+              mutable_bucket.Get().key_upper(),
+              kNumDataThresholdForBucketSplit);
+      if (new_bucket_infos.empty()) {
+        ICING_LOG(WARNING)
+            << "No buckets after splitting. This should not happen.";
+        return absl_ports::InternalError("Split error");
+      }
+
+      // 5. Flush data.
+      std::vector<Bucket> new_buckets;
+      for (int i = 0; i < new_bucket_infos.size(); ++i) {
+        ICING_ASSIGN_OR_RETURN(
+            PostingListIdentifier pl_id,
+            FlushDataIntoPostingLists(
+                flash_index_storage_.get(), posting_list_serializer_,
+                new_bucket_infos[i].start, new_bucket_infos[i].end));
+        if (i == 0) {
+          // Reuse mutable_bucket
+          mutable_bucket.Get().set_key_lower(new_bucket_infos[i].key_lower);
+          mutable_bucket.Get().set_key_upper(new_bucket_infos[i].key_upper);
+          mutable_bucket.Get().set_posting_list_identifier(pl_id);
+        } else {
+          new_buckets.push_back(Bucket(new_bucket_infos[i].key_lower,
+                                       new_bucket_infos[i].key_upper, pl_id));
+        }
+      }
+
+      return new_buckets;
+    }
+
     ICING_RETURN_IF_ERROR(pl_accessor->PrependData(
         IntegerIndexData(section_id, document_id, *it)));
   }
 
-  // TODO(b/259743562): [Optimization 1] implement split and return new buckets.
-  //                    We will change the original bucket (mutable_bucket)
-  //                    in-place to one of the new buckets, and the rest will
-  //                    be returned and added into unsorted buckets in AddKeys.
   PostingListAccessor::FinalizeResult result =
       std::move(*pl_accessor).Finalize();
   if (!result.status.ok()) {
     return result.status;
   }
+  if (!result.id.is_valid()) {
+    return absl_ports::InternalError("Fail to flush data into posting list(s)");
+  }
 
   mutable_bucket.Get().set_posting_list_identifier(result.id);
 
diff --git a/icing/index/numeric/integer-index-storage.h b/icing/index/numeric/integer-index-storage.h
index be0add9..ddd9231 100644
--- a/icing/index/numeric/integer-index-storage.h
+++ b/icing/index/numeric/integer-index-storage.h
@@ -30,6 +30,7 @@
 #include "icing/file/posting_list/flash-index-storage.h"
 #include "icing/file/posting_list/posting-list-identifier.h"
 #include "icing/index/iterator/doc-hit-info-iterator.h"
+#include "icing/index/numeric/integer-index-data.h"
 #include "icing/index/numeric/posting-list-integer-index-serializer.h"
 #include "icing/schema/section.h"
 #include "icing/store/document-id.h"
@@ -117,6 +118,10 @@ class IntegerIndexStorage : public PersistentStorage {
 
     int64_t key_upper() const { return key_upper_; }
 
+    void set_key_lower(int64_t key_lower) { key_lower_ = key_lower; }
+
+    void set_key_upper(int64_t key_upper) { key_upper_ = key_upper; }
+
     PostingListIdentifier posting_list_identifier() const {
       return posting_list_identifier_;
     }
@@ -176,14 +181,29 @@ class IntegerIndexStorage : public PersistentStorage {
       WorkingPathType::kDirectory;
   static constexpr std::string_view kFilePrefix = "integer_index_storage";
 
-  // # of data threshold for bucket merging. If total # data of adjacent buckets
-  // exceed this value, then flush the accumulated data. Otherwise merge
-  // buckets and their data.
+  // # of data threshold for bucket merging during optimization (TransferIndex).
+  // If total # data of adjacent buckets exceed this value, then flush the
+  // accumulated data. Otherwise merge buckets and their data.
   //
   // Calculated by: 0.7 * (kMaxPostingListSize / sizeof(IntegerIndexData)),
   // where kMaxPostingListSize = (kPageSize - sizeof(IndexBlock::BlockHeader)).
   static constexpr int32_t kNumDataThresholdForBucketMerge = 240;
 
+  // # of data threshold for bucket splitting during indexing (AddKeys).
+  // When the posting list of a bucket is full, we will try to split data into
+  // multiple buckets according to their keys. In order to achieve good
+  // (amortized) time complexity, we want # of data in new buckets to be at most
+  // half # of elements in a full posting list.
+  //
+  // Calculated by: 0.5 * (kMaxPostingListSize / sizeof(IntegerIndexData)),
+  // where kMaxPostingListSize = (kPageSize - sizeof(IndexBlock::BlockHeader)).
+  static constexpr int32_t kNumDataThresholdForBucketSplit = 170;
+
+  // Length threshold to sort and merge unsorted buckets into sorted buckets. If
+  // the length of unsorted_buckets exceed the threshold, then call
+  // SortBuckets().
+  static constexpr int32_t kUnsortedBucketsLengthThreshold = 50;
+
   // Creates a new IntegerIndexStorage instance to index integers (for a single
   // property). If any of the underlying file is missing, then delete the whole
   // working_path and (re)initialize with new ones. Otherwise initialize and
@@ -370,7 +390,6 @@ class IntegerIndexStorage : public PersistentStorage {
   //     into several new buckets with new ranges, and split the data (according
   //     to their keys and the range of new buckets) of the original posting
   //     list into several new posting lists.
-  //     TODO(b/259743562): [Optimization 1] implement split
   //   - Otherwise, just simply add a new key into it, and PostingListAccessor
   //     mechanism will automatically create a new max size posting list and
   //     chain them.
diff --git a/icing/index/numeric/integer-index-storage_benchmark.cc b/icing/index/numeric/integer-index-storage_benchmark.cc
index d150f2d..54b19c3 100644
--- a/icing/index/numeric/integer-index-storage_benchmark.cc
+++ b/icing/index/numeric/integer-index-storage_benchmark.cc
@@ -57,6 +57,7 @@ namespace lib {
 namespace {
 
 using ::testing::Eq;
+using ::testing::IsEmpty;
 using ::testing::SizeIs;
 
 static constexpr SectionId kDefaultSectionId = 12;
@@ -237,18 +238,24 @@ void BM_ExactQuery(benchmark::State& state) {
         std::unique_ptr<DocHitInfoIterator> iterator,
         storage->GetIterator(/*query_key_lower=*/exact_query_key,
                              /*query_key_upper=*/exact_query_key));
-    int cnt = 0;
+    std::vector<DocHitInfo> data;
     while (iterator->Advance().ok()) {
-      benchmark::DoNotOptimize(iterator->doc_hit_info());
-      ++cnt;
+      data.push_back(iterator->doc_hit_info());
     }
 
+    state.PauseTiming();
     const auto it = keys.find(exact_query_key);
     if (it == keys.end()) {
-      ASSERT_THAT(cnt, Eq(0));
+      ASSERT_THAT(data, IsEmpty());
     } else {
-      ASSERT_THAT(it->second, SizeIs(cnt));
+      ASSERT_THAT(data, SizeIs(it->second.size()));
+      std::reverse(data.begin(), data.end());
+      for (int i = 0; i < data.size(); ++i) {
+        ASSERT_THAT(data[i].document_id(), Eq(it->second[i]));
+        ASSERT_THAT(data[i].hit_section_ids_mask(), Eq(1 << kDefaultSectionId));
+      }
     }
+    state.ResumeTiming();
   }
 }
 BENCHMARK(BM_ExactQuery)
diff --git a/icing/index/numeric/integer-index-storage_test.cc b/icing/index/numeric/integer-index-storage_test.cc
index 9d6864c..ed7d5db 100644
--- a/icing/index/numeric/integer-index-storage_test.cc
+++ b/icing/index/numeric/integer-index-storage_test.cc
@@ -14,6 +14,8 @@
 
 #include "icing/index/numeric/integer-index-storage.h"
 
+#include <unistd.h>
+
 #include <cstdint>
 #include <limits>
 #include <memory>
@@ -26,7 +28,10 @@
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 #include "icing/file/file-backed-vector.h"
+#include "icing/file/filesystem.h"
 #include "icing/file/persistent-storage.h"
+#include "icing/file/posting_list/flash-index-storage.h"
+#include "icing/file/posting_list/index-block.h"
 #include "icing/file/posting_list/posting-list-identifier.h"
 #include "icing/index/hit/doc-hit-info.h"
 #include "icing/index/iterator/doc-hit-info-iterator.h"
@@ -42,14 +47,17 @@ namespace lib {
 
 namespace {
 
+using ::testing::Contains;
 using ::testing::ElementsAre;
 using ::testing::ElementsAreArray;
 using ::testing::Eq;
+using ::testing::Ge;
 using ::testing::Gt;
 using ::testing::HasSubstr;
 using ::testing::IsEmpty;
 using ::testing::IsFalse;
 using ::testing::IsTrue;
+using ::testing::Key;
 using ::testing::Le;
 using ::testing::Ne;
 using ::testing::Not;
@@ -1186,6 +1194,150 @@ TEST_F(IntegerIndexStorageTest,
           EqualsDocHitInfo(kDefaultDocumentId, expected_sections))));
 }
 
+TEST_F(IntegerIndexStorageTest, SplitBuckets) {
+  ICING_ASSERT_OK_AND_ASSIGN(
+      std::unique_ptr<IntegerIndexStorage> storage,
+      IntegerIndexStorage::Create(filesystem_, working_path_, Options(),
+                                  serializer_.get()));
+
+  uint32_t block_size = FlashIndexStorage::SelectBlockSize();
+  uint32_t max_posting_list_bytes = IndexBlock::CalculateMaxPostingListBytes(
+      block_size, serializer_->GetDataTypeBytes());
+  uint32_t max_num_data_before_split =
+      max_posting_list_bytes / serializer_->GetDataTypeBytes();
+
+  // Add max_num_data_before_split + 1 keys to invoke bucket splitting.
+  // Keys: max_num_data_before_split to 0
+  // Document ids: 0 to max_num_data_before_split
+  std::unordered_map<int64_t, DocumentId> data;
+  int64_t key = max_num_data_before_split;
+  DocumentId document_id = 0;
+  for (int i = 0; i < max_num_data_before_split + 1; ++i) {
+    data[key] = document_id;
+    ICING_ASSERT_OK(
+        storage->AddKeys(document_id, kDefaultSectionId, /*new_keys=*/{key}));
+    ++document_id;
+    --key;
+  }
+  ICING_ASSERT_OK(storage->PersistToDisk());
+
+  // Manually check sorted and unsorted buckets.
+  {
+    // Check sorted buckets.
+    const std::string sorted_buckets_file_path = absl_ports::StrCat(
+        working_path_, "/", IntegerIndexStorage::kFilePrefix, ".s");
+    ICING_ASSERT_OK_AND_ASSIGN(
+        std::unique_ptr<FileBackedVector<Bucket>> sorted_buckets,
+        FileBackedVector<Bucket>::Create(
+            filesystem_, sorted_buckets_file_path,
+            MemoryMappedFile::Strategy::READ_WRITE_AUTO_SYNC));
+
+    EXPECT_THAT(sorted_buckets->num_elements(), Eq(1));
+    ICING_ASSERT_OK_AND_ASSIGN(const Bucket* bucket1,
+                               sorted_buckets->Get(/*idx=*/0));
+    EXPECT_THAT(bucket1->key_lower(), Eq(std::numeric_limits<int64_t>::min()));
+    EXPECT_THAT(bucket1->key_upper(), Ne(std::numeric_limits<int64_t>::max()));
+
+    int64_t sorted_bucket_key_upper = bucket1->key_upper();
+
+    // Check unsorted buckets.
+    const std::string unsorted_buckets_file_path = absl_ports::StrCat(
+        working_path_, "/", IntegerIndexStorage::kFilePrefix, ".u");
+    ICING_ASSERT_OK_AND_ASSIGN(
+        std::unique_ptr<FileBackedVector<Bucket>> unsorted_buckets,
+        FileBackedVector<Bucket>::Create(
+            filesystem_, unsorted_buckets_file_path,
+            MemoryMappedFile::Strategy::READ_WRITE_AUTO_SYNC));
+
+    EXPECT_THAT(unsorted_buckets->num_elements(), Ge(1));
+    ICING_ASSERT_OK_AND_ASSIGN(const Bucket* bucket2,
+                               unsorted_buckets->Get(/*idx=*/0));
+    EXPECT_THAT(bucket2->key_lower(), Eq(sorted_bucket_key_upper + 1));
+  }
+
+  // Ensure that search works normally.
+  std::vector<SectionId> expected_sections = {kDefaultSectionId};
+  for (int64_t key = max_num_data_before_split; key >= 0; key--) {
+    ASSERT_THAT(data, Contains(Key(key)));
+    DocumentId expected_document_id = data[key];
+    EXPECT_THAT(Query(storage.get(), /*key_lower=*/key, /*key_upper=*/key),
+                IsOkAndHolds(ElementsAre(EqualsDocHitInfo(expected_document_id,
+                                                          expected_sections))));
+  }
+}
+
+TEST_F(IntegerIndexStorageTest, SplitBucketsTriggerSortBuckets) {
+  ICING_ASSERT_OK_AND_ASSIGN(
+      std::unique_ptr<IntegerIndexStorage> storage,
+      IntegerIndexStorage::Create(filesystem_, working_path_, Options(),
+                                  serializer_.get()));
+
+  uint32_t block_size = FlashIndexStorage::SelectBlockSize();
+  uint32_t max_posting_list_bytes = IndexBlock::CalculateMaxPostingListBytes(
+      block_size, serializer_->GetDataTypeBytes());
+  uint32_t max_num_data_before_split =
+      max_posting_list_bytes / serializer_->GetDataTypeBytes();
+
+  // Add IntegerIndexStorage::kUnsortedBucketsLengthThreshold keys. For each
+  // key, add max_num_data_before_split + 1 data. Then we will get:
+  // - Bucket splitting will create kUnsortedBucketsLengthThreshold + 1 unsorted
+  //   buckets [[50, 50], [49, 49], ..., [1, 1], [51, INT64_MAX]].
+  // - Since there are kUnsortedBucketsLengthThreshold + 1 unsorted buckets, we
+  //   should sort and merge buckets.
+  std::unordered_map<int64_t, std::vector<DocumentId>> data;
+  int64_t key = IntegerIndexStorage::kUnsortedBucketsLengthThreshold;
+  DocumentId document_id = 0;
+  for (int i = 0; i < IntegerIndexStorage::kUnsortedBucketsLengthThreshold;
+       ++i) {
+    for (int j = 0; j < max_num_data_before_split + 1; ++j) {
+      data[key].push_back(document_id);
+      ICING_ASSERT_OK(
+          storage->AddKeys(document_id, kDefaultSectionId, /*new_keys=*/{key}));
+      ++document_id;
+    }
+    --key;
+  }
+  ICING_ASSERT_OK(storage->PersistToDisk());
+
+  // Manually check sorted and unsorted buckets.
+  {
+    // Check unsorted buckets.
+    const std::string unsorted_buckets_file_path = absl_ports::StrCat(
+        working_path_, "/", IntegerIndexStorage::kFilePrefix, ".u");
+    ICING_ASSERT_OK_AND_ASSIGN(
+        std::unique_ptr<FileBackedVector<Bucket>> unsorted_buckets,
+        FileBackedVector<Bucket>::Create(
+            filesystem_, unsorted_buckets_file_path,
+            MemoryMappedFile::Strategy::READ_WRITE_AUTO_SYNC));
+    EXPECT_THAT(unsorted_buckets->num_elements(), Eq(0));
+
+    // Check sorted buckets.
+    const std::string sorted_buckets_file_path = absl_ports::StrCat(
+        working_path_, "/", IntegerIndexStorage::kFilePrefix, ".s");
+    ICING_ASSERT_OK_AND_ASSIGN(
+        std::unique_ptr<FileBackedVector<Bucket>> sorted_buckets,
+        FileBackedVector<Bucket>::Create(
+            filesystem_, sorted_buckets_file_path,
+            MemoryMappedFile::Strategy::READ_WRITE_AUTO_SYNC));
+    EXPECT_THAT(sorted_buckets->num_elements(), Gt(1));
+  }
+
+  // Ensure that search works normally.
+  for (key = 1; key <= IntegerIndexStorage::kUnsortedBucketsLengthThreshold;
+       ++key) {
+    ASSERT_THAT(data, Contains(Key(key)));
+
+    std::vector<DocHitInfo> expected_doc_hit_infos;
+    for (DocumentId doc_id : data[key]) {
+      expected_doc_hit_infos.push_back(DocHitInfo(
+          doc_id, /*hit_section_ids_mask=*/UINT64_C(1) << kDefaultSectionId));
+    }
+    EXPECT_THAT(Query(storage.get(), /*key_lower=*/key, /*key_upper=*/key),
+                IsOkAndHolds(ElementsAreArray(expected_doc_hit_infos.rbegin(),
+                                              expected_doc_hit_infos.rend())));
+  }
+}
+
 TEST_F(IntegerIndexStorageTest, TransferIndex) {
   // We use predefined custom buckets to initialize new integer index storage
   // and create some test keys accordingly.
diff --git a/icing/index/numeric/integer-index.cc b/icing/index/numeric/integer-index.cc
index a2d40f1..2f876e4 100644
--- a/icing/index/numeric/integer-index.cc
+++ b/icing/index/numeric/integer-index.cc
@@ -14,10 +14,12 @@
 
 #include "icing/index/numeric/integer-index.h"
 
+#include <algorithm>
 #include <cstdint>
 #include <memory>
 #include <string>
 #include <string_view>
+#include <utility>
 #include <vector>
 
 #include "icing/text_classifier/lib3/utils/base/status.h"
@@ -27,6 +29,7 @@
 #include "icing/file/destructible-directory.h"
 #include "icing/file/filesystem.h"
 #include "icing/file/memory-mapped-file.h"
+#include "icing/index/iterator/doc-hit-info-iterator-section-restrict.h"
 #include "icing/index/numeric/doc-hit-info-iterator-numeric.h"
 #include "icing/index/numeric/integer-index-storage.h"
 #include "icing/index/numeric/posting-list-integer-index-serializer.h"
@@ -50,6 +53,17 @@ std::string GetMetadataFilePath(std::string_view working_path) {
   return absl_ports::StrCat(working_path, "/", GetMetadataFileName());
 }
 
+constexpr std::string_view kWildcardPropertyIndexFileName =
+    "wildcard_property_index";
+
+constexpr std::string_view kWildcardPropertyStorageFileName =
+    "wildcard_property_storage";
+
+std::string GetWildcardPropertyStorageFilePath(std::string_view working_path) {
+  return absl_ports::StrCat(working_path, "/",
+                            kWildcardPropertyStorageFileName);
+}
+
 // Helper function to get the sub working (directory) path of
 // IntegerIndexStorage according to the given working directory and property
 // path.
@@ -64,8 +78,9 @@ libtextclassifier3::StatusOr<std::vector<std::string>>
 GetAllExistingPropertyPaths(const Filesystem& filesystem,
                             const std::string& working_path) {
   std::vector<std::string> property_paths;
-  if (!filesystem.ListDirectory(working_path.c_str(),
-                                /*exclude=*/{GetMetadataFileName()},
+  std::unordered_set<std::string> excludes = {
+      GetMetadataFileName(), std::string(kWildcardPropertyStorageFileName)};
+  if (!filesystem.ListDirectory(working_path.c_str(), excludes,
                                 /*recursive=*/false, &property_paths)) {
     return absl_ports::InternalError("Failed to list directory");
   }
@@ -81,6 +96,9 @@ GetPropertyIntegerIndexStorageMap(
 
   IntegerIndex::PropertyToStorageMapType property_to_storage_map;
   for (const std::string& property_path : property_paths) {
+    if (property_path == kWildcardPropertyIndexFileName) {
+      continue;
+    }
     std::string storage_working_path =
         GetPropertyIndexStoragePath(working_path, property_path);
     ICING_ASSIGN_OR_RETURN(
@@ -95,16 +113,61 @@ GetPropertyIntegerIndexStorageMap(
   return property_to_storage_map;
 }
 
+// RETURNS:
+//   - On success, an unordered_set representing the list of property paths
+//     stored in the WildcardPropertyStorage managed by property_storage
+//   - INTERNAL_ERROR on any failure to successfully read the underlying proto.
+libtextclassifier3::StatusOr<std::unordered_set<std::string>> CreatePropertySet(
+    const FileBackedProto<WildcardPropertyStorage>& property_storage) {
+  std::unordered_set<std::string> wildcard_properties_set;
+  auto wildcard_properties_or = property_storage.Read();
+  if (!wildcard_properties_or.ok()) {
+    if (absl_ports::IsNotFound(wildcard_properties_or.status())) {
+      return wildcard_properties_set;
+    }
+    return wildcard_properties_or.status();
+  }
+
+  const WildcardPropertyStorage* wildcard_properties =
+      wildcard_properties_or.ValueOrDie();
+  wildcard_properties_set.reserve(wildcard_properties->property_entries_size());
+  for (const std::string& property : wildcard_properties->property_entries()) {
+    wildcard_properties_set.insert(property);
+  }
+  return wildcard_properties_set;
+}
+
 }  // namespace
 
 libtextclassifier3::Status IntegerIndex::Editor::IndexAllBufferedKeys() && {
   auto iter = integer_index_.property_to_storage_map_.find(property_path_);
   IntegerIndexStorage* target_storage = nullptr;
+  // 1. Check if this property already has its own individual index.
   if (iter != integer_index_.property_to_storage_map_.end()) {
     target_storage = iter->second.get();
+    // 2. Check if this property was added to wildcard storage.
+  } else if (integer_index_.wildcard_properties_set_.find(property_path_) !=
+             integer_index_.wildcard_properties_set_.end()) {
+    target_storage = integer_index_.wildcard_index_storage_.get();
+    // 3. Check if we've reach the limit of individual property storages.
+  } else if (integer_index_.property_to_storage_map_.size() >=
+             kMaxPropertyStorages) {
+    // 3a. Create the wildcard storage if it doesn't exist.
+    if (integer_index_.wildcard_index_storage_ == nullptr) {
+      ICING_ASSIGN_OR_RETURN(
+          integer_index_.wildcard_index_storage_,
+          IntegerIndexStorage::Create(
+              integer_index_.filesystem_,
+              GetPropertyIndexStoragePath(integer_index_.working_path_,
+                                          kWildcardPropertyIndexFileName),
+              IntegerIndexStorage::Options(),
+              integer_index_.posting_list_serializer_.get()));
+    }
+    ICING_RETURN_IF_ERROR(
+        integer_index_.AddPropertyToWildcardStorage(property_path_));
+    target_storage = integer_index_.wildcard_index_storage_.get();
+    // 4. Create a new individual storage for this new property.
   } else {
-    // A new property path. Create a new storage instance and insert into the
-    // map.
     ICING_ASSIGN_OR_RETURN(
         std::unique_ptr<IntegerIndexStorage> new_storage,
         IntegerIndexStorage::Create(
@@ -144,15 +207,45 @@ IntegerIndex::~IntegerIndex() {
 
 libtextclassifier3::StatusOr<std::unique_ptr<DocHitInfoIterator>>
 IntegerIndex::GetIterator(std::string_view property_path, int64_t key_lower,
-                          int64_t key_upper) const {
-  auto iter = property_to_storage_map_.find(std::string(property_path));
-  if (iter == property_to_storage_map_.end()) {
-    // Return an empty iterator.
-    return std::make_unique<DocHitInfoIteratorNumeric<int64_t>>(
-        /*numeric_index_iter=*/nullptr);
+                          int64_t key_upper,
+                          const DocumentStore& document_store,
+                          const SchemaStore& schema_store) const {
+  std::string property_path_str(property_path);
+  auto iter = property_to_storage_map_.find(property_path_str);
+  if (iter != property_to_storage_map_.end()) {
+    return iter->second->GetIterator(key_lower, key_upper);
+  }
+
+  if (wildcard_properties_set_.find(property_path_str) !=
+      wildcard_properties_set_.end()) {
+    ICING_ASSIGN_OR_RETURN(
+        std::unique_ptr<DocHitInfoIterator> delegate,
+        wildcard_index_storage_->GetIterator(key_lower, key_upper));
+    std::set<std::string> property_paths = {std::move(property_path_str)};
+    return std::make_unique<DocHitInfoIteratorSectionRestrict>(
+        std::move(delegate), &document_store, &schema_store,
+        std::move(property_paths));
+  }
+
+  // Return an empty iterator.
+  return std::make_unique<DocHitInfoIteratorNumeric<int64_t>>(
+      /*numeric_index_iter=*/nullptr);
+}
+
+libtextclassifier3::Status IntegerIndex::AddPropertyToWildcardStorage(
+    const std::string& property_path) {
+  WildcardPropertyStorage wildcard_properties;
+  wildcard_properties.mutable_property_entries()->Reserve(
+      wildcard_properties_set_.size());
+  for (const std::string& property_path : wildcard_properties_set_) {
+    wildcard_properties.add_property_entries(property_path);
   }
+  ICING_RETURN_IF_ERROR(wildcard_property_storage_->Write(
+      std::make_unique<WildcardPropertyStorage>(
+          std::move(wildcard_properties))));
 
-  return iter->second->GetIterator(key_lower, key_upper);
+  wildcard_properties_set_.insert(property_path);
+  return libtextclassifier3::Status::OK;
 }
 
 libtextclassifier3::Status IntegerIndex::Optimize(
@@ -183,6 +276,8 @@ libtextclassifier3::Status IntegerIndex::Optimize(
   // Destruct current storage instances to safely swap directories.
   metadata_mmapped_file_.reset();
   property_to_storage_map_.clear();
+  wildcard_index_storage_.reset();
+  wildcard_property_storage_.reset();
   if (!filesystem_.SwapFiles(temp_working_path_ddir.dir().c_str(),
                              working_path_.c_str())) {
     return absl_ports::InternalError(
@@ -190,9 +285,10 @@ libtextclassifier3::Status IntegerIndex::Optimize(
   }
 
   // Reinitialize the integer index.
+  std::string metadata_file_path = GetMetadataFilePath(working_path_);
   ICING_ASSIGN_OR_RETURN(
       MemoryMappedFile metadata_mmapped_file,
-      MemoryMappedFile::Create(filesystem_, GetMetadataFilePath(working_path_),
+      MemoryMappedFile::Create(filesystem_, metadata_file_path,
                                MemoryMappedFile::Strategy::READ_WRITE_AUTO_SYNC,
                                /*max_file_size=*/kMetadataFileSize,
                                /*pre_mapping_file_offset=*/0,
@@ -200,6 +296,25 @@ libtextclassifier3::Status IntegerIndex::Optimize(
   metadata_mmapped_file_ =
       std::make_unique<MemoryMappedFile>(std::move(metadata_mmapped_file));
 
+  // Recreate all of the data structures tracking the wildcard storage.
+  std::string wildcard_property_path =
+      GetWildcardPropertyStorageFilePath(working_path_);
+  wildcard_property_storage_ =
+      std::make_unique<FileBackedProto<WildcardPropertyStorage>>(
+          filesystem_, wildcard_property_path);
+
+  ICING_ASSIGN_OR_RETURN(wildcard_properties_set_,
+                         CreatePropertySet(*wildcard_property_storage_));
+  if (!wildcard_properties_set_.empty()) {
+    ICING_ASSIGN_OR_RETURN(
+        wildcard_index_storage_,
+        IntegerIndexStorage::Create(
+            filesystem_,
+            GetPropertyIndexStoragePath(working_path_,
+                                        kWildcardPropertyIndexFileName),
+            IntegerIndexStorage::Options(), posting_list_serializer_.get()));
+  }
+
   // Initialize all existing integer index storages.
   ICING_ASSIGN_OR_RETURN(
       property_to_storage_map_,
@@ -212,6 +327,7 @@ libtextclassifier3::Status IntegerIndex::Optimize(
 libtextclassifier3::Status IntegerIndex::Clear() {
   // Step 1: clear property_to_storage_map_.
   property_to_storage_map_.clear();
+  wildcard_index_storage_.reset();
 
   // Step 2: delete all IntegerIndexStorages. It is safe because there is no
   //         active IntegerIndexStorage after clearing the map.
@@ -224,6 +340,15 @@ libtextclassifier3::Status IntegerIndex::Clear() {
         GetPropertyIndexStoragePath(working_path_, property_path)));
   }
 
+  // Step 3: Delete the wildcard property storage
+  std::string wildcard_property_path =
+      GetWildcardPropertyStorageFilePath(working_path_);
+  if (filesystem_.FileExists(wildcard_property_path.c_str()) ||
+      !filesystem_.DeleteFile(wildcard_property_path.c_str())) {
+    return absl_ports::InternalError(absl_ports::StrCat(
+        "Unable to delete file at path ", wildcard_property_path));
+  }
+
   info().last_added_document_id = kInvalidDocumentId;
   return libtextclassifier3::Status::OK;
 }
@@ -249,12 +374,20 @@ IntegerIndex::InitializeNewFiles(const Filesystem& filesystem,
   ICING_RETURN_IF_ERROR(metadata_mmapped_file.GrowAndRemapIfNecessary(
       /*file_offset=*/0, /*mmap_size=*/kMetadataFileSize));
 
+  std::string wildcard_property_path =
+      GetWildcardPropertyStorageFilePath(working_path);
+  auto wildcard_property_storage =
+      std::make_unique<FileBackedProto<WildcardPropertyStorage>>(
+          filesystem, wildcard_property_path);
+
   // Create instance.
   auto new_integer_index = std::unique_ptr<IntegerIndex>(new IntegerIndex(
       filesystem, std::move(working_path),
       std::make_unique<PostingListIntegerIndexSerializer>(),
       std::make_unique<MemoryMappedFile>(std::move(metadata_mmapped_file)),
-      /*property_to_storage_map=*/{}));
+      /*property_to_storage_map=*/{}, std::move(wildcard_property_storage),
+      /*wildcard_properties_set=*/{}, /*wildcard_index_storage=*/nullptr));
+
   // Initialize info content by writing mapped memory directly.
   Info& info_ref = new_integer_index->info();
   info_ref.magic = Info::kMagic;
@@ -287,11 +420,33 @@ IntegerIndex::InitializeExistingFiles(const Filesystem& filesystem,
       GetPropertyIntegerIndexStorageMap(filesystem, working_path,
                                         posting_list_serializer.get()));
 
+  std::string wildcard_property_path =
+      GetWildcardPropertyStorageFilePath(working_path);
+  auto wildcard_property_storage =
+      std::make_unique<FileBackedProto<WildcardPropertyStorage>>(
+          filesystem, wildcard_property_path);
+
+  ICING_ASSIGN_OR_RETURN(
+      std::unordered_set<std::string> wildcard_properties_set,
+      CreatePropertySet(*wildcard_property_storage));
+
+  std::unique_ptr<IntegerIndexStorage> wildcard_index_storage;
+  if (!wildcard_properties_set.empty()) {
+    ICING_ASSIGN_OR_RETURN(
+        wildcard_index_storage,
+        IntegerIndexStorage::Create(
+            filesystem,
+            GetPropertyIndexStoragePath(working_path,
+                                        kWildcardPropertyIndexFileName),
+            IntegerIndexStorage::Options(), posting_list_serializer.get()));
+  }
+
   // Create instance.
   auto integer_index = std::unique_ptr<IntegerIndex>(new IntegerIndex(
       filesystem, std::move(working_path), std::move(posting_list_serializer),
       std::make_unique<MemoryMappedFile>(std::move(metadata_mmapped_file)),
-      std::move(property_to_storage_map)));
+      std::move(property_to_storage_map), std::move(wildcard_property_storage),
+      std::move(wildcard_properties_set), std::move(wildcard_index_storage)));
   // Initialize existing PersistentStorage. Checksums will be validated.
   ICING_RETURN_IF_ERROR(integer_index->InitializeExistingStorage());
 
@@ -303,31 +458,78 @@ IntegerIndex::InitializeExistingFiles(const Filesystem& filesystem,
   return integer_index;
 }
 
-libtextclassifier3::Status IntegerIndex::TransferIndex(
+libtextclassifier3::StatusOr<std::unique_ptr<IntegerIndexStorage>>
+IntegerIndex::TransferIntegerIndexStorage(
     const std::vector<DocumentId>& document_id_old_to_new,
+    const IntegerIndexStorage* old_storage, const std::string& property_path,
     IntegerIndex* new_integer_index) const {
-  for (const auto& [property_path, old_storage] : property_to_storage_map_) {
-    std::string new_storage_working_path = GetPropertyIndexStoragePath(
-        new_integer_index->working_path_, property_path);
-    ICING_ASSIGN_OR_RETURN(
-        std::unique_ptr<IntegerIndexStorage> new_storage,
-        IntegerIndexStorage::Create(
-            new_integer_index->filesystem_, new_storage_working_path,
-            IntegerIndexStorage::Options(),
-            new_integer_index->posting_list_serializer_.get()));
+  std::string new_storage_working_path = GetPropertyIndexStoragePath(
+      new_integer_index->working_path_, property_path);
+  ICING_ASSIGN_OR_RETURN(
+      std::unique_ptr<IntegerIndexStorage> new_storage,
+      IntegerIndexStorage::Create(
+          new_integer_index->filesystem_, new_storage_working_path,
+          IntegerIndexStorage::Options(),
+          new_integer_index->posting_list_serializer_.get()));
+
+  ICING_RETURN_IF_ERROR(
+      old_storage->TransferIndex(document_id_old_to_new, new_storage.get()));
 
+  if (new_storage->num_data() == 0) {
+    new_storage.reset();
     ICING_RETURN_IF_ERROR(
-        old_storage->TransferIndex(document_id_old_to_new, new_storage.get()));
+        IntegerIndexStorage::Discard(filesystem_, new_storage_working_path));
+  }
+  return new_storage;
+}
+
+libtextclassifier3::Status IntegerIndex::TransferWildcardStorage(
+    IntegerIndex* new_integer_index) const {
+  auto property_storage = std::make_unique<WildcardPropertyStorage>();
+  property_storage->mutable_property_entries()->Reserve(
+      wildcard_properties_set_.size());
+  for (const std::string& property : wildcard_properties_set_) {
+    property_storage->add_property_entries(property);
+  }
+
+  ICING_RETURN_IF_ERROR(new_integer_index->wildcard_property_storage_->Write(
+      std::move(property_storage)));
+  new_integer_index->wildcard_properties_set_ = wildcard_properties_set_;
+  return libtextclassifier3::Status::OK;
+}
 
-    if (new_storage->num_data() == 0) {
-      new_storage.reset();
-      ICING_RETURN_IF_ERROR(
-          IntegerIndexStorage::Discard(filesystem_, new_storage_working_path));
-    } else {
+libtextclassifier3::Status IntegerIndex::TransferIndex(
+    const std::vector<DocumentId>& document_id_old_to_new,
+    IntegerIndex* new_integer_index) const {
+  // Transfer over the integer index storages
+  std::unique_ptr<IntegerIndexStorage> new_storage;
+  for (const auto& [property_path, old_storage] : property_to_storage_map_) {
+    ICING_ASSIGN_OR_RETURN(
+        new_storage,
+        TransferIntegerIndexStorage(document_id_old_to_new, old_storage.get(),
+                                    property_path, new_integer_index));
+    if (new_storage != nullptr) {
       new_integer_index->property_to_storage_map_.insert(
-          std::make_pair(property_path, std::move(new_storage)));
+          {property_path, std::move(new_storage)});
     }
   }
+  if (wildcard_index_storage_ != nullptr) {
+    ICING_ASSIGN_OR_RETURN(
+        new_storage,
+        TransferIntegerIndexStorage(
+            document_id_old_to_new, wildcard_index_storage_.get(),
+            std::string(kWildcardPropertyIndexFileName), new_integer_index));
+    if (new_storage != nullptr) {
+      new_integer_index->wildcard_index_storage_ = std::move(new_storage);
+
+      // The only time we need to copy over the list of properties using
+      // wildcard storage is if wildcard_index_storage and new_storage are both
+      // non-null. Otherwise, the new wildcard index storage won't have any
+      // data.
+      ICING_RETURN_IF_ERROR(TransferWildcardStorage(new_integer_index));
+    }
+  }
+
   return libtextclassifier3::Status::OK;
 }
 
@@ -335,6 +537,11 @@ libtextclassifier3::Status IntegerIndex::PersistStoragesToDisk() {
   for (auto& [_, storage] : property_to_storage_map_) {
     ICING_RETURN_IF_ERROR(storage->PersistToDisk());
   }
+  // No need to persist wildcard_properties_storage_. All calls to
+  // FileBackedProto::Write are fully written through at the time of the call.
+  if (wildcard_index_storage_) {
+    ICING_RETURN_IF_ERROR(wildcard_index_storage_->PersistToDisk());
+  }
   return libtextclassifier3::Status::OK;
 }
 
@@ -350,8 +557,8 @@ libtextclassifier3::StatusOr<Crc32> IntegerIndex::ComputeInfoChecksum() {
 }
 
 libtextclassifier3::StatusOr<Crc32> IntegerIndex::ComputeStoragesChecksum() {
-  // XOR all crcs of all storages. Since XOR is commutative and associative, the
-  // order doesn't matter.
+  // XOR all crcs of all storages. Since XOR is commutative and associative,
+  // the order doesn't matter.
   uint32_t storages_checksum = 0;
   for (auto& [property_path, storage] : property_to_storage_map_) {
     ICING_ASSIGN_OR_RETURN(Crc32 storage_crc, storage->UpdateChecksums());
@@ -359,6 +566,17 @@ libtextclassifier3::StatusOr<Crc32> IntegerIndex::ComputeStoragesChecksum() {
 
     storages_checksum ^= storage_crc.Get();
   }
+
+  if (wildcard_index_storage_ != nullptr) {
+    ICING_ASSIGN_OR_RETURN(Crc32 storage_crc,
+                           wildcard_index_storage_->UpdateChecksums());
+    storages_checksum ^= storage_crc.Get();
+  }
+
+  ICING_ASSIGN_OR_RETURN(Crc32 wildcard_properties_crc,
+                         wildcard_property_storage_->ComputeChecksum());
+  storages_checksum ^= wildcard_properties_crc.Get();
+
   return Crc32(storages_checksum);
 }
 
diff --git a/icing/index/numeric/integer-index.h b/icing/index/numeric/integer-index.h
index 050a143..303bb41 100644
--- a/icing/index/numeric/integer-index.h
+++ b/icing/index/numeric/integer-index.h
@@ -23,12 +23,16 @@
 
 #include "icing/text_classifier/lib3/utils/base/status.h"
 #include "icing/text_classifier/lib3/utils/base/statusor.h"
+#include "icing/file/file-backed-proto.h"
 #include "icing/file/filesystem.h"
 #include "icing/file/memory-mapped-file.h"
 #include "icing/index/numeric/integer-index-storage.h"
 #include "icing/index/numeric/numeric-index.h"
 #include "icing/index/numeric/posting-list-integer-index-serializer.h"
+#include "icing/index/numeric/wildcard-property-storage.pb.h"
+#include "icing/schema/schema-store.h"
 #include "icing/store/document-id.h"
+#include "icing/store/document-store.h"
 #include "icing/util/crc32.h"
 
 namespace icing {
@@ -46,6 +50,11 @@ class IntegerIndex : public NumericIndex<int64_t> {
   using PropertyToStorageMapType =
       std::unordered_map<std::string, std::unique_ptr<IntegerIndexStorage>>;
 
+  // Maximum number of individual property storages that this index will allow
+  // before falling back to placing hits for any new properties into the
+  // 'wildcard' storage.
+  static constexpr int kMaxPropertyStorages = 32;
+
   struct Info {
     static constexpr int32_t kMagic = 0x238a3dcb;
 
@@ -125,8 +134,9 @@ class IntegerIndex : public NumericIndex<int64_t> {
   //   - NOT_FOUND_ERROR if the given property_path doesn't exist
   //   - Any IntegerIndexStorage errors
   libtextclassifier3::StatusOr<std::unique_ptr<DocHitInfoIterator>> GetIterator(
-      std::string_view property_path, int64_t key_lower,
-      int64_t key_upper) const override;
+      std::string_view property_path, int64_t key_lower, int64_t key_upper,
+      const DocumentStore& document_store,
+      const SchemaStore& schema_store) const override;
 
   // Reduces internal file sizes by reclaiming space and ids of deleted
   // documents. Integer index will convert all data (hits) to the new document
@@ -165,6 +175,11 @@ class IntegerIndex : public NumericIndex<int64_t> {
     }
   }
 
+  int num_property_indices() const override {
+    return property_to_storage_map_.size() +
+           ((wildcard_index_storage_ == nullptr) ? 0 : 1);
+  }
+
  private:
   class Editor : public NumericIndex<int64_t>::Editor {
    public:
@@ -191,17 +206,24 @@ class IntegerIndex : public NumericIndex<int64_t> {
     IntegerIndex& integer_index_;  // Does not own.
   };
 
-  explicit IntegerIndex(const Filesystem& filesystem,
-                        std::string&& working_path,
-                        std::unique_ptr<PostingListIntegerIndexSerializer>
-                            posting_list_serializer,
-                        std::unique_ptr<MemoryMappedFile> metadata_mmapped_file,
-                        PropertyToStorageMapType&& property_to_storage_map)
+  explicit IntegerIndex(
+      const Filesystem& filesystem, std::string&& working_path,
+      std::unique_ptr<PostingListIntegerIndexSerializer>
+          posting_list_serializer,
+      std::unique_ptr<MemoryMappedFile> metadata_mmapped_file,
+      PropertyToStorageMapType&& property_to_storage_map,
+      std::unique_ptr<FileBackedProto<WildcardPropertyStorage>>
+          wildcard_property_storage,
+      std::unordered_set<std::string> wildcard_properties_set,
+      std::unique_ptr<icing::lib::IntegerIndexStorage> wildcard_index_storage)
       : NumericIndex<int64_t>(filesystem, std::move(working_path),
                               kWorkingPathType),
         posting_list_serializer_(std::move(posting_list_serializer)),
         metadata_mmapped_file_(std::move(metadata_mmapped_file)),
-        property_to_storage_map_(std::move(property_to_storage_map)) {}
+        property_to_storage_map_(std::move(property_to_storage_map)),
+        wildcard_property_storage_(std::move(wildcard_property_storage)),
+        wildcard_properties_set_(std::move(wildcard_properties_set)),
+        wildcard_index_storage_(std::move(wildcard_index_storage)) {}
 
   static libtextclassifier3::StatusOr<std::unique_ptr<IntegerIndex>>
   InitializeNewFiles(const Filesystem& filesystem, std::string&& working_path);
@@ -210,6 +232,17 @@ class IntegerIndex : public NumericIndex<int64_t> {
   InitializeExistingFiles(const Filesystem& filesystem,
                           std::string&& working_path);
 
+  // Adds the property path to the list of properties using wildcard storage.
+  // This will both update the in-memory list (wildcard_properties_set_) and
+  // the persistent list (wilcard_property_storage_).
+  //
+  // RETURNS:
+  //   - OK on success
+  //   - INTERNAL_ERROR if unable to successfully persist updated properties
+  //     list in wildcard_property_storage_.
+  libtextclassifier3::Status AddPropertyToWildcardStorage(
+      const std::string& property_path);
+
   // Transfers integer index data from the current integer index to
   // new_integer_index.
   //
@@ -222,6 +255,29 @@ class IntegerIndex : public NumericIndex<int64_t> {
       const std::vector<DocumentId>& document_id_old_to_new,
       IntegerIndex* new_integer_index) const;
 
+  // Transfers integer index data from old_storage to new_integer_index.
+  //
+  // Returns:
+  //   - OK on success
+  //   - INTERNAL_ERROR on I/O error. This could potentially leave the storages
+  //     in an invalid state and the caller should handle it properly (e.g.
+  //     discard and rebuild)
+  libtextclassifier3::StatusOr<std::unique_ptr<IntegerIndexStorage>>
+  TransferIntegerIndexStorage(
+      const std::vector<DocumentId>& document_id_old_to_new,
+      const IntegerIndexStorage* old_storage, const std::string& property_path,
+      IntegerIndex* new_integer_index) const;
+
+  // Transfers the persistent and in-memory list of properties using the
+  // wildcard storage from old_storage to new_integer_index.
+  //
+  // RETURNS:
+  //   - OK on success
+  //   - INTERNAL_ERROR if unable to successfully persist updated properties
+  //     list in new_integer_index.
+  libtextclassifier3::Status TransferWildcardStorage(
+      IntegerIndex* new_integer_index) const;
+
   // Flushes contents of all storages to underlying files.
   //
   // Returns:
@@ -277,6 +333,19 @@ class IntegerIndex : public NumericIndex<int64_t> {
 
   // Property path to integer index storage map.
   PropertyToStorageMapType property_to_storage_map_;
+
+  // Persistent list of properties that have added content to
+  // wildcard_index_storage_.
+  std::unique_ptr<FileBackedProto<WildcardPropertyStorage>>
+      wildcard_property_storage_;
+
+  // In-memory list of properties that have added content to
+  // wildcard_index_storage_.
+  std::unordered_set<std::string> wildcard_properties_set_;
+
+  // The index storage that is used once we have already created
+  // kMaxPropertyStorages in property_to_storage_map.
+  std::unique_ptr<icing::lib::IntegerIndexStorage> wildcard_index_storage_;
 };
 
 }  // namespace lib
diff --git a/icing/index/numeric/integer-index_test.cc b/icing/index/numeric/integer-index_test.cc
index c6cf855..c4dacb8 100644
--- a/icing/index/numeric/integer-index_test.cc
+++ b/icing/index/numeric/integer-index_test.cc
@@ -25,6 +25,7 @@
 #include "icing/text_classifier/lib3/utils/base/statusor.h"
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
+#include "icing/document-builder.h"
 #include "icing/file/filesystem.h"
 #include "icing/index/hit/doc-hit-info.h"
 #include "icing/index/iterator/doc-hit-info-iterator.h"
@@ -32,6 +33,9 @@
 #include "icing/index/numeric/integer-index-storage.h"
 #include "icing/index/numeric/numeric-index.h"
 #include "icing/index/numeric/posting-list-integer-index-serializer.h"
+#include "icing/proto/document.pb.h"
+#include "icing/proto/schema.pb.h"
+#include "icing/schema-builder.h"
 #include "icing/schema/section.h"
 #include "icing/store/document-id.h"
 #include "icing/testing/common-matchers.h"
@@ -68,9 +72,25 @@ class NumericIndexIntegerTest : public ::testing::Test {
                 IsTrue());
 
     working_path_ = base_dir_ + "/numeric_index_integer_test";
+    std::string schema_dir = base_dir_ + "/schema_test";
+
+    ASSERT_TRUE(filesystem_.CreateDirectoryRecursively(schema_dir.c_str()));
+    ICING_ASSERT_OK_AND_ASSIGN(
+        schema_store_, SchemaStore::Create(&filesystem_, schema_dir, &clock_));
+
+    std::string document_store_dir = base_dir_ + "/doc_store_test";
+    ASSERT_TRUE(
+        filesystem_.CreateDirectoryRecursively(document_store_dir.c_str()));
+    ICING_ASSERT_OK_AND_ASSIGN(
+        DocumentStore::CreateResult doc_store_create_result,
+        DocumentStore::Create(&filesystem_, document_store_dir, &clock_,
+                              schema_store_.get()));
+    doc_store_ = std::move(doc_store_create_result.document_store);
   }
 
   void TearDown() override {
+    doc_store_.reset();
+    schema_store_.reset();
     filesystem_.DeleteDirectoryRecursively(base_dir_.c_str());
   }
 
@@ -92,9 +112,67 @@ class NumericIndexIntegerTest : public ::testing::Test {
     return IntegerIndex::Create(filesystem_, working_path_);
   }
 
+  template <typename NotIntegerIndexType>
+  bool is_integer_index() const {
+    return false;
+  }
+
+  template <>
+  bool is_integer_index<IntegerIndex>() const {
+    return true;
+  }
+
+  libtextclassifier3::StatusOr<std::vector<DocumentId>> CompactDocStore() {
+    std::string document_store_dir = base_dir_ + "/doc_store_test";
+    std::string document_store_compact_dir =
+        base_dir_ + "/doc_store_compact_test";
+    if (!filesystem_.CreateDirectoryRecursively(
+            document_store_compact_dir.c_str())) {
+      return absl_ports::InternalError("Unable to create compact directory");
+    }
+    ICING_ASSIGN_OR_RETURN(
+        std::vector<DocumentId> docid_map,
+        doc_store_->OptimizeInto(document_store_compact_dir, nullptr));
+
+    doc_store_.reset();
+    if (!filesystem_.SwapFiles(document_store_dir.c_str(),
+                               document_store_compact_dir.c_str())) {
+      return absl_ports::InternalError("Unable to swap directories.");
+    }
+    if (!filesystem_.DeleteDirectoryRecursively(
+            document_store_compact_dir.c_str())) {
+      return absl_ports::InternalError("Unable to delete compact directory");
+    }
+
+    ICING_ASSIGN_OR_RETURN(
+        DocumentStore::CreateResult doc_store_create_result,
+        DocumentStore::Create(&filesystem_, document_store_dir, &clock_,
+                              schema_store_.get()));
+    doc_store_ = std::move(doc_store_create_result.document_store);
+    return docid_map;
+  }
+
+  libtextclassifier3::StatusOr<std::vector<DocHitInfo>> Query(
+      const NumericIndex<int64_t>* integer_index,
+      std::string_view property_path, int64_t key_lower, int64_t key_upper) {
+    ICING_ASSIGN_OR_RETURN(
+        std::unique_ptr<DocHitInfoIterator> iter,
+        integer_index->GetIterator(property_path, key_lower, key_upper,
+                                   *doc_store_, *schema_store_));
+
+    std::vector<DocHitInfo> result;
+    while (iter->Advance().ok()) {
+      result.push_back(iter->doc_hit_info());
+    }
+    return result;
+  }
+
   Filesystem filesystem_;
   std::string base_dir_;
   std::string working_path_;
+  std::unique_ptr<SchemaStore> schema_store_;
+  std::unique_ptr<DocumentStore> doc_store_;
+  Clock clock_;
 };
 
 void Index(NumericIndex<int64_t>* integer_index, std::string_view property_path,
@@ -109,20 +187,6 @@ void Index(NumericIndex<int64_t>* integer_index, std::string_view property_path,
   ICING_EXPECT_OK(std::move(*editor).IndexAllBufferedKeys());
 }
 
-libtextclassifier3::StatusOr<std::vector<DocHitInfo>> Query(
-    const NumericIndex<int64_t>* integer_index, std::string_view property_path,
-    int64_t key_lower, int64_t key_upper) {
-  ICING_ASSIGN_OR_RETURN(
-      std::unique_ptr<DocHitInfoIterator> iter,
-      integer_index->GetIterator(property_path, key_lower, key_upper));
-
-  std::vector<DocHitInfo> result;
-  while (iter->Advance().ok()) {
-    result.push_back(iter->doc_hit_info());
-  }
-  return result;
-}
-
 using TestTypes = ::testing::Types<DummyNumericIndex<int64_t>, IntegerIndex>;
 TYPED_TEST_SUITE(NumericIndexIntegerTest, TestTypes);
 
@@ -180,8 +244,8 @@ TYPED_TEST(NumericIndexIntegerTest, SingleKeyExactQuery) {
 
   int64_t query_key = 2;
   std::vector<SectionId> expected_sections = {kDefaultSectionId};
-  EXPECT_THAT(Query(integer_index.get(), kDefaultTestPropertyPath,
-                    /*key_lower=*/query_key, /*key_upper=*/query_key),
+  EXPECT_THAT(this->Query(integer_index.get(), kDefaultTestPropertyPath,
+                          /*key_lower=*/query_key, /*key_upper=*/query_key),
               IsOkAndHolds(ElementsAre(
                   EqualsDocHitInfo(/*document_id=*/5, expected_sections),
                   EqualsDocHitInfo(/*document_id=*/2, expected_sections))));
@@ -206,8 +270,8 @@ TYPED_TEST(NumericIndexIntegerTest, SingleKeyRangeQuery) {
         kDefaultSectionId, /*keys=*/{2});
 
   std::vector<SectionId> expected_sections = {kDefaultSectionId};
-  EXPECT_THAT(Query(integer_index.get(), kDefaultTestPropertyPath,
-                    /*key_lower=*/1, /*key_upper=*/3),
+  EXPECT_THAT(this->Query(integer_index.get(), kDefaultTestPropertyPath,
+                          /*key_lower=*/1, /*key_upper=*/3),
               IsOkAndHolds(ElementsAre(
                   EqualsDocHitInfo(/*document_id=*/5, expected_sections),
                   EqualsDocHitInfo(/*document_id=*/2, expected_sections),
@@ -215,6 +279,258 @@ TYPED_TEST(NumericIndexIntegerTest, SingleKeyRangeQuery) {
                   EqualsDocHitInfo(/*document_id=*/0, expected_sections))));
 }
 
+TYPED_TEST(NumericIndexIntegerTest, WildcardStorageQuery) {
+  ICING_ASSERT_OK_AND_ASSIGN(
+      std::unique_ptr<NumericIndex<int64_t>> integer_index,
+      this->template CreateIntegerIndex<TypeParam>());
+
+  // This test sets its schema assuming that max property storages == 32.
+  ASSERT_THAT(IntegerIndex::kMaxPropertyStorages, Eq(32));
+
+  PropertyConfigProto int_property_config =
+      PropertyConfigBuilder()
+          .SetName("otherProperty1")
+          .SetCardinality(CARDINALITY_REPEATED)
+          .SetDataTypeInt64(NUMERIC_MATCH_RANGE)
+          .Build();
+  // Create a schema with two types:
+  // - TypeA has 34 properties:
+  //     'desiredProperty', 'otherProperty'*, 'undesiredProperty'
+  // - TypeB has 2 properties: 'anotherProperty', 'desiredProperty'
+  // 1. The 32 'otherProperty's will consume all of the individual storages
+  // 2. TypeA.desiredProperty and TypeB.anotherProperty will both be assigned
+  //    SectionId = 0 for their respective types.
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("TypeA")
+                       .AddProperty(int_property_config)
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty2"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty3"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty4"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty5"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty6"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty7"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty8"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty9"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty10"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty11"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty12"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty13"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty14"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty15"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty16"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty17"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty18"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty19"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty20"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty21"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty22"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty23"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty24"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty25"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty26"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty27"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty28"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty29"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty30"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty31"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty32"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("desiredProperty"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("undesiredProperty")))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("TypeB")
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("anotherProperty"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("desiredProperty")))
+          .Build();
+  ICING_ASSERT_OK(this->schema_store_->SetSchema(schema));
+
+  // Put 11 docs of "TypeA" into the document store.
+  DocumentProto doc =
+      DocumentBuilder().SetKey("ns1", "uri0").SetSchema("TypeA").Build();
+  ICING_ASSERT_OK(this->doc_store_->Put(doc));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri1").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri2").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri3").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri4").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri5").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri6").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri7").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri8").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri9").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri10").Build()));
+
+  // Put 5 docs of "TypeB" into the document store.
+  doc = DocumentBuilder(doc).SetUri("uri11").SetSchema("TypeB").Build();
+  ICING_ASSERT_OK(this->doc_store_->Put(doc));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri12").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri13").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri14").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri15").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri16").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri17").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri18").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri19").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri20").Build()));
+
+  // Ids are assigned alphabetically, so the property ids are:
+  // TypeA.desiredProperty = 0
+  // TypeA.otherPropertyN = N
+  // TypeA.undesiredProperty = 33
+  // TypeB.anotherProperty = 0
+  // TypeB.desiredProperty = 1
+  SectionId typea_desired_prop_id = 0;
+  SectionId typea_undesired_prop_id = 33;
+  SectionId typeb_another_prop_id = 0;
+  SectionId typeb_desired_prop_id = 1;
+
+  // Index numeric content for other properties to force our property into the
+  // wildcard storage.
+  std::string other_property_path = "otherProperty";
+  for (int i = 1; i <= IntegerIndex::kMaxPropertyStorages; ++i) {
+    Index(integer_index.get(),
+          absl_ports::StrCat(other_property_path, std::to_string(i)),
+          /*document_id=*/0, /*section_id=*/i, /*keys=*/{i});
+  }
+
+  // Index numeric content for TypeA.desiredProperty
+  std::string desired_property = "desiredProperty";
+  Index(integer_index.get(), desired_property, /*document_id=*/0,
+        typea_desired_prop_id, /*keys=*/{1});
+  Index(integer_index.get(), desired_property, /*document_id=*/1,
+        typea_desired_prop_id, /*keys=*/{3});
+  Index(integer_index.get(), desired_property, /*document_id=*/2,
+        typea_desired_prop_id, /*keys=*/{2});
+  Index(integer_index.get(), desired_property, /*document_id=*/3,
+        typea_desired_prop_id, /*keys=*/{0});
+  Index(integer_index.get(), desired_property, /*document_id=*/4,
+        typea_desired_prop_id, /*keys=*/{4});
+  Index(integer_index.get(), desired_property, /*document_id=*/5,
+        typea_desired_prop_id, /*keys=*/{2});
+
+  // Index the same numeric content for TypeA.undesiredProperty
+  std::string undesired_property = "undesiredProperty";
+  Index(integer_index.get(), undesired_property, /*document_id=*/6,
+        typea_undesired_prop_id, /*keys=*/{3});
+  Index(integer_index.get(), undesired_property, /*document_id=*/7,
+        typea_undesired_prop_id, /*keys=*/{2});
+  Index(integer_index.get(), undesired_property, /*document_id=*/8,
+        typea_undesired_prop_id, /*keys=*/{0});
+  Index(integer_index.get(), undesired_property, /*document_id=*/9,
+        typea_undesired_prop_id, /*keys=*/{4});
+  Index(integer_index.get(), undesired_property, /*document_id=*/10,
+        typea_undesired_prop_id, /*keys=*/{2});
+
+  // Index the same numeric content for TypeB.anotherProperty
+  std::string another_property = "anotherProperty";
+  Index(integer_index.get(), another_property, /*document_id=*/11,
+        typeb_another_prop_id, /*keys=*/{3});
+  Index(integer_index.get(), another_property, /*document_id=*/12,
+        typeb_another_prop_id, /*keys=*/{2});
+  Index(integer_index.get(), another_property, /*document_id=*/13,
+        typeb_another_prop_id, /*keys=*/{0});
+  Index(integer_index.get(), another_property, /*document_id=*/14,
+        typeb_another_prop_id, /*keys=*/{4});
+  Index(integer_index.get(), another_property, /*document_id=*/15,
+        typeb_another_prop_id, /*keys=*/{2});
+
+  // Finally, index the same numeric content for TypeB.desiredProperty
+  Index(integer_index.get(), desired_property, /*document_id=*/16,
+        typeb_desired_prop_id, /*keys=*/{3});
+  Index(integer_index.get(), desired_property, /*document_id=*/17,
+        typeb_desired_prop_id, /*keys=*/{2});
+  Index(integer_index.get(), desired_property, /*document_id=*/18,
+        typeb_desired_prop_id, /*keys=*/{0});
+  Index(integer_index.get(), desired_property, /*document_id=*/19,
+        typeb_desired_prop_id, /*keys=*/{4});
+  Index(integer_index.get(), desired_property, /*document_id=*/20,
+        typeb_desired_prop_id, /*keys=*/{2});
+
+  if (this->template is_integer_index<TypeParam>()) {
+    EXPECT_THAT(integer_index->num_property_indices(), Eq(33));
+  } else {
+    EXPECT_THAT(integer_index->num_property_indices(), Eq(35));
+  }
+
+  // Only the hits for 'desired_prop_id' should be returned.
+  std::vector<SectionId> expected_sections_typea = {typea_desired_prop_id};
+  std::vector<SectionId> expected_sections_typeb = {typeb_desired_prop_id};
+  EXPECT_THAT(
+      this->Query(integer_index.get(), desired_property,
+                  /*key_lower=*/2, /*key_upper=*/2),
+      IsOkAndHolds(ElementsAre(
+          EqualsDocHitInfo(/*document_id=*/20, expected_sections_typeb),
+          EqualsDocHitInfo(/*document_id=*/17, expected_sections_typeb),
+          EqualsDocHitInfo(/*document_id=*/5, expected_sections_typea),
+          EqualsDocHitInfo(/*document_id=*/2, expected_sections_typea))));
+
+  EXPECT_THAT(
+      this->Query(integer_index.get(), desired_property,
+                  /*key_lower=*/1, /*key_upper=*/3),
+      IsOkAndHolds(ElementsAre(
+          EqualsDocHitInfo(/*document_id=*/20, expected_sections_typeb),
+          EqualsDocHitInfo(/*document_id=*/17, expected_sections_typeb),
+          EqualsDocHitInfo(/*document_id=*/16, expected_sections_typeb),
+          EqualsDocHitInfo(/*document_id=*/5, expected_sections_typea),
+          EqualsDocHitInfo(/*document_id=*/2, expected_sections_typea),
+          EqualsDocHitInfo(/*document_id=*/1, expected_sections_typea),
+          EqualsDocHitInfo(/*document_id=*/0, expected_sections_typea))));
+}
+
 TYPED_TEST(NumericIndexIntegerTest, EmptyResult) {
   ICING_ASSERT_OK_AND_ASSIGN(
       std::unique_ptr<NumericIndex<int64_t>> integer_index,
@@ -233,11 +549,11 @@ TYPED_TEST(NumericIndexIntegerTest, EmptyResult) {
   Index(integer_index.get(), kDefaultTestPropertyPath, /*document_id=*/5,
         kDefaultSectionId, /*keys=*/{2});
 
-  EXPECT_THAT(Query(integer_index.get(), kDefaultTestPropertyPath,
-                    /*key_lower=*/10, /*key_upper=*/10),
+  EXPECT_THAT(this->Query(integer_index.get(), kDefaultTestPropertyPath,
+                          /*key_lower=*/10, /*key_upper=*/10),
               IsOkAndHolds(IsEmpty()));
-  EXPECT_THAT(Query(integer_index.get(), kDefaultTestPropertyPath,
-                    /*key_lower=*/100, /*key_upper=*/200),
+  EXPECT_THAT(this->Query(integer_index.get(), kDefaultTestPropertyPath,
+                          /*key_lower=*/100, /*key_upper=*/200),
               IsOkAndHolds(IsEmpty()));
 }
 
@@ -252,8 +568,8 @@ TYPED_TEST(NumericIndexIntegerTest,
   Index(integer_index.get(), kDefaultTestPropertyPath, /*document_id=*/0,
         kDefaultSectionId, /*keys=*/{1});
 
-  EXPECT_THAT(Query(integer_index.get(), kAnotherPropertyPath,
-                    /*key_lower=*/100, /*key_upper=*/200),
+  EXPECT_THAT(this->Query(integer_index.get(), kAnotherPropertyPath,
+                          /*key_lower=*/100, /*key_upper=*/200),
               IsOkAndHolds(IsEmpty()));
 }
 
@@ -286,8 +602,8 @@ TYPED_TEST(NumericIndexIntegerTest,
         kDefaultSectionId, /*keys=*/{4, -1000});
 
   std::vector<SectionId> expected_sections = {kDefaultSectionId};
-  EXPECT_THAT(Query(integer_index.get(), kDefaultTestPropertyPath,
-                    /*key_lower=*/1, /*key_upper=*/3),
+  EXPECT_THAT(this->Query(integer_index.get(), kDefaultTestPropertyPath,
+                          /*key_lower=*/1, /*key_upper=*/3),
               IsOkAndHolds(ElementsAre(
                   EqualsDocHitInfo(/*document_id=*/6, expected_sections),
                   EqualsDocHitInfo(/*document_id=*/5, expected_sections),
@@ -326,39 +642,39 @@ TYPED_TEST(NumericIndexIntegerTest, EdgeNumericValues) {
   std::vector<SectionId> expected_sections = {kDefaultSectionId};
 
   // Negative key
-  EXPECT_THAT(Query(integer_index.get(), kDefaultTestPropertyPath,
-                    /*key_lower=*/-100, /*key_upper=*/-70),
+  EXPECT_THAT(this->Query(integer_index.get(), kDefaultTestPropertyPath,
+                          /*key_lower=*/-100, /*key_upper=*/-70),
               IsOkAndHolds(ElementsAre(
                   EqualsDocHitInfo(/*document_id=*/2, expected_sections),
                   EqualsDocHitInfo(/*document_id=*/1, expected_sections))));
 
   // INT64_MAX key
-  EXPECT_THAT(Query(integer_index.get(), kDefaultTestPropertyPath,
-                    /*key_lower=*/std::numeric_limits<int64_t>::max(),
-                    /*key_upper=*/std::numeric_limits<int64_t>::max()),
+  EXPECT_THAT(this->Query(integer_index.get(), kDefaultTestPropertyPath,
+                          /*key_lower=*/std::numeric_limits<int64_t>::max(),
+                          /*key_upper=*/std::numeric_limits<int64_t>::max()),
               IsOkAndHolds(ElementsAre(
                   EqualsDocHitInfo(/*document_id=*/7, expected_sections),
                   EqualsDocHitInfo(/*document_id=*/3, expected_sections))));
 
   // INT64_MIN key
-  EXPECT_THAT(Query(integer_index.get(), kDefaultTestPropertyPath,
-                    /*key_lower=*/std::numeric_limits<int64_t>::min(),
-                    /*key_upper=*/std::numeric_limits<int64_t>::min()),
+  EXPECT_THAT(this->Query(integer_index.get(), kDefaultTestPropertyPath,
+                          /*key_lower=*/std::numeric_limits<int64_t>::min(),
+                          /*key_upper=*/std::numeric_limits<int64_t>::min()),
               IsOkAndHolds(ElementsAre(
                   EqualsDocHitInfo(/*document_id=*/9, expected_sections),
                   EqualsDocHitInfo(/*document_id=*/4, expected_sections))));
 
   // Key = 0
-  EXPECT_THAT(Query(integer_index.get(), kDefaultTestPropertyPath,
-                    /*key_lower=*/0, /*key_upper=*/0),
+  EXPECT_THAT(this->Query(integer_index.get(), kDefaultTestPropertyPath,
+                          /*key_lower=*/0, /*key_upper=*/0),
               IsOkAndHolds(ElementsAre(
                   EqualsDocHitInfo(/*document_id=*/8, expected_sections),
                   EqualsDocHitInfo(/*document_id=*/0, expected_sections))));
 
   // All keys from INT64_MIN to INT64_MAX
-  EXPECT_THAT(Query(integer_index.get(), kDefaultTestPropertyPath,
-                    /*key_lower=*/std::numeric_limits<int64_t>::min(),
-                    /*key_upper=*/std::numeric_limits<int64_t>::max()),
+  EXPECT_THAT(this->Query(integer_index.get(), kDefaultTestPropertyPath,
+                          /*key_lower=*/std::numeric_limits<int64_t>::min(),
+                          /*key_upper=*/std::numeric_limits<int64_t>::max()),
               IsOkAndHolds(ElementsAre(
                   EqualsDocHitInfo(/*document_id=*/9, expected_sections),
                   EqualsDocHitInfo(/*document_id=*/8, expected_sections),
@@ -404,8 +720,9 @@ TYPED_TEST(NumericIndexIntegerTest,
         /*section_id=*/3, /*keys=*/{5});
 
   EXPECT_THAT(
-      Query(integer_index.get(), kDefaultTestPropertyPath, /*key_lower=*/1,
-            /*key_upper=*/3),
+      this->Query(integer_index.get(), kDefaultTestPropertyPath,
+                  /*key_lower=*/1,
+                  /*key_upper=*/3),
       IsOkAndHolds(ElementsAre(
           EqualsDocHitInfo(/*document_id=*/2, std::vector<SectionId>{4, 5}),
           EqualsDocHitInfo(/*document_id=*/1, std::vector<SectionId>{1, 2}),
@@ -433,8 +750,8 @@ TYPED_TEST(NumericIndexIntegerTest, NonRelevantPropertyShouldNotBeIncluded) {
         kDefaultSectionId, /*keys=*/{2});
 
   std::vector<SectionId> expected_sections = {kDefaultSectionId};
-  EXPECT_THAT(Query(integer_index.get(), kDefaultTestPropertyPath,
-                    /*key_lower=*/1, /*key_upper=*/3),
+  EXPECT_THAT(this->Query(integer_index.get(), kDefaultTestPropertyPath,
+                          /*key_lower=*/1, /*key_upper=*/3),
               IsOkAndHolds(ElementsAre(
                   EqualsDocHitInfo(/*document_id=*/5, expected_sections),
                   EqualsDocHitInfo(/*document_id=*/1, expected_sections),
@@ -460,8 +777,8 @@ TYPED_TEST(NumericIndexIntegerTest,
   Index(integer_index.get(), kDefaultTestPropertyPath, /*document_id=*/5,
         kDefaultSectionId, /*keys=*/{2});
 
-  EXPECT_THAT(Query(integer_index.get(), kDefaultTestPropertyPath,
-                    /*key_lower=*/3, /*key_upper=*/1),
+  EXPECT_THAT(this->Query(integer_index.get(), kDefaultTestPropertyPath,
+                          /*key_lower=*/3, /*key_upper=*/1),
               StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
 }
 
@@ -499,30 +816,30 @@ TYPED_TEST(NumericIndexIntegerTest, Optimize) {
 
   // Verify index and query API still work normally after Optimize().
   std::vector<SectionId> expected_sections = {kDefaultSectionId};
-  EXPECT_THAT(Query(integer_index.get(), kDefaultTestPropertyPath,
-                    /*key_lower=*/1, /*key_upper=*/1),
+  EXPECT_THAT(this->Query(integer_index.get(), kDefaultTestPropertyPath,
+                          /*key_lower=*/1, /*key_upper=*/1),
               IsOkAndHolds(ElementsAre(
                   EqualsDocHitInfo(/*document_id=*/0, expected_sections))));
-  EXPECT_THAT(Query(integer_index.get(), kDefaultTestPropertyPath,
-                    /*key_lower=*/3, /*key_upper=*/3),
+  EXPECT_THAT(this->Query(integer_index.get(), kDefaultTestPropertyPath,
+                          /*key_lower=*/3, /*key_upper=*/3),
               IsOkAndHolds(ElementsAre(
                   EqualsDocHitInfo(/*document_id=*/1, expected_sections))));
-  EXPECT_THAT(Query(integer_index.get(), kDefaultTestPropertyPath,
-                    /*key_lower=*/0, /*key_upper=*/0),
+  EXPECT_THAT(this->Query(integer_index.get(), kDefaultTestPropertyPath,
+                          /*key_lower=*/0, /*key_upper=*/0),
               IsOkAndHolds(IsEmpty()));
-  EXPECT_THAT(Query(integer_index.get(), kDefaultTestPropertyPath,
-                    /*key_lower=*/4, /*key_upper=*/4),
+  EXPECT_THAT(this->Query(integer_index.get(), kDefaultTestPropertyPath,
+                          /*key_lower=*/4, /*key_upper=*/4),
               IsOkAndHolds(ElementsAre(
                   EqualsDocHitInfo(/*document_id=*/2, expected_sections))));
-  EXPECT_THAT(Query(integer_index.get(), kDefaultTestPropertyPath,
-                    /*key_lower=*/2, /*key_upper=*/2),
+  EXPECT_THAT(this->Query(integer_index.get(), kDefaultTestPropertyPath,
+                          /*key_lower=*/2, /*key_upper=*/2),
               IsOkAndHolds(ElementsAre(
                   EqualsDocHitInfo(/*document_id=*/3, expected_sections))));
 
   Index(integer_index.get(), kDefaultTestPropertyPath, /*document_id=*/5,
         kDefaultSectionId, /*keys=*/{123});
-  EXPECT_THAT(Query(integer_index.get(), kDefaultTestPropertyPath,
-                    /*key_lower=*/123, /*key_upper=*/123),
+  EXPECT_THAT(this->Query(integer_index.get(), kDefaultTestPropertyPath,
+                          /*key_lower=*/123, /*key_upper=*/123),
               IsOkAndHolds(ElementsAre(
                   EqualsDocHitInfo(/*document_id=*/5, expected_sections))));
 }
@@ -581,40 +898,40 @@ TYPED_TEST(NumericIndexIntegerTest, OptimizeMultiplePropertyPaths) {
 
   // Verify index and query API still work normally after Optimize().
   // Key = 1
-  EXPECT_THAT(Query(integer_index.get(), kPropertyPath1, /*key_lower=*/1,
-                    /*key_upper=*/1),
+  EXPECT_THAT(this->Query(integer_index.get(), kPropertyPath1, /*key_lower=*/1,
+                          /*key_upper=*/1),
               IsOkAndHolds(IsEmpty()));
-  EXPECT_THAT(Query(integer_index.get(), kPropertyPath2, /*key_lower=*/1,
-                    /*key_upper=*/1),
+  EXPECT_THAT(this->Query(integer_index.get(), kPropertyPath2, /*key_lower=*/1,
+                          /*key_upper=*/1),
               IsOkAndHolds(ElementsAre(EqualsDocHitInfo(
                   /*document_id=*/0, std::vector<SectionId>{kSectionId2}))));
 
   // key = 2
-  EXPECT_THAT(Query(integer_index.get(), kPropertyPath1, /*key_lower=*/2,
-                    /*key_upper=*/2),
+  EXPECT_THAT(this->Query(integer_index.get(), kPropertyPath1, /*key_lower=*/2,
+                          /*key_upper=*/2),
               IsOkAndHolds(ElementsAre(EqualsDocHitInfo(
                   /*document_id=*/0, std::vector<SectionId>{kSectionId1}))));
-  EXPECT_THAT(Query(integer_index.get(), kPropertyPath2, /*key_lower=*/2,
-                    /*key_upper=*/2),
+  EXPECT_THAT(this->Query(integer_index.get(), kPropertyPath2, /*key_lower=*/2,
+                          /*key_upper=*/2),
               IsOkAndHolds(IsEmpty()));
 
   // key = 3
-  EXPECT_THAT(Query(integer_index.get(), kPropertyPath1, /*key_lower=*/3,
-                    /*key_upper=*/3),
+  EXPECT_THAT(this->Query(integer_index.get(), kPropertyPath1, /*key_lower=*/3,
+                          /*key_upper=*/3),
               IsOkAndHolds(ElementsAre(EqualsDocHitInfo(
                   /*document_id=*/1, std::vector<SectionId>{kSectionId1}))));
-  EXPECT_THAT(Query(integer_index.get(), kPropertyPath2, /*key_lower=*/3,
-                    /*key_upper=*/3),
+  EXPECT_THAT(this->Query(integer_index.get(), kPropertyPath2, /*key_lower=*/3,
+                          /*key_upper=*/3),
               IsOkAndHolds(ElementsAre(EqualsDocHitInfo(
                   /*document_id=*/2, std::vector<SectionId>{kSectionId2}))));
 
   // key = 4
-  EXPECT_THAT(Query(integer_index.get(), kPropertyPath1, /*key_lower=*/4,
-                    /*key_upper=*/4),
+  EXPECT_THAT(this->Query(integer_index.get(), kPropertyPath1, /*key_lower=*/4,
+                          /*key_upper=*/4),
               IsOkAndHolds(ElementsAre(EqualsDocHitInfo(
                   /*document_id=*/3, std::vector<SectionId>{kSectionId1}))));
-  EXPECT_THAT(Query(integer_index.get(), kPropertyPath2, /*key_lower=*/4,
-                    /*key_upper=*/4),
+  EXPECT_THAT(this->Query(integer_index.get(), kPropertyPath2, /*key_lower=*/4,
+                          /*key_upper=*/4),
               IsOkAndHolds(IsEmpty()));
 }
 
@@ -655,9 +972,9 @@ TYPED_TEST(NumericIndexIntegerTest, OptimizeShouldDiscardEmptyPropertyStorage) {
 
   // All data in "prop2" as well as the underlying storage should be deleted, so
   // when querying "prop2", we should get empty result.
-  EXPECT_THAT(Query(integer_index.get(), kPropertyPath2,
-                    /*key_lower=*/std::numeric_limits<int64_t>::min(),
-                    /*key_upper=*/std::numeric_limits<int64_t>::max()),
+  EXPECT_THAT(this->Query(integer_index.get(), kPropertyPath2,
+                          /*key_lower=*/std::numeric_limits<int64_t>::min(),
+                          /*key_upper=*/std::numeric_limits<int64_t>::max()),
               IsOkAndHolds(IsEmpty()));
   if (std::is_same_v<IntegerIndex, TypeParam>) {
     std::string prop2_storage_working_path =
@@ -670,8 +987,8 @@ TYPED_TEST(NumericIndexIntegerTest, OptimizeShouldDiscardEmptyPropertyStorage) {
   // Verify we can still index and query for "prop2".
   Index(integer_index.get(), kPropertyPath2, /*document_id=*/100, kSectionId2,
         /*keys=*/{123});
-  EXPECT_THAT(Query(integer_index.get(), kPropertyPath2,
-                    /*key_lower=*/123, /*key_upper=*/123),
+  EXPECT_THAT(this->Query(integer_index.get(), kPropertyPath2,
+                          /*key_lower=*/123, /*key_upper=*/123),
               IsOkAndHolds(ElementsAre(EqualsDocHitInfo(
                   /*document_id=*/100, std::vector<SectionId>{kSectionId2}))));
 }
@@ -697,9 +1014,9 @@ TYPED_TEST(NumericIndexIntegerTest, OptimizeOutOfRangeDocumentId) {
   EXPECT_THAT(integer_index->last_added_document_id(), Eq(kInvalidDocumentId));
 
   // Verify all data are discarded after Optimize().
-  EXPECT_THAT(Query(integer_index.get(), kDefaultTestPropertyPath,
-                    /*key_lower=*/std::numeric_limits<int64_t>::min(),
-                    /*key_upper=*/std::numeric_limits<int64_t>::max()),
+  EXPECT_THAT(this->Query(integer_index.get(), kDefaultTestPropertyPath,
+                          /*key_lower=*/std::numeric_limits<int64_t>::min(),
+                          /*key_upper=*/std::numeric_limits<int64_t>::max()),
               IsOkAndHolds(IsEmpty()));
 }
 
@@ -731,9 +1048,9 @@ TYPED_TEST(NumericIndexIntegerTest, OptimizeDeleteAll) {
   EXPECT_THAT(integer_index->last_added_document_id(), Eq(kInvalidDocumentId));
 
   // Verify all data are discarded after Optimize().
-  EXPECT_THAT(Query(integer_index.get(), kDefaultTestPropertyPath,
-                    /*key_lower=*/std::numeric_limits<int64_t>::min(),
-                    /*key_upper=*/std::numeric_limits<int64_t>::max()),
+  EXPECT_THAT(this->Query(integer_index.get(), kDefaultTestPropertyPath,
+                          /*key_lower=*/std::numeric_limits<int64_t>::min(),
+                          /*key_upper=*/std::numeric_limits<int64_t>::max()),
               IsOkAndHolds(IsEmpty()));
 }
 
@@ -750,13 +1067,13 @@ TYPED_TEST(NumericIndexIntegerTest, Clear) {
 
   ASSERT_THAT(integer_index->last_added_document_id(), Eq(1));
   ASSERT_THAT(
-      Query(integer_index.get(), /*property_path=*/"A", /*key_lower=*/1,
-            /*key_upper=*/1),
+      this->Query(integer_index.get(), /*property_path=*/"A", /*key_lower=*/1,
+                  /*key_upper=*/1),
       IsOkAndHolds(ElementsAre(EqualsDocHitInfo(
           /*document_id=*/0, std::vector<SectionId>{kDefaultSectionId}))));
   ASSERT_THAT(
-      Query(integer_index.get(), /*property_path=*/"B", /*key_lower=*/3,
-            /*key_upper=*/3),
+      this->Query(integer_index.get(), /*property_path=*/"B", /*key_lower=*/3,
+                  /*key_upper=*/3),
       IsOkAndHolds(ElementsAre(EqualsDocHitInfo(
           /*document_id=*/1, std::vector<SectionId>{kDefaultSectionId}))));
 
@@ -764,12 +1081,14 @@ TYPED_TEST(NumericIndexIntegerTest, Clear) {
   // kInvalidDocumentId, and the previous added keys should be deleted.
   ICING_ASSERT_OK(integer_index->Clear());
   EXPECT_THAT(integer_index->last_added_document_id(), Eq(kInvalidDocumentId));
-  EXPECT_THAT(Query(integer_index.get(), /*property_path=*/"A", /*key_lower=*/1,
-                    /*key_upper=*/1),
-              IsOkAndHolds(IsEmpty()));
-  EXPECT_THAT(Query(integer_index.get(), /*property_path=*/"B", /*key_lower=*/3,
-                    /*key_upper=*/3),
-              IsOkAndHolds(IsEmpty()));
+  EXPECT_THAT(
+      this->Query(integer_index.get(), /*property_path=*/"A", /*key_lower=*/1,
+                  /*key_upper=*/1),
+      IsOkAndHolds(IsEmpty()));
+  EXPECT_THAT(
+      this->Query(integer_index.get(), /*property_path=*/"B", /*key_lower=*/3,
+                  /*key_upper=*/3),
+      IsOkAndHolds(IsEmpty()));
 
   // Integer index should be able to work normally after Clear().
   Index(integer_index.get(), /*property_path=*/"A", /*document_id=*/3,
@@ -780,13 +1099,13 @@ TYPED_TEST(NumericIndexIntegerTest, Clear) {
 
   EXPECT_THAT(integer_index->last_added_document_id(), Eq(4));
   EXPECT_THAT(
-      Query(integer_index.get(), /*property_path=*/"A", /*key_lower=*/123,
-            /*key_upper=*/123),
+      this->Query(integer_index.get(), /*property_path=*/"A", /*key_lower=*/123,
+                  /*key_upper=*/123),
       IsOkAndHolds(ElementsAre(EqualsDocHitInfo(
           /*document_id=*/3, std::vector<SectionId>{kDefaultSectionId}))));
   EXPECT_THAT(
-      Query(integer_index.get(), /*property_path=*/"B", /*key_lower=*/456,
-            /*key_upper=*/456),
+      this->Query(integer_index.get(), /*property_path=*/"B", /*key_lower=*/456,
+                  /*key_upper=*/456),
       IsOkAndHolds(ElementsAre(EqualsDocHitInfo(
           /*document_id=*/4, std::vector<SectionId>{kDefaultSectionId}))));
 }
@@ -1066,6 +1385,260 @@ TEST_F(IntegerIndexTest,
                 HasSubstr("Invalid storages crc"));
   }
 }
+
+TEST_F(IntegerIndexTest, WildcardStoragePersistenceQuery) {
+  // This test sets its schema assuming that max property storages == 32.
+  ASSERT_THAT(IntegerIndex::kMaxPropertyStorages, Eq(32));
+
+  PropertyConfigProto int_property_config =
+      PropertyConfigBuilder()
+          .SetName("otherProperty1")
+          .SetCardinality(CARDINALITY_REPEATED)
+          .SetDataTypeInt64(NUMERIC_MATCH_RANGE)
+          .Build();
+  // Create a schema with two types:
+  // - TypeA has 34 properties:
+  //     'desiredProperty', 'otherProperty'*, 'undesiredProperty'
+  // - TypeB has 2 properties: 'anotherProperty', 'desiredProperty'
+  // 1. The 32 'otherProperty's will consume all of the individual storages
+  // 2. TypeA.desiredProperty and TypeB.anotherProperty will both be assigned
+  //    SectionId = 0 for their respective types.
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("TypeA")
+                       .AddProperty(int_property_config)
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty2"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty3"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty4"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty5"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty6"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty7"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty8"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty9"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty10"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty11"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty12"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty13"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty14"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty15"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty16"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty17"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty18"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty19"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty20"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty21"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty22"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty23"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty24"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty25"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty26"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty27"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty28"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty29"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty30"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty31"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty32"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("desiredProperty"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("undesiredProperty")))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("TypeB")
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("anotherProperty"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("desiredProperty")))
+          .Build();
+  ICING_ASSERT_OK(this->schema_store_->SetSchema(schema));
+
+  // Ids are assigned alphabetically, so the property ids are:
+  // TypeA.desiredProperty = 0
+  // TypeA.otherPropertyN = N
+  // TypeA.undesiredProperty = 33
+  // TypeB.anotherProperty = 0
+  // TypeB.desiredProperty = 1
+  SectionId typea_desired_prop_id = 0;
+  SectionId typea_undesired_prop_id = 33;
+  SectionId typeb_another_prop_id = 0;
+  SectionId typeb_desired_prop_id = 1;
+  std::string desired_property = "desiredProperty";
+  std::string undesired_property = "undesiredProperty";
+  std::string another_property = "anotherProperty";
+
+  // Put 11 docs of "TypeA" into the document store.
+  DocumentProto doc =
+      DocumentBuilder().SetKey("ns1", "uri0").SetSchema("TypeA").Build();
+  ICING_ASSERT_OK(this->doc_store_->Put(doc));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri1").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri2").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri3").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri4").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri5").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri6").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri7").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri8").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri9").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri10").Build()));
+
+  // Put 10 docs of "TypeB" into the document store.
+  doc = DocumentBuilder(doc).SetUri("uri11").SetSchema("TypeB").Build();
+  ICING_ASSERT_OK(this->doc_store_->Put(doc));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri12").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri13").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri14").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri15").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri16").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri17").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri18").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri19").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri20").Build()));
+
+  {
+    ICING_ASSERT_OK_AND_ASSIGN(
+        std::unique_ptr<IntegerIndex> integer_index,
+        IntegerIndex::Create(filesystem_, working_path_));
+
+    // Index numeric content for other properties to force our property into the
+    // wildcard storage.
+    std::string other_property_path = "otherProperty";
+    for (int i = 1; i <= IntegerIndex::kMaxPropertyStorages; ++i) {
+      Index(integer_index.get(),
+            absl_ports::StrCat(other_property_path, std::to_string(i)),
+            /*document_id=*/0, /*section_id=*/i, /*keys=*/{i});
+    }
+
+    // Index numeric content for TypeA.desiredProperty
+    Index(integer_index.get(), desired_property, /*document_id=*/0,
+          typea_desired_prop_id, /*keys=*/{1});
+    Index(integer_index.get(), desired_property, /*document_id=*/1,
+          typea_desired_prop_id, /*keys=*/{3});
+    Index(integer_index.get(), desired_property, /*document_id=*/2,
+          typea_desired_prop_id, /*keys=*/{2});
+    Index(integer_index.get(), desired_property, /*document_id=*/3,
+          typea_desired_prop_id, /*keys=*/{0});
+    Index(integer_index.get(), desired_property, /*document_id=*/4,
+          typea_desired_prop_id, /*keys=*/{4});
+    Index(integer_index.get(), desired_property, /*document_id=*/5,
+          typea_desired_prop_id, /*keys=*/{2});
+
+    // Index the same numeric content for TypeA.undesiredProperty
+    Index(integer_index.get(), undesired_property, /*document_id=*/6,
+          typea_undesired_prop_id, /*keys=*/{3});
+    Index(integer_index.get(), undesired_property, /*document_id=*/7,
+          typea_undesired_prop_id, /*keys=*/{2});
+    Index(integer_index.get(), undesired_property, /*document_id=*/8,
+          typea_undesired_prop_id, /*keys=*/{0});
+    Index(integer_index.get(), undesired_property, /*document_id=*/9,
+          typea_undesired_prop_id, /*keys=*/{4});
+    Index(integer_index.get(), undesired_property, /*document_id=*/10,
+          typea_undesired_prop_id, /*keys=*/{2});
+
+    // Index the same numeric content for TypeB.undesiredProperty
+    Index(integer_index.get(), another_property, /*document_id=*/11,
+          typeb_another_prop_id, /*keys=*/{3});
+    Index(integer_index.get(), another_property, /*document_id=*/12,
+          typeb_another_prop_id, /*keys=*/{2});
+    Index(integer_index.get(), another_property, /*document_id=*/13,
+          typeb_another_prop_id, /*keys=*/{0});
+    Index(integer_index.get(), another_property, /*document_id=*/14,
+          typeb_another_prop_id, /*keys=*/{4});
+    Index(integer_index.get(), another_property, /*document_id=*/15,
+          typeb_another_prop_id, /*keys=*/{2});
+
+    // Finally, index the same numeric content for TypeB.desiredProperty
+    Index(integer_index.get(), desired_property, /*document_id=*/16,
+          typeb_desired_prop_id, /*keys=*/{3});
+    Index(integer_index.get(), desired_property, /*document_id=*/17,
+          typeb_desired_prop_id, /*keys=*/{2});
+    Index(integer_index.get(), desired_property, /*document_id=*/18,
+          typeb_desired_prop_id, /*keys=*/{0});
+    Index(integer_index.get(), desired_property, /*document_id=*/19,
+          typeb_desired_prop_id, /*keys=*/{4});
+    Index(integer_index.get(), desired_property, /*document_id=*/20,
+          typeb_desired_prop_id, /*keys=*/{2});
+  }
+
+  ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<IntegerIndex> integer_index,
+                             IntegerIndex::Create(filesystem_, working_path_));
+
+  EXPECT_THAT(integer_index->num_property_indices(), Eq(33));
+
+  // Only the hits for 'desired_prop_id' should be returned.
+  std::vector<SectionId> expected_sections_typea = {typea_desired_prop_id};
+  std::vector<SectionId> expected_sections_typeb = {typeb_desired_prop_id};
+  EXPECT_THAT(
+      Query(integer_index.get(), desired_property,
+            /*key_lower=*/2, /*key_upper=*/2),
+      IsOkAndHolds(ElementsAre(
+          EqualsDocHitInfo(/*document_id=*/20, expected_sections_typeb),
+          EqualsDocHitInfo(/*document_id=*/17, expected_sections_typeb),
+          EqualsDocHitInfo(/*document_id=*/5, expected_sections_typea),
+          EqualsDocHitInfo(/*document_id=*/2, expected_sections_typea))));
+
+  EXPECT_THAT(
+      Query(integer_index.get(), desired_property,
+            /*key_lower=*/1, /*key_upper=*/3),
+      IsOkAndHolds(ElementsAre(
+          EqualsDocHitInfo(/*document_id=*/20, expected_sections_typeb),
+          EqualsDocHitInfo(/*document_id=*/17, expected_sections_typeb),
+          EqualsDocHitInfo(/*document_id=*/16, expected_sections_typeb),
+          EqualsDocHitInfo(/*document_id=*/5, expected_sections_typea),
+          EqualsDocHitInfo(/*document_id=*/2, expected_sections_typea),
+          EqualsDocHitInfo(/*document_id=*/1, expected_sections_typea),
+          EqualsDocHitInfo(/*document_id=*/0, expected_sections_typea))));
+}
+
 TEST_F(IntegerIndexTest,
        IntegerIndexShouldWorkAfterOptimizeAndReinitialization) {
   constexpr std::string_view kPropertyPath1 = "prop1";
@@ -1183,6 +1756,550 @@ TEST_F(IntegerIndexTest,
   }
 }
 
+TEST_F(IntegerIndexTest, WildcardStorageWorksAfterOptimize) {
+  // This test sets its schema assuming that max property storages == 32.
+  ASSERT_THAT(IntegerIndex::kMaxPropertyStorages, Eq(32));
+
+  PropertyConfigProto int_property_config =
+      PropertyConfigBuilder()
+          .SetName("otherProperty1")
+          .SetCardinality(CARDINALITY_REPEATED)
+          .SetDataTypeInt64(NUMERIC_MATCH_RANGE)
+          .Build();
+  // Create a schema with two types:
+  // - TypeA has 34 properties:
+  //     'desiredProperty', 'otherProperty'*, 'undesiredProperty'
+  // - TypeB has 2 properties: 'anotherProperty', 'desiredProperty'
+  // 1. The 32 'otherProperty's will consume all of the individual storages
+  // 2. TypeA.desiredProperty and TypeB.anotherProperty will both be assigned
+  //    SectionId = 0 for their respective types.
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("TypeA")
+                       .AddProperty(int_property_config)
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty2"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty3"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty4"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty5"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty6"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty7"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty8"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty9"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty10"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty11"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty12"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty13"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty14"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty15"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty16"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty17"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty18"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty19"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty20"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty21"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty22"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty23"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty24"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty25"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty26"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty27"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty28"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty29"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty30"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty31"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty32"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("desiredProperty"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("undesiredProperty")))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("TypeB")
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("anotherProperty"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("desiredProperty")))
+          .Build();
+  ICING_ASSERT_OK(this->schema_store_->SetSchema(schema));
+
+  // Ids are assigned alphabetically, so the property ids are:
+  // TypeA.desiredProperty = 0
+  // TypeA.otherPropertyN = N
+  // TypeA.undesiredProperty = 33
+  // TypeB.anotherProperty = 0
+  // TypeB.desiredProperty = 1
+  SectionId typea_desired_prop_id = 0;
+  SectionId typea_undesired_prop_id = 33;
+  SectionId typeb_another_prop_id = 0;
+  SectionId typeb_desired_prop_id = 1;
+  std::string desired_property = "desiredProperty";
+  std::string undesired_property = "undesiredProperty";
+  std::string another_property = "anotherProperty";
+
+  // Only the hits for 'desired_prop_id' should be returned.
+  std::vector<SectionId> expected_sections_typea = {typea_desired_prop_id};
+  std::vector<SectionId> expected_sections_typeb = {typeb_desired_prop_id};
+
+  // Put 11 docs of "TypeA" into the document store.
+  DocumentProto doc =
+      DocumentBuilder().SetKey("ns1", "uri0").SetSchema("TypeA").Build();
+  ICING_ASSERT_OK(this->doc_store_->Put(doc));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri1").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri2").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri3").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri4").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri5").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri6").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri7").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri8").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri9").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri10").Build()));
+
+  // Put 10 docs of "TypeB" into the document store.
+  doc = DocumentBuilder(doc).SetUri("uri11").SetSchema("TypeB").Build();
+  ICING_ASSERT_OK(this->doc_store_->Put(doc));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri12").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri13").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri14").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri15").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri16").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri17").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri18").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri19").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri20").Build()));
+
+  {
+    ICING_ASSERT_OK_AND_ASSIGN(
+        std::unique_ptr<IntegerIndex> integer_index,
+        IntegerIndex::Create(filesystem_, working_path_));
+
+    // Index numeric content for other properties to force our property into the
+    // wildcard storage.
+    std::string other_property_path = "otherProperty";
+    for (int i = 1; i <= IntegerIndex::kMaxPropertyStorages; ++i) {
+      Index(integer_index.get(),
+            absl_ports::StrCat(other_property_path, std::to_string(i)),
+            /*document_id=*/0, /*section_id=*/i, /*keys=*/{i});
+    }
+
+    // Index numeric content for TypeA.desiredProperty
+    Index(integer_index.get(), desired_property, /*document_id=*/0,
+          typea_desired_prop_id, /*keys=*/{1});
+    Index(integer_index.get(), desired_property, /*document_id=*/1,
+          typea_desired_prop_id, /*keys=*/{3});
+    Index(integer_index.get(), desired_property, /*document_id=*/2,
+          typea_desired_prop_id, /*keys=*/{2});
+    Index(integer_index.get(), desired_property, /*document_id=*/3,
+          typea_desired_prop_id, /*keys=*/{0});
+    Index(integer_index.get(), desired_property, /*document_id=*/4,
+          typea_desired_prop_id, /*keys=*/{4});
+    Index(integer_index.get(), desired_property, /*document_id=*/5,
+          typea_desired_prop_id, /*keys=*/{2});
+
+    // Index the same numeric content for TypeA.undesiredProperty
+    Index(integer_index.get(), undesired_property, /*document_id=*/6,
+          typea_undesired_prop_id, /*keys=*/{3});
+    Index(integer_index.get(), undesired_property, /*document_id=*/7,
+          typea_undesired_prop_id, /*keys=*/{2});
+    Index(integer_index.get(), undesired_property, /*document_id=*/8,
+          typea_undesired_prop_id, /*keys=*/{0});
+    Index(integer_index.get(), undesired_property, /*document_id=*/9,
+          typea_undesired_prop_id, /*keys=*/{4});
+    Index(integer_index.get(), undesired_property, /*document_id=*/10,
+          typea_undesired_prop_id, /*keys=*/{2});
+
+    // Index the same numeric content for TypeB.undesiredProperty
+    Index(integer_index.get(), another_property, /*document_id=*/11,
+          typeb_another_prop_id, /*keys=*/{3});
+    Index(integer_index.get(), another_property, /*document_id=*/12,
+          typeb_another_prop_id, /*keys=*/{2});
+    Index(integer_index.get(), another_property, /*document_id=*/13,
+          typeb_another_prop_id, /*keys=*/{0});
+    Index(integer_index.get(), another_property, /*document_id=*/14,
+          typeb_another_prop_id, /*keys=*/{4});
+    Index(integer_index.get(), another_property, /*document_id=*/15,
+          typeb_another_prop_id, /*keys=*/{2});
+
+    // Finally, index the same numeric content for TypeB.desiredProperty
+    Index(integer_index.get(), desired_property, /*document_id=*/16,
+          typeb_desired_prop_id, /*keys=*/{3});
+    Index(integer_index.get(), desired_property, /*document_id=*/17,
+          typeb_desired_prop_id, /*keys=*/{2});
+    Index(integer_index.get(), desired_property, /*document_id=*/18,
+          typeb_desired_prop_id, /*keys=*/{0});
+    Index(integer_index.get(), desired_property, /*document_id=*/19,
+          typeb_desired_prop_id, /*keys=*/{4});
+    Index(integer_index.get(), desired_property, /*document_id=*/20,
+          typeb_desired_prop_id, /*keys=*/{2});
+
+    ICING_ASSERT_OK(doc_store_->Delete(/*document_id=*/3));
+    ICING_ASSERT_OK(doc_store_->Delete(/*document_id=*/5));
+    // Delete doc id = 3, 5, compress and keep the rest.
+    ICING_ASSERT_OK_AND_ASSIGN(std::vector<DocumentId> document_id_old_to_new,
+                               CompactDocStore());
+
+    DocumentId new_last_added_document_id = 18;
+    EXPECT_THAT(integer_index->Optimize(document_id_old_to_new,
+                                        new_last_added_document_id),
+                IsOk());
+    EXPECT_THAT(integer_index->last_added_document_id(),
+                Eq(new_last_added_document_id));
+
+    EXPECT_THAT(
+        Query(integer_index.get(), desired_property,
+              /*key_lower=*/2, /*key_upper=*/2),
+        IsOkAndHolds(ElementsAre(
+            EqualsDocHitInfo(/*document_id=*/20 - 2, expected_sections_typeb),
+            EqualsDocHitInfo(/*document_id=*/17 - 2, expected_sections_typeb),
+            EqualsDocHitInfo(/*document_id=*/2, expected_sections_typea))));
+
+    EXPECT_THAT(
+        Query(integer_index.get(), desired_property,
+              /*key_lower=*/1, /*key_upper=*/3),
+        IsOkAndHolds(ElementsAre(
+            EqualsDocHitInfo(/*document_id=*/20 - 2, expected_sections_typeb),
+            EqualsDocHitInfo(/*document_id=*/17 - 2, expected_sections_typeb),
+            EqualsDocHitInfo(/*document_id=*/16 - 2, expected_sections_typeb),
+            EqualsDocHitInfo(/*document_id=*/2, expected_sections_typea),
+            EqualsDocHitInfo(/*document_id=*/1, expected_sections_typea),
+            EqualsDocHitInfo(/*document_id=*/0, expected_sections_typea))));
+  }
+
+  ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<IntegerIndex> integer_index,
+                             IntegerIndex::Create(filesystem_, working_path_));
+
+  EXPECT_THAT(integer_index->num_property_indices(), Eq(33));
+
+  EXPECT_THAT(
+      Query(integer_index.get(), desired_property,
+            /*key_lower=*/2, /*key_upper=*/2),
+      IsOkAndHolds(ElementsAre(
+          EqualsDocHitInfo(/*document_id=*/20 - 2, expected_sections_typeb),
+          EqualsDocHitInfo(/*document_id=*/17 - 2, expected_sections_typeb),
+          EqualsDocHitInfo(/*document_id=*/2, expected_sections_typea))));
+
+  EXPECT_THAT(
+      Query(integer_index.get(), desired_property,
+            /*key_lower=*/1, /*key_upper=*/3),
+      IsOkAndHolds(ElementsAre(
+          EqualsDocHitInfo(/*document_id=*/20 - 2, expected_sections_typeb),
+          EqualsDocHitInfo(/*document_id=*/17 - 2, expected_sections_typeb),
+          EqualsDocHitInfo(/*document_id=*/16 - 2, expected_sections_typeb),
+          EqualsDocHitInfo(/*document_id=*/2, expected_sections_typea),
+          EqualsDocHitInfo(/*document_id=*/1, expected_sections_typea),
+          EqualsDocHitInfo(/*document_id=*/0, expected_sections_typea))));
+}
+
+// This test covers the situation where Optimize causes us to throw out some of
+// the individual index storages (because they don't have any hits anymore).
+// In this case, any properties that added content to the wildcard storage (even
+// if all of their content was also deleted) should still be placed in the
+// wilcard storage.
+TEST_F(IntegerIndexTest, WildcardStorageAvailableIndicesAfterOptimize) {
+  // This test sets its schema assuming that max property storages == 32.
+  ASSERT_THAT(IntegerIndex::kMaxPropertyStorages, Eq(32));
+
+  PropertyConfigProto int_property_config =
+      PropertyConfigBuilder()
+          .SetName("otherProperty1")
+          .SetCardinality(CARDINALITY_REPEATED)
+          .SetDataTypeInt64(NUMERIC_MATCH_RANGE)
+          .Build();
+  // Create a schema with two types:
+  // - TypeA has 34 properties:
+  //     'desiredProperty', 'otherProperty'*, 'undesiredProperty'
+  // - TypeB has 2 properties: 'anotherProperty', 'desiredProperty'
+  // 1. The 32 'otherProperty's will consume all of the individual storages
+  // 2. TypeA.desiredProperty and TypeB.anotherProperty will both be assigned
+  //    SectionId = 0 for their respective types.
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("TypeA")
+                       .AddProperty(int_property_config)
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty2"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty3"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty4"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty5"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty6"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty7"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty8"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty9"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty10"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty11"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty12"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty13"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty14"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty15"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty16"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty17"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty18"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty19"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty20"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty21"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty22"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty23"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty24"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty25"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty26"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty27"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty28"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty29"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty30"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty31"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("otherProperty32"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("desiredProperty"))
+                       .AddProperty(PropertyConfigBuilder(int_property_config)
+                                        .SetName("undesiredProperty")))
+          .Build();
+  ICING_ASSERT_OK(this->schema_store_->SetSchema(schema));
+
+  // Ids are assigned alphabetically, so the property ids are:
+  // TypeA.desiredProperty = 0
+  // TypeA.otherPropertyN = N
+  // TypeA.undesiredProperty = 33
+  // TypeB.anotherProperty = 0
+  // TypeB.desiredProperty = 1
+  SectionId typea_desired_prop_id = 0;
+  SectionId typea_undesired_prop_id = 33;
+  SectionId typea_other1_prop_id = 1;
+  std::string desired_property = "desiredProperty";
+  std::string undesired_property = "undesiredProperty";
+  std::string another_property = "anotherProperty";
+  std::string other_property_1 = "otherProperty1";
+
+  // Only the hits for 'desired_prop_id' should be returned.
+  std::vector<SectionId> expected_sections_typea = {typea_desired_prop_id};
+
+  // Put 11 docs of "TypeA" into the document store.
+  DocumentProto doc =
+      DocumentBuilder().SetKey("ns1", "uri0").SetSchema("TypeA").Build();
+  ICING_ASSERT_OK(this->doc_store_->Put(doc));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri1").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri2").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri3").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri4").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri5").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri6").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri7").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri8").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri9").Build()));
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri10").Build()));
+
+  {
+    ICING_ASSERT_OK_AND_ASSIGN(
+        std::unique_ptr<IntegerIndex> integer_index,
+        IntegerIndex::Create(filesystem_, working_path_));
+
+    // Index numeric content for other properties to force our property into the
+    // wildcard storage.
+    std::string other_property_path = "otherProperty";
+    for (int i = 1; i <= IntegerIndex::kMaxPropertyStorages; ++i) {
+      Index(integer_index.get(),
+            absl_ports::StrCat(other_property_path, std::to_string(i)),
+            /*document_id=*/0, /*section_id=*/i, /*keys=*/{i});
+    }
+
+    // Index numeric content for TypeA.desiredProperty
+    Index(integer_index.get(), desired_property, /*document_id=*/0,
+          typea_desired_prop_id, /*keys=*/{1});
+    Index(integer_index.get(), desired_property, /*document_id=*/1,
+          typea_desired_prop_id, /*keys=*/{3});
+    Index(integer_index.get(), desired_property, /*document_id=*/2,
+          typea_desired_prop_id, /*keys=*/{2});
+    Index(integer_index.get(), desired_property, /*document_id=*/3,
+          typea_desired_prop_id, /*keys=*/{0});
+    Index(integer_index.get(), desired_property, /*document_id=*/4,
+          typea_desired_prop_id, /*keys=*/{4});
+    Index(integer_index.get(), desired_property, /*document_id=*/5,
+          typea_desired_prop_id, /*keys=*/{2});
+
+    // Index the same numeric content for TypeA.undesiredProperty
+    Index(integer_index.get(), undesired_property, /*document_id=*/6,
+          typea_undesired_prop_id, /*keys=*/{3});
+    Index(integer_index.get(), undesired_property, /*document_id=*/7,
+          typea_undesired_prop_id, /*keys=*/{2});
+    Index(integer_index.get(), undesired_property, /*document_id=*/8,
+          typea_undesired_prop_id, /*keys=*/{0});
+    Index(integer_index.get(), undesired_property, /*document_id=*/9,
+          typea_undesired_prop_id, /*keys=*/{4});
+    Index(integer_index.get(), undesired_property, /*document_id=*/10,
+          typea_undesired_prop_id, /*keys=*/{2});
+
+    // Delete all the docs that had hits in otherProperty* and
+    // undesiredProperty.
+    ICING_ASSERT_OK(doc_store_->Delete(/*document_id=*/0));
+    ICING_ASSERT_OK(doc_store_->Delete(/*document_id=*/6));
+    ICING_ASSERT_OK(doc_store_->Delete(/*document_id=*/7));
+    ICING_ASSERT_OK(doc_store_->Delete(/*document_id=*/8));
+    ICING_ASSERT_OK(doc_store_->Delete(/*document_id=*/9));
+    ICING_ASSERT_OK(doc_store_->Delete(/*document_id=*/10));
+    // Delete doc id = 0, 6, 7, 8, 9, 10. Compress and keep the rest.
+    ICING_ASSERT_OK_AND_ASSIGN(std::vector<DocumentId> document_id_old_to_new,
+                               CompactDocStore());
+
+    DocumentId new_last_added_document_id = 5 - 1;
+    EXPECT_THAT(integer_index->Optimize(document_id_old_to_new,
+                                        new_last_added_document_id),
+                IsOk());
+    EXPECT_THAT(integer_index->last_added_document_id(),
+                Eq(new_last_added_document_id));
+
+    EXPECT_THAT(
+        Query(integer_index.get(), desired_property,
+              /*key_lower=*/2, /*key_upper=*/2),
+        IsOkAndHolds(ElementsAre(
+            EqualsDocHitInfo(/*document_id=*/5 - 1, expected_sections_typea),
+            EqualsDocHitInfo(/*document_id=*/2 - 1, expected_sections_typea))));
+
+    EXPECT_THAT(
+        Query(integer_index.get(), desired_property,
+              /*key_lower=*/1, /*key_upper=*/3),
+        IsOkAndHolds(ElementsAre(
+            EqualsDocHitInfo(/*document_id=*/5 - 1, expected_sections_typea),
+            EqualsDocHitInfo(/*document_id=*/2 - 1, expected_sections_typea),
+            EqualsDocHitInfo(/*document_id=*/1 - 1, expected_sections_typea))));
+  }
+
+  ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<IntegerIndex> integer_index,
+                             IntegerIndex::Create(filesystem_, working_path_));
+
+  EXPECT_THAT(integer_index->num_property_indices(), Eq(1));
+
+  // Add a new doc (docid==5) and a hit for desiredProperty. This should still
+  // be placed into the wildcard integer storage.
+  doc = DocumentBuilder().SetKey("ns1", "uri11").SetSchema("TypeA").Build();
+  ICING_ASSERT_OK(this->doc_store_->Put(doc));
+  Index(integer_index.get(), desired_property, /*document_id=*/5,
+        typea_desired_prop_id, /*keys=*/{12});
+  EXPECT_THAT(integer_index->num_property_indices(), Eq(1));
+
+  EXPECT_THAT(Query(integer_index.get(), desired_property,
+                    /*key_lower=*/12, /*key_upper=*/12),
+              IsOkAndHolds(ElementsAre(EqualsDocHitInfo(
+                  /*document_id=*/5, expected_sections_typea))));
+
+  // Add a new doc (docid==6) and a hit for undesiredProperty. This should still
+  // be placed into the wildcard integer storage.
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri12").Build()));
+  Index(integer_index.get(), undesired_property, /*document_id=*/6,
+        typea_undesired_prop_id, /*keys=*/{3});
+  EXPECT_THAT(integer_index->num_property_indices(), Eq(1));
+
+  expected_sections_typea = {typea_undesired_prop_id};
+  EXPECT_THAT(Query(integer_index.get(), undesired_property,
+                    /*key_lower=*/3, /*key_upper=*/3),
+              IsOkAndHolds(ElementsAre(EqualsDocHitInfo(
+                  /*document_id=*/6, expected_sections_typea))));
+
+  // Add a new doc (docid==7) and a hit for otherProperty1. This should be given
+  // its own individual storage.
+  ICING_ASSERT_OK(
+      this->doc_store_->Put(DocumentBuilder(doc).SetUri("uri13").Build()));
+  Index(integer_index.get(), other_property_1, /*document_id=*/7,
+        typea_other1_prop_id, /*keys=*/{3});
+  EXPECT_THAT(integer_index->num_property_indices(), Eq(2));
+
+  expected_sections_typea = {typea_other1_prop_id};
+  EXPECT_THAT(Query(integer_index.get(), other_property_1,
+                    /*key_lower=*/3, /*key_upper=*/3),
+              IsOkAndHolds(ElementsAre(EqualsDocHitInfo(
+                  /*document_id=*/7, expected_sections_typea))));
+}
+
 }  // namespace
 
 }  // namespace lib
diff --git a/icing/index/numeric/numeric-index.h b/icing/index/numeric/numeric-index.h
index 347260a..28640ca 100644
--- a/icing/index/numeric/numeric-index.h
+++ b/icing/index/numeric/numeric-index.h
@@ -23,8 +23,10 @@
 #include "icing/text_classifier/lib3/utils/base/statusor.h"
 #include "icing/file/persistent-storage.h"
 #include "icing/index/iterator/doc-hit-info-iterator.h"
+#include "icing/schema/schema-store.h"
 #include "icing/schema/section.h"
 #include "icing/store/document-id.h"
+#include "icing/store/document-store.h"
 
 namespace icing {
 namespace lib {
@@ -126,8 +128,9 @@ class NumericIndex : public PersistentStorage {
   //   - INVALID_ARGUMENT_ERROR if key_lower > key_upper
   //   - Any other errors, depending on the actual implementation
   virtual libtextclassifier3::StatusOr<std::unique_ptr<DocHitInfoIterator>>
-  GetIterator(std::string_view property_path, T key_lower,
-              T key_upper) const = 0;
+  GetIterator(std::string_view property_path, T key_lower, T key_upper,
+              const DocumentStore& document_store,
+              const SchemaStore& schema_store) const = 0;
 
   // Reduces internal file sizes by reclaiming space and ids of deleted
   // documents. Numeric index will convert all data (hits) to the new document
@@ -162,6 +165,10 @@ class NumericIndex : public PersistentStorage {
   // last_added_document_id() or last_added_document_id() is invalid.
   virtual void set_last_added_document_id(DocumentId document_id) = 0;
 
+  // The number of individual indices that the NumericIndex has created to
+  // search over all indexed properties thus far.
+  virtual int num_property_indices() const = 0;
+
  protected:
   explicit NumericIndex(const Filesystem& filesystem,
                         std::string&& working_path,
diff --git a/icing/index/numeric/posting-list-integer-index-accessor.cc b/icing/index/numeric/posting-list-integer-index-accessor.cc
index 220b240..af2aea4 100644
--- a/icing/index/numeric/posting-list-integer-index-accessor.cc
+++ b/icing/index/numeric/posting-list-integer-index-accessor.cc
@@ -64,6 +64,58 @@ PostingListIntegerIndexAccessor::CreateFromExisting(
 // Returns the next batch of integer index data for the provided posting list.
 libtextclassifier3::StatusOr<std::vector<IntegerIndexData>>
 PostingListIntegerIndexAccessor::GetNextDataBatch() {
+  return GetNextDataBatchImpl(/*free_posting_list=*/false);
+}
+
+libtextclassifier3::StatusOr<std::vector<IntegerIndexData>>
+PostingListIntegerIndexAccessor::GetAllDataAndFree() {
+  if (preexisting_posting_list_ == nullptr) {
+    return absl_ports::FailedPreconditionError(
+        "Cannot retrieve data from a PostingListIntegerIndexAccessor that "
+        "was not created from a preexisting posting list.");
+  }
+
+  std::vector<IntegerIndexData> all_data;
+  while (true) {
+    ICING_ASSIGN_OR_RETURN(std::vector<IntegerIndexData> batch,
+                           GetNextDataBatchImpl(/*free_posting_list=*/true));
+    if (batch.empty()) {
+      break;
+    }
+    std::move(batch.begin(), batch.end(), std::back_inserter(all_data));
+  }
+
+  return all_data;
+}
+
+libtextclassifier3::Status PostingListIntegerIndexAccessor::PrependData(
+    const IntegerIndexData& data) {
+  PostingListUsed& active_pl = (preexisting_posting_list_ != nullptr)
+                                   ? preexisting_posting_list_->posting_list
+                                   : in_memory_posting_list_;
+  libtextclassifier3::Status status =
+      serializer_->PrependData(&active_pl, data);
+  if (!absl_ports::IsResourceExhausted(status)) {
+    return status;
+  }
+  // There is no more room to add data to this current posting list! Therefore,
+  // we need to either move those data to a larger posting list or flush this
+  // posting list and create another max-sized posting list in the chain.
+  if (preexisting_posting_list_ != nullptr) {
+    ICING_RETURN_IF_ERROR(FlushPreexistingPostingList());
+  } else {
+    ICING_RETURN_IF_ERROR(FlushInMemoryPostingList());
+  }
+
+  // Re-add data. Should always fit since we just cleared
+  // in_memory_posting_list_. It's fine to explicitly reference
+  // in_memory_posting_list_ here because there's no way of reaching this line
+  // while preexisting_posting_list_ is still in use.
+  return serializer_->PrependData(&in_memory_posting_list_, data);
+}
+
+libtextclassifier3::StatusOr<std::vector<IntegerIndexData>>
+PostingListIntegerIndexAccessor::GetNextDataBatchImpl(bool free_posting_list) {
   if (preexisting_posting_list_ == nullptr) {
     if (has_reached_posting_list_chain_end_) {
       return std::vector<IntegerIndexData>();
@@ -85,6 +137,11 @@ PostingListIntegerIndexAccessor::GetNextDataBatch() {
     next_block_index = preexisting_posting_list_->next_block_index;
   }
 
+  if (free_posting_list) {
+    ICING_RETURN_IF_ERROR(
+        storage_->FreePostingList(std::move(*preexisting_posting_list_)));
+  }
+
   if (next_block_index != kInvalidBlockIndex) {
     // Since we only have to deal with next block for max-sized posting list
     // block, max_num_posting_lists is 1 and posting_list_index_bits is
@@ -103,31 +160,5 @@ PostingListIntegerIndexAccessor::GetNextDataBatch() {
   return batch;
 }
 
-libtextclassifier3::Status PostingListIntegerIndexAccessor::PrependData(
-    const IntegerIndexData& data) {
-  PostingListUsed& active_pl = (preexisting_posting_list_ != nullptr)
-                                   ? preexisting_posting_list_->posting_list
-                                   : in_memory_posting_list_;
-  libtextclassifier3::Status status =
-      serializer_->PrependData(&active_pl, data);
-  if (!absl_ports::IsResourceExhausted(status)) {
-    return status;
-  }
-  // There is no more room to add data to this current posting list! Therefore,
-  // we need to either move those data to a larger posting list or flush this
-  // posting list and create another max-sized posting list in the chain.
-  if (preexisting_posting_list_ != nullptr) {
-    ICING_RETURN_IF_ERROR(FlushPreexistingPostingList());
-  } else {
-    ICING_RETURN_IF_ERROR(FlushInMemoryPostingList());
-  }
-
-  // Re-add data. Should always fit since we just cleared
-  // in_memory_posting_list_. It's fine to explicitly reference
-  // in_memory_posting_list_ here because there's no way of reaching this line
-  // while preexisting_posting_list_ is still in use.
-  return serializer_->PrependData(&in_memory_posting_list_, data);
-}
-
 }  // namespace lib
 }  // namespace icing
diff --git a/icing/index/numeric/posting-list-integer-index-accessor.h b/icing/index/numeric/posting-list-integer-index-accessor.h
index 4c1eced..f0d3d25 100644
--- a/icing/index/numeric/posting-list-integer-index-accessor.h
+++ b/icing/index/numeric/posting-list-integer-index-accessor.h
@@ -50,7 +50,7 @@ class PostingListIntegerIndexAccessor : public PostingListAccessor {
   Create(FlashIndexStorage* storage,
          PostingListIntegerIndexSerializer* serializer);
 
-  // Create a PostingListIntegerIndexAccessor with an existing posting list
+  // Creates a PostingListIntegerIndexAccessor with an existing posting list
   // identified by existing_posting_list_id.
   //
   // RETURNS:
@@ -64,17 +64,30 @@ class PostingListIntegerIndexAccessor : public PostingListAccessor {
 
   PostingListSerializer* GetSerializer() override { return serializer_; }
 
-  // Retrieve the next batch of data in the posting list chain
+  // Retrieves the next batch of data in the posting list chain.
   //
   // RETURNS:
   //   - On success, a vector of integer index data in the posting list chain
-  //   - INTERNAL if called on an instance that was created via Create, if
-  //     unable to read the next posting list in the chain or if the posting
-  //     list has been corrupted somehow.
+  //   - FAILED_PRECONDITION_ERROR if called on an instance that was created via
+  //     Create.
+  //   - INTERNAL_ERROR if unable to read the next posting list in the chain or
+  //     if the posting list has been corrupted somehow.
   libtextclassifier3::StatusOr<std::vector<IntegerIndexData>>
   GetNextDataBatch();
 
-  // Prepend one data. This may result in flushing the posting list to disk (if
+  // Retrieves all data from the posting list chain and frees all posting
+  // list(s).
+  //
+  // RETURNS:
+  //   - On success, a vector of integer index data in the posting list chain
+  //   - FAILED_PRECONDITION_ERROR if called on an instance that was created via
+  //     Create.
+  //   - INTERNAL_ERROR if unable to read the next posting list in the chain or
+  //     if the posting list has been corrupted somehow.
+  libtextclassifier3::StatusOr<std::vector<IntegerIndexData>>
+  GetAllDataAndFree();
+
+  // Prepends one data. This may result in flushing the posting list to disk (if
   // the PostingListIntegerIndexAccessor holds a max-sized posting list that
   // is full) or freeing a pre-existing posting list if it is too small to fit
   // all data necessary.
@@ -87,7 +100,15 @@ class PostingListIntegerIndexAccessor : public PostingListAccessor {
   //     posting list.
   libtextclassifier3::Status PrependData(const IntegerIndexData& data);
 
-  // TODO(b/259743562): [Optimization 1] add GetAndClear, IsFull for split
+  bool WantsSplit() const {
+    const PostingListUsed* current_pl =
+        preexisting_posting_list_ != nullptr
+            ? &preexisting_posting_list_->posting_list
+            : &in_memory_posting_list_;
+    // Only max-sized PLs get split. Smaller PLs just get copied to larger PLs.
+    return current_pl->size_in_bytes() == storage_->max_posting_list_bytes() &&
+           serializer_->IsFull(current_pl);
+  }
 
  private:
   explicit PostingListIntegerIndexAccessor(
@@ -96,6 +117,20 @@ class PostingListIntegerIndexAccessor : public PostingListAccessor {
       : PostingListAccessor(storage, std::move(in_memory_posting_list)),
         serializer_(serializer) {}
 
+  // Retrieves the next batch of data in the posting list chain.
+  //
+  // - free_posting_list: a boolean flag indicating whether freeing all posting
+  //   lists after retrieving batch data.
+  //
+  // RETURNS:
+  //   - On success, a vector of integer index data in the posting list chain
+  //   - FAILED_PRECONDITION_ERROR if called on an instance that was created via
+  //     Create.
+  //   - INTERNAL_ERROR if unable to read the next posting list in the chain or
+  //     if the posting list has been corrupted somehow.
+  libtextclassifier3::StatusOr<std::vector<IntegerIndexData>>
+  GetNextDataBatchImpl(bool free_posting_list);
+
   PostingListIntegerIndexSerializer* serializer_;  // Does not own.
 };
 
diff --git a/icing/index/numeric/posting-list-integer-index-accessor_test.cc b/icing/index/numeric/posting-list-integer-index-accessor_test.cc
index 48221b9..f655fea 100644
--- a/icing/index/numeric/posting-list-integer-index-accessor_test.cc
+++ b/icing/index/numeric/posting-list-integer-index-accessor_test.cc
@@ -25,6 +25,7 @@
 #include "gtest/gtest.h"
 #include "icing/file/filesystem.h"
 #include "icing/file/posting_list/flash-index-storage.h"
+#include "icing/file/posting_list/posting-list-common.h"
 #include "icing/file/posting_list/posting-list-identifier.h"
 #include "icing/index/numeric/integer-index-data.h"
 #include "icing/index/numeric/posting-list-integer-index-serializer.h"
@@ -42,6 +43,7 @@ using ::testing::ElementsAre;
 using ::testing::ElementsAreArray;
 using ::testing::Eq;
 using ::testing::Lt;
+using ::testing::Ne;
 using ::testing::SizeIs;
 
 class PostingListIntegerIndexAccessorTest : public ::testing::Test {
@@ -402,6 +404,131 @@ TEST_F(PostingListIntegerIndexAccessorTest,
   EXPECT_THAT(result2.status, IsOk());
 }
 
+TEST_F(PostingListIntegerIndexAccessorTest, GetAllDataAndFree) {
+  IntegerIndexData data1(/*section_id=*/3, /*document_id=*/1, /*key=*/123);
+  IntegerIndexData data2(/*section_id=*/3, /*document_id=*/2, /*key=*/456);
+
+  ICING_ASSERT_OK_AND_ASSIGN(
+      std::unique_ptr<PostingListIntegerIndexAccessor> pl_accessor1,
+      PostingListIntegerIndexAccessor::Create(flash_index_storage_.get(),
+                                              serializer_.get()));
+  // Add 2 data.
+  ICING_ASSERT_OK(pl_accessor1->PrependData(data1));
+  ICING_ASSERT_OK(pl_accessor1->PrependData(data2));
+  PostingListAccessor::FinalizeResult result1 =
+      std::move(*pl_accessor1).Finalize();
+  ICING_ASSERT_OK(result1.status);
+
+  ICING_ASSERT_OK_AND_ASSIGN(
+      std::unique_ptr<PostingListIntegerIndexAccessor> pl_accessor2,
+      PostingListIntegerIndexAccessor::CreateFromExisting(
+          flash_index_storage_.get(), serializer_.get(), result1.id));
+  EXPECT_THAT(pl_accessor2->GetAllDataAndFree(),
+              IsOkAndHolds(ElementsAre(data2, data1)));
+
+  // Allocate a new posting list with same size again.
+  ICING_ASSERT_OK_AND_ASSIGN(
+      std::unique_ptr<PostingListIntegerIndexAccessor> pl_accessor3,
+      PostingListIntegerIndexAccessor::Create(flash_index_storage_.get(),
+                                              serializer_.get()));
+  // Add 2 data.
+  ICING_ASSERT_OK(pl_accessor3->PrependData(data1));
+  ICING_ASSERT_OK(pl_accessor3->PrependData(data2));
+  PostingListAccessor::FinalizeResult result3 =
+      std::move(*pl_accessor3).Finalize();
+  ICING_ASSERT_OK(result3.status);
+  // We should get the same id if the previous one has been freed correctly by
+  // GetAllDataAndFree.
+  EXPECT_THAT(result3.id, Eq(result1.id));
+}
+
+TEST_F(PostingListIntegerIndexAccessorTest, GetAllDataAndFreePostingListChain) {
+  uint32_t block_size = FlashIndexStorage::SelectBlockSize();
+  uint32_t max_posting_list_bytes = IndexBlock::CalculateMaxPostingListBytes(
+      block_size, serializer_->GetDataTypeBytes());
+  uint32_t max_num_data_single_posting_list =
+      max_posting_list_bytes / serializer_->GetDataTypeBytes();
+
+  ICING_ASSERT_OK_AND_ASSIGN(
+      std::unique_ptr<PostingListIntegerIndexAccessor> pl_accessor1,
+      PostingListIntegerIndexAccessor::Create(flash_index_storage_.get(),
+                                              serializer_.get()));
+
+  // Prepend max_num_data_single_posting_list + 1 data.
+  std::vector<IntegerIndexData> data_vec;
+  for (uint32_t i = 0; i < max_num_data_single_posting_list + 1; ++i) {
+    IntegerIndexData data(/*section_id=*/3, static_cast<DocumentId>(i),
+                          /*key=*/i);
+    ICING_ASSERT_OK(pl_accessor1->PrependData(data));
+    data_vec.push_back(data);
+  }
+
+  // This will cause:
+  // - Allocate the first max-sized posting list at block index = 1, storing
+  //   max_num_data_single_posting_list data.
+  // - Allocate the second max-sized posting list at block index = 2, storing 1
+  //   data. Also its next_block_index is 1.
+  // - IOW, we will get 2 -> 1 and result1.id points to 2.
+  PostingListAccessor::FinalizeResult result1 =
+      std::move(*pl_accessor1).Finalize();
+  ICING_ASSERT_OK(result1.status);
+
+  uint32_t first_pl_block_index = kInvalidBlockIndex;
+  {
+    // result1.id points at the second (max-sized) PL, and next_block_index of
+    // the second PL points to the first PL's block. Fetch the first PL's block
+    // index manually.
+    ICING_ASSERT_OK_AND_ASSIGN(
+        PostingListHolder pl_holder,
+        flash_index_storage_->GetPostingList(result1.id));
+    first_pl_block_index = pl_holder.next_block_index;
+  }
+  ASSERT_THAT(first_pl_block_index, Ne(kInvalidBlockIndex));
+
+  // Call GetAllDataAndFree. This will free block 2 and block 1.
+  // Free block list: 1 -> 2 (since free block list is LIFO).
+  ICING_ASSERT_OK_AND_ASSIGN(
+      std::unique_ptr<PostingListIntegerIndexAccessor> pl_accessor2,
+      PostingListIntegerIndexAccessor::CreateFromExisting(
+          flash_index_storage_.get(), serializer_.get(), result1.id));
+  EXPECT_THAT(
+      pl_accessor2->GetAllDataAndFree(),
+      IsOkAndHolds(ElementsAreArray(data_vec.rbegin(), data_vec.rend())));
+  pl_accessor2.reset();
+
+  // Allocate a new posting list with same size again.
+  ICING_ASSERT_OK_AND_ASSIGN(
+      std::unique_ptr<PostingListIntegerIndexAccessor> pl_accessor3,
+      PostingListIntegerIndexAccessor::Create(flash_index_storage_.get(),
+                                              serializer_.get()));
+  // Add same set of data.
+  for (uint32_t i = 0; i < max_num_data_single_posting_list + 1; ++i) {
+    ICING_ASSERT_OK(pl_accessor3->PrependData(data_vec[i]));
+  }
+
+  // This will cause:
+  // - Allocate the first max-sized posting list from the free block list, which
+  //   is block index = 1, storing max_num_data_single_posting_list data.
+  // - Allocate the second max-sized posting list from the next block in free
+  //   block list, which is block index = 2, storing 1 data. Also its
+  //   next_block_index should be 1.
+  PostingListAccessor::FinalizeResult result3 =
+      std::move(*pl_accessor3).Finalize();
+  ICING_ASSERT_OK(result3.status);
+  // We should get the same id if the previous one has been freed correctly by
+  // GetAllDataAndFree.
+  EXPECT_THAT(result3.id, Eq(result1.id));
+  // Also the first PL should be the same if it has been freed correctly by
+  // GetAllDataAndFree. Since it is a max-sized posting list, we just need to
+  // verify the block index.
+  {
+    ICING_ASSERT_OK_AND_ASSIGN(
+        PostingListHolder pl_holder,
+        flash_index_storage_->GetPostingList(result3.id));
+    EXPECT_THAT(pl_holder.next_block_index, Eq(first_pl_block_index));
+  }
+}
+
 }  // namespace
 
 }  // namespace lib
diff --git a/icing/index/numeric/posting-list-integer-index-serializer.h b/icing/index/numeric/posting-list-integer-index-serializer.h
index 9cfdb7a..ea2f2da 100644
--- a/icing/index/numeric/posting-list-integer-index-serializer.h
+++ b/icing/index/numeric/posting-list-integer-index-serializer.h
@@ -111,6 +111,12 @@ class PostingListIntegerIndexSerializer : public PostingListSerializer {
   libtextclassifier3::Status PopFrontData(PostingListUsed* posting_list_used,
                                           uint32_t num_data) const;
 
+  // Helper function to determine if posting list is full.
+  bool IsFull(const PostingListUsed* posting_list_used) const {
+    return GetSpecialData(posting_list_used, /*index=*/0).data().is_valid() &&
+           GetSpecialData(posting_list_used, /*index=*/1).data().is_valid();
+  }
+
  private:
   // Posting list layout formats:
   //
@@ -228,11 +234,6 @@ class PostingListIntegerIndexSerializer : public PostingListSerializer {
   // +-----------------+-----------------+---+--------+-----+--------+--------+
 
   // Helpers to determine what state the posting list is in.
-  bool IsFull(const PostingListUsed* posting_list_used) const {
-    return GetSpecialData(posting_list_used, /*index=*/0).data().is_valid() &&
-           GetSpecialData(posting_list_used, /*index=*/1).data().is_valid();
-  }
-
   bool IsAlmostFull(const PostingListUsed* posting_list_used) const {
     return !GetSpecialData(posting_list_used, /*index=*/0).data().is_valid() &&
            GetSpecialData(posting_list_used, /*index=*/1).data().is_valid();
diff --git a/icing/join/join-processor.cc b/icing/join/join-processor.cc
index ab32850..da0e5d2 100644
--- a/icing/join/join-processor.cc
+++ b/icing/join/join-processor.cc
@@ -27,9 +27,10 @@
 #include "icing/join/qualified-id.h"
 #include "icing/proto/scoring.pb.h"
 #include "icing/proto/search.pb.h"
+#include "icing/schema/joinable-property.h"
 #include "icing/scoring/scored-document-hit.h"
 #include "icing/store/document-id.h"
-#include "icing/util/snippet-helpers.h"
+#include "icing/util/status-macros.h"
 
 namespace icing {
 namespace lib {
@@ -67,34 +68,20 @@ JoinProcessor::GetChildrenFetcher(
   std::unordered_map<DocumentId, std::vector<ScoredDocumentHit>>
       map_joinable_qualified_id;
   for (const ScoredDocumentHit& child : child_scored_document_hits) {
-    std::string property_content = FetchPropertyExpressionValue(
-        child.document_id(), join_spec.child_property_expression());
-
-    // Parse qualified id.
-    libtextclassifier3::StatusOr<QualifiedId> qualified_id_or =
-        QualifiedId::Parse(property_content);
-    if (!qualified_id_or.ok()) {
-      ICING_VLOG(2) << "Skip content with invalid format of QualifiedId";
-      continue;
-    }
-    QualifiedId qualified_id = std::move(qualified_id_or).ValueOrDie();
-
-    // Lookup parent DocumentId.
-    libtextclassifier3::StatusOr<DocumentId> parent_doc_id_or =
-        doc_store_->GetDocumentId(qualified_id.name_space(),
-                                  qualified_id.uri());
-    if (!parent_doc_id_or.ok()) {
-      // Skip the document if getting errors.
+    ICING_ASSIGN_OR_RETURN(
+        DocumentId ref_doc_id,
+        FetchReferencedQualifiedId(child.document_id(),
+                                   join_spec.child_property_expression()));
+    if (ref_doc_id == kInvalidDocumentId) {
       continue;
     }
-    DocumentId parent_doc_id = std::move(parent_doc_id_or).ValueOrDie();
 
     // Since we've already sorted child_scored_document_hits, just simply omit
     // if the map_joinable_qualified_id[parent_doc_id].size() has reached max
     // joined child count.
-    if (map_joinable_qualified_id[parent_doc_id].size() <
+    if (map_joinable_qualified_id[ref_doc_id].size() <
         join_spec.max_joined_child_count()) {
-      map_joinable_qualified_id[parent_doc_id].push_back(child);
+      map_joinable_qualified_id[ref_doc_id].push_back(child);
     }
   }
   return JoinChildrenFetcher(join_spec, std::move(map_joinable_qualified_id));
@@ -127,20 +114,49 @@ JoinProcessor::Join(
   return joined_scored_document_hits;
 }
 
-std::string JoinProcessor::FetchPropertyExpressionValue(
-    const DocumentId& document_id,
-    const std::string& property_expression) const {
-  // TODO(b/256022027): Add caching of document_id -> {expression -> value}
-  libtextclassifier3::StatusOr<DocumentProto> document_or =
-      doc_store_->Get(document_id);
-  if (!document_or.ok()) {
-    // Skip the document if getting errors.
-    return "";
+libtextclassifier3::StatusOr<DocumentId>
+JoinProcessor::FetchReferencedQualifiedId(
+    const DocumentId& document_id, const std::string& property_path) const {
+  std::optional<DocumentFilterData> filter_data =
+      doc_store_->GetAliveDocumentFilterData(document_id);
+  if (!filter_data) {
+    return kInvalidDocumentId;
+  }
+
+  ICING_ASSIGN_OR_RETURN(const JoinablePropertyMetadata* metadata,
+                         schema_store_->GetJoinablePropertyMetadata(
+                             filter_data->schema_type_id(), property_path));
+  if (metadata == nullptr ||
+      metadata->value_type != JoinableConfig::ValueType::QUALIFIED_ID) {
+    // Currently we only support qualified id.
+    return kInvalidDocumentId;
   }
 
-  DocumentProto document = std::move(document_or).ValueOrDie();
+  DocJoinInfo info(document_id, metadata->id);
+  libtextclassifier3::StatusOr<std::string_view> ref_qualified_id_str_or =
+      qualified_id_join_index_->Get(info);
+  if (!ref_qualified_id_str_or.ok()) {
+    if (absl_ports::IsNotFound(ref_qualified_id_str_or.status())) {
+      return kInvalidDocumentId;
+    }
+    return std::move(ref_qualified_id_str_or).status();
+  }
 
-  return std::string(GetString(&document, property_expression));
+  libtextclassifier3::StatusOr<QualifiedId> ref_qualified_id_or =
+      QualifiedId::Parse(std::move(ref_qualified_id_str_or).ValueOrDie());
+  if (!ref_qualified_id_or.ok()) {
+    // This shouldn't happen because we've validated it during indexing and only
+    // put valid qualified id strings into qualified id join index.
+    return kInvalidDocumentId;
+  }
+  QualifiedId qualified_id = std::move(ref_qualified_id_or).ValueOrDie();
+
+  libtextclassifier3::StatusOr<DocumentId> ref_document_id_or =
+      doc_store_->GetDocumentId(qualified_id.name_space(), qualified_id.uri());
+  if (!ref_document_id_or.ok()) {
+    return kInvalidDocumentId;
+  }
+  return std::move(ref_document_id_or).ValueOrDie();
 }
 
 }  // namespace lib
diff --git a/icing/join/join-processor.h b/icing/join/join-processor.h
index 9d5ee11..497787f 100644
--- a/icing/join/join-processor.h
+++ b/icing/join/join-processor.h
@@ -21,7 +21,9 @@
 
 #include "icing/text_classifier/lib3/utils/base/statusor.h"
 #include "icing/join/join-children-fetcher.h"
+#include "icing/join/qualified-id-type-joinable-index.h"
 #include "icing/proto/search.pb.h"
+#include "icing/schema/schema-store.h"
 #include "icing/scoring/scored-document-hit.h"
 #include "icing/store/document-store.h"
 
@@ -32,8 +34,12 @@ class JoinProcessor {
  public:
   static constexpr std::string_view kQualifiedIdExpr = "this.qualifiedId()";
 
-  explicit JoinProcessor(const DocumentStore* doc_store)
-      : doc_store_(doc_store) {}
+  explicit JoinProcessor(
+      const DocumentStore* doc_store, const SchemaStore* schema_store,
+      const QualifiedIdTypeJoinableIndex* qualified_id_join_index)
+      : doc_store_(doc_store),
+        schema_store_(schema_store),
+        qualified_id_join_index_(qualified_id_join_index) {}
 
   // Get a JoinChildrenFetcher used to fetch all children documents by a parent
   // document id.
@@ -52,23 +58,25 @@ class JoinProcessor {
       const JoinChildrenFetcher& join_children_fetcher);
 
  private:
-  // Loads a document and uses a property expression to fetch the value of the
-  // property from the document. The property expression may refer to nested
-  // document properties.
-  // Note: currently we only support single joining, so we use the first element
-  // (index 0) for any repeated values.
+  // Fetches referenced document id of the given document under the given
+  // property path.
   //
   // TODO(b/256022027): validate joinable property (and its upper-level) should
   //                    not have REPEATED cardinality.
   //
   // Returns:
-  //   "" on document load error.
-  //   "" if the property path is not found in the document.
-  std::string FetchPropertyExpressionValue(
-      const DocumentId& document_id,
-      const std::string& property_expression) const;
+  //   - A valid referenced document id on success
+  //   - kInvalidDocumentId if the given document is not found, doesn't have
+  //     qualified id joinable type for the given property_path, or doesn't have
+  //     joinable value (an optional property)
+  //   - Any other QualifiedIdTypeJoinableIndex errors
+  libtextclassifier3::StatusOr<DocumentId> FetchReferencedQualifiedId(
+      const DocumentId& document_id, const std::string& property_path) const;
 
   const DocumentStore* doc_store_;  // Does not own.
+  const SchemaStore* schema_store_;  // Does not own.
+  const QualifiedIdTypeJoinableIndex*
+      qualified_id_join_index_;  // Does not own.
 };
 
 }  // namespace lib
diff --git a/icing/join/join-processor_test.cc b/icing/join/join-processor_test.cc
index 00f2b1c..25d4cfc 100644
--- a/icing/join/join-processor_test.cc
+++ b/icing/join/join-processor_test.cc
@@ -22,6 +22,8 @@
 #include "gtest/gtest.h"
 #include "icing/document-builder.h"
 #include "icing/file/filesystem.h"
+#include "icing/join/qualified-id-joinable-property-indexing-handler.h"
+#include "icing/join/qualified-id-type-joinable-index.h"
 #include "icing/proto/document.pb.h"
 #include "icing/proto/schema.pb.h"
 #include "icing/proto/scoring.pb.h"
@@ -33,7 +35,14 @@
 #include "icing/store/document-id.h"
 #include "icing/testing/common-matchers.h"
 #include "icing/testing/fake-clock.h"
+#include "icing/testing/icu-data-file-helper.h"
+#include "icing/testing/test-data.h"
 #include "icing/testing/tmp-directory.h"
+#include "icing/tokenization/language-segmenter-factory.h"
+#include "icing/tokenization/language-segmenter.h"
+#include "icing/util/status-macros.h"
+#include "icing/util/tokenized-document.h"
+#include "unicode/uloc.h"
 
 namespace icing {
 namespace lib {
@@ -41,16 +50,37 @@ namespace lib {
 namespace {
 
 using ::testing::ElementsAre;
+using ::testing::IsTrue;
 
 class JoinProcessorTest : public ::testing::Test {
  protected:
   void SetUp() override {
     test_dir_ = GetTestTempDir() + "/icing_join_processor_test";
-    filesystem_.CreateDirectoryRecursively(test_dir_.c_str());
+    ASSERT_THAT(filesystem_.CreateDirectoryRecursively(test_dir_.c_str()),
+                IsTrue());
 
+    schema_store_dir_ = test_dir_ + "/schema_store";
+    doc_store_dir_ = test_dir_ + "/doc_store";
+    qualified_id_join_index_dir_ = test_dir_ + "/qualified_id_join_index";
+
+    if (!IsCfStringTokenization() && !IsReverseJniTokenization()) {
+      ICING_ASSERT_OK(
+          // File generated via icu_data_file rule in //icing/BUILD.
+          icu_data_file_helper::SetUpICUDataFile(
+              GetTestFilePath("icing/icu.dat")));
+    }
+
+    language_segmenter_factory::SegmenterOptions options(ULOC_US);
+    ICING_ASSERT_OK_AND_ASSIGN(
+        lang_segmenter_,
+        language_segmenter_factory::Create(std::move(options)));
+
+    ASSERT_THAT(
+        filesystem_.CreateDirectoryRecursively(schema_store_dir_.c_str()),
+        IsTrue());
     ICING_ASSERT_OK_AND_ASSIGN(
         schema_store_,
-        SchemaStore::Create(&filesystem_, test_dir_, &fake_clock_));
+        SchemaStore::Create(&filesystem_, schema_store_dir_, &fake_clock_));
 
     SchemaProto schema =
         SchemaBuilder()
@@ -75,24 +105,51 @@ class JoinProcessorTest : public ::testing::Test {
             .Build();
     ASSERT_THAT(schema_store_->SetSchema(schema), IsOk());
 
+    ASSERT_THAT(filesystem_.CreateDirectoryRecursively(doc_store_dir_.c_str()),
+                IsTrue());
     ICING_ASSERT_OK_AND_ASSIGN(
         DocumentStore::CreateResult create_result,
-        DocumentStore::Create(&filesystem_, test_dir_, &fake_clock_,
+        DocumentStore::Create(&filesystem_, doc_store_dir_, &fake_clock_,
                               schema_store_.get()));
     doc_store_ = std::move(create_result.document_store);
+
+    ICING_ASSERT_OK_AND_ASSIGN(qualified_id_join_index_,
+                               QualifiedIdTypeJoinableIndex::Create(
+                                   filesystem_, qualified_id_join_index_dir_));
   }
 
   void TearDown() override {
+    qualified_id_join_index_.reset();
     doc_store_.reset();
     schema_store_.reset();
+    lang_segmenter_.reset();
     filesystem_.DeleteDirectoryRecursively(test_dir_.c_str());
   }
 
+  libtextclassifier3::StatusOr<DocumentId> PutAndIndexDocument(
+      const DocumentProto& document) {
+    ICING_ASSIGN_OR_RETURN(DocumentId document_id, doc_store_->Put(document));
+    ICING_ASSIGN_OR_RETURN(
+        TokenizedDocument tokenized_document,
+        TokenizedDocument::Create(schema_store_.get(), lang_segmenter_.get(),
+                                  document));
+
+    ICING_ASSIGN_OR_RETURN(
+        std::unique_ptr<QualifiedIdJoinablePropertyIndexingHandler> handler,
+        QualifiedIdJoinablePropertyIndexingHandler::Create(
+            &fake_clock_, qualified_id_join_index_.get()));
+    ICING_RETURN_IF_ERROR(handler->Handle(tokenized_document, document_id,
+                                          /*recovery_mode=*/false,
+                                          /*put_document_stats=*/nullptr));
+    return document_id;
+  }
+
   libtextclassifier3::StatusOr<std::vector<JoinedScoredDocumentHit>> Join(
       const JoinSpecProto& join_spec,
       std::vector<ScoredDocumentHit>&& parent_scored_document_hits,
       std::vector<ScoredDocumentHit>&& child_scored_document_hits) {
-    JoinProcessor join_processor(doc_store_.get());
+    JoinProcessor join_processor(doc_store_.get(), schema_store_.get(),
+                                 qualified_id_join_index_.get());
     ICING_ASSIGN_OR_RETURN(
         JoinChildrenFetcher join_children_fetcher,
         join_processor.GetChildrenFetcher(
@@ -104,8 +161,15 @@ class JoinProcessorTest : public ::testing::Test {
 
   Filesystem filesystem_;
   std::string test_dir_;
+  std::string schema_store_dir_;
+  std::string doc_store_dir_;
+  std::string qualified_id_join_index_dir_;
+
+  std::unique_ptr<LanguageSegmenter> lang_segmenter_;
   std::unique_ptr<SchemaStore> schema_store_;
   std::unique_ptr<DocumentStore> doc_store_;
+  std::unique_ptr<QualifiedIdTypeJoinableIndex> qualified_id_join_index_;
+
   FakeClock fake_clock_;
 };
 
@@ -144,11 +208,16 @@ TEST_F(JoinProcessorTest, JoinByQualifiedId) {
           .AddStringProperty("sender", "pkg$db/namespace#person1")
           .Build();
 
-  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id1, doc_store_->Put(person1));
-  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id2, doc_store_->Put(person2));
-  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id3, doc_store_->Put(email1));
-  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id4, doc_store_->Put(email2));
-  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id5, doc_store_->Put(email3));
+  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id1,
+                             PutAndIndexDocument(person1));
+  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id2,
+                             PutAndIndexDocument(person2));
+  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id3,
+                             PutAndIndexDocument(email1));
+  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id4,
+                             PutAndIndexDocument(email2));
+  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id5,
+                             PutAndIndexDocument(email3));
 
   ScoredDocumentHit scored_doc_hit1(document_id1, kSectionIdMaskNone,
                                     /*score=*/0.0);
@@ -216,9 +285,12 @@ TEST_F(JoinProcessorTest, ShouldIgnoreChildDocumentsWithoutJoiningProperty) {
                              .AddStringProperty("subject", "test subject 2")
                              .Build();
 
-  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id1, doc_store_->Put(person1));
-  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id2, doc_store_->Put(email1));
-  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id3, doc_store_->Put(email2));
+  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id1,
+                             PutAndIndexDocument(person1));
+  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id2,
+                             PutAndIndexDocument(email1));
+  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id3,
+                             PutAndIndexDocument(email2));
 
   ScoredDocumentHit scored_doc_hit1(document_id1, kSectionIdMaskNone,
                                     /*score=*/0.0);
@@ -290,10 +362,14 @@ TEST_F(JoinProcessorTest, ShouldIgnoreChildDocumentsWithInvalidQualifiedId) {
                              R"(pkg$db/namespace\#person1)")  // invalid format
           .Build();
 
-  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id1, doc_store_->Put(person1));
-  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id2, doc_store_->Put(email1));
-  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id3, doc_store_->Put(email2));
-  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id4, doc_store_->Put(email3));
+  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id1,
+                             PutAndIndexDocument(person1));
+  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id2,
+                             PutAndIndexDocument(email1));
+  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id3,
+                             PutAndIndexDocument(email2));
+  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id4,
+                             PutAndIndexDocument(email3));
 
   ScoredDocumentHit scored_doc_hit1(document_id1, kSectionIdMaskNone,
                                     /*score=*/0.0);
@@ -356,9 +432,12 @@ TEST_F(JoinProcessorTest, LeftJoinShouldReturnParentWithoutChildren) {
                              R"(pkg$db/name\#space\\\\#person2)")  // escaped
           .Build();
 
-  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id1, doc_store_->Put(person1));
-  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id2, doc_store_->Put(person2));
-  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id3, doc_store_->Put(email1));
+  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id1,
+                             PutAndIndexDocument(person1));
+  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id2,
+                             PutAndIndexDocument(person2));
+  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id3,
+                             PutAndIndexDocument(email1));
 
   ScoredDocumentHit scored_doc_hit1(document_id1, kSectionIdMaskNone,
                                     /*score=*/0.0);
@@ -430,10 +509,14 @@ TEST_F(JoinProcessorTest, ShouldSortChildDocumentsByRankingStrategy) {
           .AddStringProperty("sender", "pkg$db/namespace#person1")
           .Build();
 
-  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id1, doc_store_->Put(person1));
-  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id2, doc_store_->Put(email1));
-  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id3, doc_store_->Put(email2));
-  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id4, doc_store_->Put(email3));
+  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id1,
+                             PutAndIndexDocument(person1));
+  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id2,
+                             PutAndIndexDocument(email1));
+  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id3,
+                             PutAndIndexDocument(email2));
+  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id4,
+                             PutAndIndexDocument(email3));
 
   ScoredDocumentHit scored_doc_hit1(document_id1, kSectionIdMaskNone,
                                     /*score=*/0.0);
@@ -519,12 +602,18 @@ TEST_F(JoinProcessorTest,
                              R"(pkg$db/name\#space\\\\#person2)")  // escaped
           .Build();
 
-  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id1, doc_store_->Put(person1));
-  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id2, doc_store_->Put(person2));
-  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id3, doc_store_->Put(email1));
-  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id4, doc_store_->Put(email2));
-  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id5, doc_store_->Put(email3));
-  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id6, doc_store_->Put(email4));
+  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id1,
+                             PutAndIndexDocument(person1));
+  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id2,
+                             PutAndIndexDocument(person2));
+  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id3,
+                             PutAndIndexDocument(email1));
+  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id4,
+                             PutAndIndexDocument(email2));
+  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id5,
+                             PutAndIndexDocument(email3));
+  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id6,
+                             PutAndIndexDocument(email4));
 
   ScoredDocumentHit scored_doc_hit1(document_id1, kSectionIdMaskNone,
                                     /*score=*/0.0);
@@ -587,7 +676,8 @@ TEST_F(JoinProcessorTest, ShouldAllowSelfJoining) {
           .AddStringProperty("sender", "pkg$db/namespace#email1")
           .Build();
 
-  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id1, doc_store_->Put(email1));
+  ICING_ASSERT_OK_AND_ASSIGN(DocumentId document_id1,
+                             PutAndIndexDocument(email1));
 
   ScoredDocumentHit scored_doc_hit1(document_id1, kSectionIdMaskNone,
                                     /*score=*/0.0);
diff --git a/icing/join/qualified-id-joinable-property-indexing-handler.cc b/icing/join/qualified-id-joinable-property-indexing-handler.cc
new file mode 100644
index 0000000..0b28444
--- /dev/null
+++ b/icing/join/qualified-id-joinable-property-indexing-handler.cc
@@ -0,0 +1,96 @@
+// Copyright (C) 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "icing/join/qualified-id-joinable-property-indexing-handler.h"
+
+#include <memory>
+#include <string_view>
+
+#include "icing/text_classifier/lib3/utils/base/status.h"
+#include "icing/absl_ports/canonical_errors.h"
+#include "icing/join/doc-join-info.h"
+#include "icing/join/qualified-id-type-joinable-index.h"
+#include "icing/join/qualified-id.h"
+#include "icing/legacy/core/icing-string-util.h"
+#include "icing/proto/logging.pb.h"
+#include "icing/store/document-id.h"
+#include "icing/util/logging.h"
+#include "icing/util/tokenized-document.h"
+
+namespace icing {
+namespace lib {
+
+/* static */ libtextclassifier3::StatusOr<
+    std::unique_ptr<QualifiedIdJoinablePropertyIndexingHandler>>
+QualifiedIdJoinablePropertyIndexingHandler::Create(
+    const Clock* clock, QualifiedIdTypeJoinableIndex* qualified_id_join_index) {
+  ICING_RETURN_ERROR_IF_NULL(clock);
+  ICING_RETURN_ERROR_IF_NULL(qualified_id_join_index);
+
+  return std::unique_ptr<QualifiedIdJoinablePropertyIndexingHandler>(
+      new QualifiedIdJoinablePropertyIndexingHandler(clock,
+                                                     qualified_id_join_index));
+}
+
+libtextclassifier3::Status QualifiedIdJoinablePropertyIndexingHandler::Handle(
+    const TokenizedDocument& tokenized_document, DocumentId document_id,
+    bool recovery_mode, PutDocumentStatsProto* put_document_stats) {
+  // TODO(b/263890397): set qualified id join index processing latency and other
+  // stats.
+
+  if (qualified_id_join_index_.last_added_document_id() != kInvalidDocumentId &&
+      document_id <= qualified_id_join_index_.last_added_document_id()) {
+    if (recovery_mode) {
+      // Skip the document if document_id <= last_added_document_id in recovery
+      // mode without returning an error.
+      return libtextclassifier3::Status::OK;
+    }
+    return absl_ports::InvalidArgumentError(IcingStringUtil::StringPrintf(
+        "DocumentId %d must be greater than last added document_id %d",
+        document_id, qualified_id_join_index_.last_added_document_id()));
+  }
+  qualified_id_join_index_.set_last_added_document_id(document_id);
+
+  for (const JoinableProperty<std::string_view>& qualified_id_property :
+       tokenized_document.qualified_id_join_properties()) {
+    if (qualified_id_property.values.empty()) {
+      continue;
+    }
+
+    DocJoinInfo info(document_id, qualified_id_property.metadata.id);
+    // Currently we only support single (non-repeated) joinable value under a
+    // property.
+    std::string_view ref_qualified_id_str = qualified_id_property.values[0];
+
+    // Attempt to parse qualified id string to make sure the format is correct.
+    if (!QualifiedId::Parse(ref_qualified_id_str).ok()) {
+      // Skip incorrect format of qualified id string to save disk space.
+      continue;
+    }
+
+    libtextclassifier3::Status status =
+        qualified_id_join_index_.Put(info, ref_qualified_id_str);
+    if (!status.ok()) {
+      ICING_LOG(WARNING)
+          << "Failed to add data into qualified id join index due to: "
+          << status.error_message();
+      return status;
+    }
+  }
+
+  return libtextclassifier3::Status::OK;
+}
+
+}  // namespace lib
+}  // namespace icing
diff --git a/icing/join/qualified-id-joinable-property-indexing-handler.h b/icing/join/qualified-id-joinable-property-indexing-handler.h
new file mode 100644
index 0000000..111526e
--- /dev/null
+++ b/icing/join/qualified-id-joinable-property-indexing-handler.h
@@ -0,0 +1,71 @@
+// Copyright (C) 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ICING_JOIN_QUALIFIED_ID_JOINABLE_PROPERTY_INDEXING_HANDLER_H_
+#define ICING_JOIN_QUALIFIED_ID_JOINABLE_PROPERTY_INDEXING_HANDLER_H_
+
+#include "icing/text_classifier/lib3/utils/base/status.h"
+#include "icing/index/data-indexing-handler.h"
+#include "icing/join/qualified-id-type-joinable-index.h"
+#include "icing/proto/logging.pb.h"
+#include "icing/store/document-id.h"
+#include "icing/util/clock.h"
+#include "icing/util/tokenized-document.h"
+
+namespace icing {
+namespace lib {
+
+class QualifiedIdJoinablePropertyIndexingHandler : public DataIndexingHandler {
+ public:
+  // Creates a QualifiedIdJoinablePropertyIndexingHandler instance which does
+  // not take ownership of any input components. All pointers must refer to
+  // valid objects that outlive the created
+  // QualifiedIdJoinablePropertyIndexingHandler instance.
+  //
+  // Returns:
+  //   - A QualifiedIdJoinablePropertyIndexingHandler instance on success
+  //   - FAILED_PRECONDITION_ERROR if any of the input pointer is null
+  static libtextclassifier3::StatusOr<
+      std::unique_ptr<QualifiedIdJoinablePropertyIndexingHandler>>
+  Create(const Clock* clock,
+         QualifiedIdTypeJoinableIndex* qualified_id_join_index);
+
+  ~QualifiedIdJoinablePropertyIndexingHandler() override = default;
+
+  // Handles the joinable qualified id data indexing process: add data into the
+  // qualified id type joinable cache.
+  //
+  /// Returns:
+  //   - OK on success
+  //   - INVALID_ARGUMENT_ERROR if document_id is less than or equal to the
+  //     document_id of a previously indexed document in non recovery mode.
+  //   - INTERNAL_ERROR if any other errors occur.
+  //   - Any QualifiedIdTypeJoinableIndex errors.
+  libtextclassifier3::Status Handle(
+      const TokenizedDocument& tokenized_document, DocumentId document_id,
+      bool recovery_mode, PutDocumentStatsProto* put_document_stats) override;
+
+ private:
+  explicit QualifiedIdJoinablePropertyIndexingHandler(
+      const Clock* clock, QualifiedIdTypeJoinableIndex* qualified_id_join_index)
+      : DataIndexingHandler(clock),
+        qualified_id_join_index_(*qualified_id_join_index) {}
+
+  QualifiedIdTypeJoinableIndex& qualified_id_join_index_;  // Does not own.
+};
+
+}  // namespace lib
+}  // namespace icing
+
+#endif  // ICING_JOIN_QUALIFIED_ID_JOINABLE_PROPERTY_INDEXING_HANDLER_H_
diff --git a/icing/join/qualified-id-joinable-property-indexing-handler_test.cc b/icing/join/qualified-id-joinable-property-indexing-handler_test.cc
new file mode 100644
index 0000000..aa5624c
--- /dev/null
+++ b/icing/join/qualified-id-joinable-property-indexing-handler_test.cc
@@ -0,0 +1,332 @@
+// Copyright (C) 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "icing/join/qualified-id-joinable-property-indexing-handler.h"
+
+#include <memory>
+#include <string>
+#include <string_view>
+
+#include "icing/text_classifier/lib3/utils/base/status.h"
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include "icing/document-builder.h"
+#include "icing/file/filesystem.h"
+#include "icing/join/qualified-id-type-joinable-index.h"
+#include "icing/join/qualified-id.h"
+#include "icing/portable/platform.h"
+#include "icing/proto/document.pb.h"
+#include "icing/proto/schema.pb.h"
+#include "icing/schema-builder.h"
+#include "icing/schema/joinable-property.h"
+#include "icing/schema/schema-store.h"
+#include "icing/store/document-id.h"
+#include "icing/testing/common-matchers.h"
+#include "icing/testing/fake-clock.h"
+#include "icing/testing/icu-data-file-helper.h"
+#include "icing/testing/test-data.h"
+#include "icing/testing/tmp-directory.h"
+#include "icing/tokenization/language-segmenter-factory.h"
+#include "icing/tokenization/language-segmenter.h"
+#include "icing/util/tokenized-document.h"
+#include "unicode/uloc.h"
+
+namespace icing {
+namespace lib {
+
+namespace {
+
+using ::testing::Eq;
+using ::testing::IsEmpty;
+using ::testing::IsTrue;
+
+// Schema type for referenced documents: ReferencedType
+static constexpr std::string_view kReferencedType = "ReferencedType";
+static constexpr std::string_view kPropertyName = "name";
+
+// Joinable properties and joinable property id. Joinable property id is
+// determined by the lexicographical order of joinable property path.
+// Schema type with joinable property: FakeType
+static constexpr std::string_view kFakeType = "FakeType";
+static constexpr std::string_view kPropertyQualifiedId = "qualifiedId";
+
+static constexpr JoinablePropertyId kQualifiedIdJoinablePropertyId = 0;
+
+// Schema type with nested joinable properties: NestedType
+static constexpr std::string_view kNestedType = "NestedType";
+static constexpr std::string_view kPropertyNestedDoc = "nested";
+static constexpr std::string_view kPropertyQualifiedId2 = "qualifiedId2";
+
+static constexpr JoinablePropertyId kNestedQualifiedIdJoinablePropertyId = 0;
+static constexpr JoinablePropertyId kQualifiedId2JoinablePropertyId = 1;
+
+static constexpr DocumentId kDefaultDocumentId = 3;
+
+class QualifiedIdJoinablePropertyIndexingHandlerTest : public ::testing::Test {
+ protected:
+  void SetUp() override {
+    if (!IsCfStringTokenization() && !IsReverseJniTokenization()) {
+      ICING_ASSERT_OK(
+          // File generated via icu_data_file rule in //icing/BUILD.
+          icu_data_file_helper::SetUpICUDataFile(
+              GetTestFilePath("icing/icu.dat")));
+    }
+
+    base_dir_ = GetTestTempDir() + "/icing_test";
+    ASSERT_THAT(filesystem_.CreateDirectoryRecursively(base_dir_.c_str()),
+                IsTrue());
+
+    qualified_id_join_index_dir_ = base_dir_ + "/qualified_id_join_index";
+    schema_store_dir_ = base_dir_ + "/schema_store";
+
+    ICING_ASSERT_OK_AND_ASSIGN(qualified_id_join_index_,
+                               QualifiedIdTypeJoinableIndex::Create(
+                                   filesystem_, qualified_id_join_index_dir_));
+
+    language_segmenter_factory::SegmenterOptions segmenter_options(ULOC_US);
+    ICING_ASSERT_OK_AND_ASSIGN(
+        lang_segmenter_,
+        language_segmenter_factory::Create(std::move(segmenter_options)));
+
+    ASSERT_THAT(
+        filesystem_.CreateDirectoryRecursively(schema_store_dir_.c_str()),
+        IsTrue());
+    ICING_ASSERT_OK_AND_ASSIGN(
+        schema_store_,
+        SchemaStore::Create(&filesystem_, schema_store_dir_, &fake_clock_));
+    SchemaProto schema =
+        SchemaBuilder()
+            .AddType(
+                SchemaTypeConfigBuilder()
+                    .SetType(kReferencedType)
+                    .AddProperty(PropertyConfigBuilder()
+                                     .SetName(kPropertyName)
+                                     .SetDataTypeString(TERM_MATCH_EXACT,
+                                                        TOKENIZER_PLAIN)
+                                     .SetCardinality(CARDINALITY_OPTIONAL)))
+            .AddType(SchemaTypeConfigBuilder().SetType(kFakeType).AddProperty(
+                PropertyConfigBuilder()
+                    .SetName(kPropertyQualifiedId)
+                    .SetDataTypeJoinableString(JOINABLE_VALUE_TYPE_QUALIFIED_ID)
+                    .SetCardinality(CARDINALITY_OPTIONAL)))
+            .AddType(
+                SchemaTypeConfigBuilder()
+                    .SetType(kNestedType)
+                    .AddProperty(
+                        PropertyConfigBuilder()
+                            .SetName(kPropertyNestedDoc)
+                            .SetDataTypeDocument(
+                                kFakeType, /*index_nested_properties=*/true)
+                            .SetCardinality(CARDINALITY_OPTIONAL))
+                    .AddProperty(PropertyConfigBuilder()
+                                     .SetName(kPropertyQualifiedId2)
+                                     .SetDataTypeJoinableString(
+                                         JOINABLE_VALUE_TYPE_QUALIFIED_ID)
+                                     .SetCardinality(CARDINALITY_OPTIONAL)))
+            .Build();
+    ICING_ASSERT_OK(schema_store_->SetSchema(schema));
+  }
+
+  void TearDown() override {
+    schema_store_.reset();
+    lang_segmenter_.reset();
+    qualified_id_join_index_.reset();
+
+    filesystem_.DeleteDirectoryRecursively(base_dir_.c_str());
+  }
+
+  Filesystem filesystem_;
+  FakeClock fake_clock_;
+  std::string base_dir_;
+  std::string qualified_id_join_index_dir_;
+  std::string schema_store_dir_;
+
+  std::unique_ptr<QualifiedIdTypeJoinableIndex> qualified_id_join_index_;
+  std::unique_ptr<LanguageSegmenter> lang_segmenter_;
+  std::unique_ptr<SchemaStore> schema_store_;
+};
+
+TEST_F(QualifiedIdJoinablePropertyIndexingHandlerTest,
+       CreationWithNullPointerShouldFail) {
+  EXPECT_THAT(QualifiedIdJoinablePropertyIndexingHandler::Create(
+                  /*clock=*/nullptr, qualified_id_join_index_.get()),
+              StatusIs(libtextclassifier3::StatusCode::FAILED_PRECONDITION));
+
+  EXPECT_THAT(QualifiedIdJoinablePropertyIndexingHandler::Create(
+                  &fake_clock_, /*qualified_id_join_index=*/nullptr),
+              StatusIs(libtextclassifier3::StatusCode::FAILED_PRECONDITION));
+}
+
+TEST_F(QualifiedIdJoinablePropertyIndexingHandlerTest, HandleJoinableProperty) {
+  DocumentProto referenced_document =
+      DocumentBuilder()
+          .SetKey("pkg$db/ns", "ref_type/1")
+          .SetSchema(std::string(kReferencedType))
+          .AddStringProperty(std::string(kPropertyName), "one")
+          .Build();
+
+  DocumentProto document =
+      DocumentBuilder()
+          .SetKey("icing", "fake_type/1")
+          .SetSchema(std::string(kFakeType))
+          .AddStringProperty(std::string(kPropertyQualifiedId),
+                             "pkg$db/ns#ref_type/1")
+          .Build();
+  ICING_ASSERT_OK_AND_ASSIGN(
+      TokenizedDocument tokenized_document,
+      TokenizedDocument::Create(schema_store_.get(), lang_segmenter_.get(),
+                                document));
+
+  // Handle document.
+  ICING_ASSERT_OK_AND_ASSIGN(
+      std::unique_ptr<QualifiedIdJoinablePropertyIndexingHandler> handler,
+      QualifiedIdJoinablePropertyIndexingHandler::Create(
+          &fake_clock_, qualified_id_join_index_.get()));
+  EXPECT_THAT(
+      handler->Handle(tokenized_document, kDefaultDocumentId,
+                      /*recovery_mode=*/false, /*put_document_stats=*/nullptr),
+      StatusIs(libtextclassifier3::StatusCode::OK));
+
+  EXPECT_THAT(qualified_id_join_index_->last_added_document_id(),
+              Eq(kDefaultDocumentId));
+  EXPECT_THAT(qualified_id_join_index_->Get(DocJoinInfo(
+                  kDefaultDocumentId, kQualifiedIdJoinablePropertyId)),
+              IsOkAndHolds("pkg$db/ns#ref_type/1"));
+}
+
+TEST_F(QualifiedIdJoinablePropertyIndexingHandlerTest,
+       HandleNestedJoinableProperty) {
+  DocumentProto referenced_document1 =
+      DocumentBuilder()
+          .SetKey("pkg$db/ns", "ref_type/1")
+          .SetSchema(std::string(kReferencedType))
+          .AddStringProperty(std::string(kPropertyName), "one")
+          .Build();
+  DocumentProto referenced_document2 =
+      DocumentBuilder()
+          .SetKey("pkg$db/ns", "ref_type/2")
+          .SetSchema(std::string(kReferencedType))
+          .AddStringProperty(std::string(kPropertyName), "two")
+          .Build();
+
+  DocumentProto nested_document =
+      DocumentBuilder()
+          .SetKey("pkg$db/ns", "nested_type/1")
+          .SetSchema(std::string(kNestedType))
+          .AddDocumentProperty(
+              std::string(kPropertyNestedDoc),
+              DocumentBuilder()
+                  .SetKey("pkg$db/ns", "nested_fake_type/1")
+                  .SetSchema(std::string(kFakeType))
+                  .AddStringProperty(std::string(kPropertyQualifiedId),
+                                     "pkg$db/ns#ref_type/2")
+                  .Build())
+          .AddStringProperty(std::string(kPropertyQualifiedId2),
+                             "pkg$db/ns#ref_type/1")
+          .Build();
+  ICING_ASSERT_OK_AND_ASSIGN(
+      TokenizedDocument tokenized_document,
+      TokenizedDocument::Create(schema_store_.get(), lang_segmenter_.get(),
+                                nested_document));
+
+  // Handle nested_document.
+  ICING_ASSERT_OK_AND_ASSIGN(
+      std::unique_ptr<QualifiedIdJoinablePropertyIndexingHandler> handler,
+      QualifiedIdJoinablePropertyIndexingHandler::Create(
+          &fake_clock_, qualified_id_join_index_.get()));
+  EXPECT_THAT(handler->Handle(tokenized_document, kDefaultDocumentId,
+                              /*recovery_mode=*/false,
+                              /*put_document_stats=*/nullptr),
+              StatusIs(libtextclassifier3::StatusCode::OK));
+
+  EXPECT_THAT(qualified_id_join_index_->last_added_document_id(),
+              Eq(kDefaultDocumentId));
+  EXPECT_THAT(qualified_id_join_index_->Get(DocJoinInfo(
+                  kDefaultDocumentId, kNestedQualifiedIdJoinablePropertyId)),
+              IsOkAndHolds("pkg$db/ns#ref_type/2"));
+  EXPECT_THAT(qualified_id_join_index_->Get(DocJoinInfo(
+                  kDefaultDocumentId, kQualifiedId2JoinablePropertyId)),
+              IsOkAndHolds("pkg$db/ns#ref_type/1"));
+}
+
+TEST_F(QualifiedIdJoinablePropertyIndexingHandlerTest,
+       HandleShouldSkipInvalidFormatQualifiedId) {
+  static constexpr std::string_view kInvalidFormatQualifiedId =
+      "invalid_format_qualified_id";
+  ASSERT_THAT(QualifiedId::Parse(kInvalidFormatQualifiedId),
+              StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
+
+  DocumentProto document =
+      DocumentBuilder()
+          .SetKey("icing", "fake_type/1")
+          .SetSchema(std::string(kFakeType))
+          .AddStringProperty(std::string(kPropertyQualifiedId),
+                             std::string(kInvalidFormatQualifiedId))
+          .Build();
+  ICING_ASSERT_OK_AND_ASSIGN(
+      TokenizedDocument tokenized_document,
+      TokenizedDocument::Create(schema_store_.get(), lang_segmenter_.get(),
+                                document));
+
+  // Handle document. Handle() should ignore invalid format qualified id.
+  ICING_ASSERT_OK_AND_ASSIGN(
+      std::unique_ptr<QualifiedIdJoinablePropertyIndexingHandler> handler,
+      QualifiedIdJoinablePropertyIndexingHandler::Create(
+          &fake_clock_, qualified_id_join_index_.get()));
+  EXPECT_THAT(
+      handler->Handle(tokenized_document, kDefaultDocumentId,
+                      /*recovery_mode=*/false, /*put_document_stats=*/nullptr),
+      StatusIs(libtextclassifier3::StatusCode::OK));
+
+  EXPECT_THAT(qualified_id_join_index_->last_added_document_id(),
+              Eq(kDefaultDocumentId));
+  EXPECT_THAT(qualified_id_join_index_->Get(DocJoinInfo(
+                  kDefaultDocumentId, kQualifiedIdJoinablePropertyId)),
+              StatusIs(libtextclassifier3::StatusCode::NOT_FOUND));
+}
+
+TEST_F(QualifiedIdJoinablePropertyIndexingHandlerTest,
+       HandleShouldSkipEmptyQualifiedId) {
+  // Create a document without any qualified id.
+  DocumentProto document = DocumentBuilder()
+                               .SetKey("icing", "fake_type/1")
+                               .SetSchema(std::string(kFakeType))
+                               .Build();
+  ICING_ASSERT_OK_AND_ASSIGN(
+      TokenizedDocument tokenized_document,
+      TokenizedDocument::Create(schema_store_.get(), lang_segmenter_.get(),
+                                document));
+  ASSERT_THAT(tokenized_document.qualified_id_join_properties(), IsEmpty());
+
+  // Handle document. Handle() should ignore invalid format qualified id.
+  ICING_ASSERT_OK_AND_ASSIGN(
+      std::unique_ptr<QualifiedIdJoinablePropertyIndexingHandler> handler,
+      QualifiedIdJoinablePropertyIndexingHandler::Create(
+          &fake_clock_, qualified_id_join_index_.get()));
+  EXPECT_THAT(
+      handler->Handle(tokenized_document, kDefaultDocumentId,
+                      /*recovery_mode=*/false, /*put_document_stats=*/nullptr),
+      StatusIs(libtextclassifier3::StatusCode::OK));
+
+  EXPECT_THAT(qualified_id_join_index_->last_added_document_id(),
+              Eq(kDefaultDocumentId));
+  EXPECT_THAT(qualified_id_join_index_->Get(DocJoinInfo(
+                  kDefaultDocumentId, kQualifiedIdJoinablePropertyId)),
+              StatusIs(libtextclassifier3::StatusCode::NOT_FOUND));
+}
+
+}  // namespace
+
+}  // namespace lib
+}  // namespace icing
diff --git a/icing/join/qualified-id-type-joinable-index.cc b/icing/join/qualified-id-type-joinable-index.cc
index 231e78a..9c25e62 100644
--- a/icing/join/qualified-id-type-joinable-index.cc
+++ b/icing/join/qualified-id-type-joinable-index.cc
@@ -14,6 +14,7 @@
 
 #include "icing/join/qualified-id-type-joinable-index.h"
 
+#include <cstring>
 #include <memory>
 #include <string>
 #include <string_view>
@@ -24,7 +25,9 @@
 #include "icing/absl_ports/canonical_errors.h"
 #include "icing/absl_ports/str_cat.h"
 #include "icing/file/destructible-directory.h"
+#include "icing/file/file-backed-vector.h"
 #include "icing/file/filesystem.h"
+#include "icing/file/memory-mapped-file.h"
 #include "icing/join/doc-join-info.h"
 #include "icing/store/document-id.h"
 #include "icing/store/key-mapper.h"
@@ -49,13 +52,15 @@ DocumentId GetNewDocumentId(
 }
 
 std::string GetMetadataFilePath(std::string_view working_path) {
-  return absl_ports::StrCat(working_path, "/",
-                            QualifiedIdTypeJoinableIndex::kFilePrefix, ".m");
+  return absl_ports::StrCat(working_path, "/metadata");
 }
 
-std::string GetDocumentToQualifiedIdMapperPath(std::string_view working_path) {
-  return absl_ports::StrCat(
-      working_path, "/", QualifiedIdTypeJoinableIndex::kFilePrefix, "_mapper");
+std::string GetDocJoinInfoMapperPath(std::string_view working_path) {
+  return absl_ports::StrCat(working_path, "/doc_join_info_mapper");
+}
+
+std::string GetQualifiedIdStoragePath(std::string_view working_path) {
+  return absl_ports::StrCat(working_path, "/qualified_id_storage");
 }
 
 }  // namespace
@@ -66,9 +71,12 @@ QualifiedIdTypeJoinableIndex::Create(const Filesystem& filesystem,
                                      std::string working_path) {
   if (!filesystem.FileExists(GetMetadataFilePath(working_path).c_str()) ||
       !filesystem.DirectoryExists(
-          GetDocumentToQualifiedIdMapperPath(working_path).c_str())) {
+          GetDocJoinInfoMapperPath(working_path).c_str()) ||
+      !filesystem.FileExists(GetQualifiedIdStoragePath(working_path).c_str())) {
     // Discard working_path if any file/directory is missing, and reinitialize.
-    ICING_RETURN_IF_ERROR(Discard(filesystem, working_path));
+    if (filesystem.DirectoryExists(working_path.c_str())) {
+      ICING_RETURN_IF_ERROR(Discard(filesystem, working_path));
+    }
     return InitializeNewFiles(filesystem, std::move(working_path));
   }
   return InitializeExistingFiles(filesystem, std::move(working_path));
@@ -83,29 +91,44 @@ QualifiedIdTypeJoinableIndex::~QualifiedIdTypeJoinableIndex() {
 }
 
 libtextclassifier3::Status QualifiedIdTypeJoinableIndex::Put(
-    const DocJoinInfo& doc_join_info, DocumentId ref_document_id) {
+    const DocJoinInfo& doc_join_info, std::string_view ref_qualified_id_str) {
   if (!doc_join_info.is_valid()) {
     return absl_ports::InvalidArgumentError(
         "Cannot put data for an invalid DocJoinInfo");
   }
 
-  ICING_RETURN_IF_ERROR(document_to_qualified_id_mapper_->Put(
-      encode_util::EncodeIntToCString(doc_join_info.value()), ref_document_id));
+  int32_t qualified_id_index = qualified_id_storage_->num_elements();
+  ICING_ASSIGN_OR_RETURN(
+      FileBackedVector<char>::MutableArrayView mutable_arr,
+      qualified_id_storage_->Allocate(ref_qualified_id_str.size() + 1));
+  mutable_arr.SetArray(/*idx=*/0, ref_qualified_id_str.data(),
+                       ref_qualified_id_str.size());
+  mutable_arr.SetArray(/*idx=*/ref_qualified_id_str.size(), /*arr=*/"\0",
+                       /*arr_len=*/1);
+
+  ICING_RETURN_IF_ERROR(doc_join_info_mapper_->Put(
+      encode_util::EncodeIntToCString(doc_join_info.value()),
+      qualified_id_index));
 
   // TODO(b/268521214): add data into delete propagation storage
 
   return libtextclassifier3::Status::OK;
 }
 
-libtextclassifier3::StatusOr<DocumentId> QualifiedIdTypeJoinableIndex::Get(
-    const DocJoinInfo& doc_join_info) const {
+libtextclassifier3::StatusOr<std::string_view>
+QualifiedIdTypeJoinableIndex::Get(const DocJoinInfo& doc_join_info) const {
   if (!doc_join_info.is_valid()) {
     return absl_ports::InvalidArgumentError(
         "Cannot get data for an invalid DocJoinInfo");
   }
 
-  return document_to_qualified_id_mapper_->Get(
-      encode_util::EncodeIntToCString(doc_join_info.value()));
+  ICING_ASSIGN_OR_RETURN(
+      int32_t qualified_id_index,
+      doc_join_info_mapper_->Get(
+          encode_util::EncodeIntToCString(doc_join_info.value())));
+
+  const char* data = qualified_id_storage_->array() + qualified_id_index;
+  return std::string_view(data, strlen(data));
 }
 
 libtextclassifier3::Status QualifiedIdTypeJoinableIndex::Optimize(
@@ -137,7 +160,8 @@ libtextclassifier3::Status QualifiedIdTypeJoinableIndex::Optimize(
 
   // Destruct current index's storage instances to safely swap directories.
   // TODO(b/268521214): handle delete propagation storage
-  document_to_qualified_id_mapper_.reset();
+  doc_join_info_mapper_.reset();
+  qualified_id_storage_.reset();
 
   if (!filesystem_.SwapFiles(temp_working_path_ddir.dir().c_str(),
                              working_path_.c_str())) {
@@ -153,24 +177,37 @@ libtextclassifier3::Status QualifiedIdTypeJoinableIndex::Optimize(
     return absl_ports::InternalError("Fail to read metadata file");
   }
   ICING_ASSIGN_OR_RETURN(
-      document_to_qualified_id_mapper_,
-      PersistentHashMapKeyMapper<DocumentId>::Create(
-          filesystem_, GetDocumentToQualifiedIdMapperPath(working_path_)));
+      doc_join_info_mapper_,
+      PersistentHashMapKeyMapper<int32_t>::Create(
+          filesystem_, GetDocJoinInfoMapperPath(working_path_)));
+
+  ICING_ASSIGN_OR_RETURN(
+      qualified_id_storage_,
+      FileBackedVector<char>::Create(
+          filesystem_, GetQualifiedIdStoragePath(working_path_),
+          MemoryMappedFile::Strategy::READ_WRITE_AUTO_SYNC,
+          FileBackedVector<char>::kMaxFileSize,
+          /*pre_mapping_mmap_size=*/1024 * 1024));
 
   return libtextclassifier3::Status::OK;
 }
 
 libtextclassifier3::Status QualifiedIdTypeJoinableIndex::Clear() {
-  document_to_qualified_id_mapper_.reset();
-  // Discard and reinitialize document to qualified id mapper.
-  std::string document_to_qualified_id_mapper_path =
-      GetDocumentToQualifiedIdMapperPath(working_path_);
-  ICING_RETURN_IF_ERROR(PersistentHashMapKeyMapper<DocumentId>::Delete(
-      filesystem_, document_to_qualified_id_mapper_path));
+  doc_join_info_mapper_.reset();
+  // Discard and reinitialize doc join info mapper.
+  std::string doc_join_info_mapper_path =
+      GetDocJoinInfoMapperPath(working_path_);
+  ICING_RETURN_IF_ERROR(PersistentHashMapKeyMapper<int32_t>::Delete(
+      filesystem_, doc_join_info_mapper_path));
   ICING_ASSIGN_OR_RETURN(
-      document_to_qualified_id_mapper_,
-      PersistentHashMapKeyMapper<DocumentId>::Create(
-          filesystem_, std::move(document_to_qualified_id_mapper_path)));
+      doc_join_info_mapper_,
+      PersistentHashMapKeyMapper<int32_t>::Create(
+          filesystem_, std::move(doc_join_info_mapper_path)));
+
+  // Clear qualified_id_storage_.
+  if (qualified_id_storage_->num_elements() > 0) {
+    ICING_RETURN_IF_ERROR(qualified_id_storage_->TruncateTo(0));
+  }
 
   // TODO(b/268521214): clear delete propagation storage
 
@@ -188,26 +225,34 @@ QualifiedIdTypeJoinableIndex::InitializeNewFiles(const Filesystem& filesystem,
         absl_ports::StrCat("Failed to create directory: ", working_path));
   }
 
-  // Initialize document_to_qualified_id_mapper
+  // Initialize doc_join_info_mapper
   // TODO(b/263890397): decide PersistentHashMapKeyMapper size
   ICING_ASSIGN_OR_RETURN(
-      std::unique_ptr<KeyMapper<DocumentId>> document_to_qualified_id_mapper,
-      PersistentHashMapKeyMapper<DocumentId>::Create(
-          filesystem, GetDocumentToQualifiedIdMapperPath(working_path)));
+      std::unique_ptr<KeyMapper<int32_t>> doc_join_info_mapper,
+      PersistentHashMapKeyMapper<int32_t>::Create(
+          filesystem, GetDocJoinInfoMapperPath(working_path)));
+
+  // Initialize qualified_id_storage
+  ICING_ASSIGN_OR_RETURN(
+      std::unique_ptr<FileBackedVector<char>> qualified_id_storage,
+      FileBackedVector<char>::Create(
+          filesystem, GetQualifiedIdStoragePath(working_path),
+          MemoryMappedFile::Strategy::READ_WRITE_AUTO_SYNC,
+          FileBackedVector<char>::kMaxFileSize,
+          /*pre_mapping_mmap_size=*/1024 * 1024));
 
   // Create instance.
   auto new_index = std::unique_ptr<QualifiedIdTypeJoinableIndex>(
       new QualifiedIdTypeJoinableIndex(
           filesystem, std::move(working_path),
           /*metadata_buffer=*/std::make_unique<uint8_t[]>(kMetadataFileSize),
-          std::move(document_to_qualified_id_mapper)));
+          std::move(doc_join_info_mapper), std::move(qualified_id_storage)));
   // Initialize info content.
   new_index->info().magic = Info::kMagic;
   new_index->info().last_added_document_id = kInvalidDocumentId;
   // Initialize new PersistentStorage. The initial checksums will be computed
-  // and set via InitializeNewStorage. Also write them into disk as well.
+  // and set via InitializeNewStorage.
   ICING_RETURN_IF_ERROR(new_index->InitializeNewStorage());
-  ICING_RETURN_IF_ERROR(new_index->PersistMetadataToDisk());
 
   return new_index;
 }
@@ -224,17 +269,26 @@ QualifiedIdTypeJoinableIndex::InitializeExistingFiles(
     return absl_ports::InternalError("Fail to read metadata file");
   }
 
-  // Initialize document_to_qualified_id_mapper
+  // Initialize doc_join_info_mapper
   ICING_ASSIGN_OR_RETURN(
-      std::unique_ptr<KeyMapper<DocumentId>> document_to_qualified_id_mapper,
-      PersistentHashMapKeyMapper<DocumentId>::Create(
-          filesystem, GetDocumentToQualifiedIdMapperPath(working_path)));
+      std::unique_ptr<KeyMapper<int32_t>> doc_join_info_mapper,
+      PersistentHashMapKeyMapper<int32_t>::Create(
+          filesystem, GetDocJoinInfoMapperPath(working_path)));
+
+  // Initialize qualified_id_storage
+  ICING_ASSIGN_OR_RETURN(
+      std::unique_ptr<FileBackedVector<char>> qualified_id_storage,
+      FileBackedVector<char>::Create(
+          filesystem, GetQualifiedIdStoragePath(working_path),
+          MemoryMappedFile::Strategy::READ_WRITE_AUTO_SYNC,
+          FileBackedVector<char>::kMaxFileSize,
+          /*pre_mapping_mmap_size=*/1024 * 1024));
 
   // Create instance.
   auto type_joinable_index = std::unique_ptr<QualifiedIdTypeJoinableIndex>(
       new QualifiedIdTypeJoinableIndex(
           filesystem, std::move(working_path), std::move(metadata_buffer),
-          std::move(document_to_qualified_id_mapper)));
+          std::move(doc_join_info_mapper), std::move(qualified_id_storage)));
   // Initialize existing PersistentStorage. Checksums will be validated.
   ICING_RETURN_IF_ERROR(type_joinable_index->InitializeExistingStorage());
 
@@ -249,25 +303,25 @@ QualifiedIdTypeJoinableIndex::InitializeExistingFiles(
 libtextclassifier3::Status QualifiedIdTypeJoinableIndex::TransferIndex(
     const std::vector<DocumentId>& document_id_old_to_new,
     QualifiedIdTypeJoinableIndex* new_index) const {
-  std::unique_ptr<KeyMapper<DocumentId>::Iterator> iter =
-      document_to_qualified_id_mapper_->GetIterator();
+  std::unique_ptr<KeyMapper<int32_t>::Iterator> iter =
+      doc_join_info_mapper_->GetIterator();
   while (iter->Advance()) {
     DocJoinInfo old_doc_join_info(
         encode_util::DecodeIntFromCString(iter->GetKey()));
-    DocumentId old_ref_document_id = iter->GetValue();
+    int32_t qualified_id_index = iter->GetValue();
+
+    const char* data = qualified_id_storage_->array() + qualified_id_index;
+    std::string_view ref_qualified_id_str(data, strlen(data));
 
-    // Translate to new doc ids.
+    // Translate to new doc id.
     DocumentId new_document_id = GetNewDocumentId(
         document_id_old_to_new, old_doc_join_info.document_id());
-    DocumentId new_ref_document_id =
-        GetNewDocumentId(document_id_old_to_new, old_ref_document_id);
 
-    if (new_document_id != kInvalidDocumentId &&
-        new_ref_document_id != kInvalidDocumentId) {
+    if (new_document_id != kInvalidDocumentId) {
       ICING_RETURN_IF_ERROR(
           new_index->Put(DocJoinInfo(new_document_id,
                                      old_doc_join_info.joinable_property_id()),
-                         new_ref_document_id));
+                         ref_qualified_id_str));
     }
   }
 
@@ -299,7 +353,9 @@ QualifiedIdTypeJoinableIndex::PersistMetadataToDisk() {
 
 libtextclassifier3::Status
 QualifiedIdTypeJoinableIndex::PersistStoragesToDisk() {
-  return document_to_qualified_id_mapper_->PersistToDisk();
+  ICING_RETURN_IF_ERROR(doc_join_info_mapper_->PersistToDisk());
+  ICING_RETURN_IF_ERROR(qualified_id_storage_->PersistToDisk());
+  return libtextclassifier3::Status::OK;
 }
 
 libtextclassifier3::StatusOr<Crc32>
@@ -309,7 +365,12 @@ QualifiedIdTypeJoinableIndex::ComputeInfoChecksum() {
 
 libtextclassifier3::StatusOr<Crc32>
 QualifiedIdTypeJoinableIndex::ComputeStoragesChecksum() {
-  return document_to_qualified_id_mapper_->ComputeChecksum();
+  ICING_ASSIGN_OR_RETURN(Crc32 doc_join_info_mapper_crc,
+                         doc_join_info_mapper_->ComputeChecksum());
+  ICING_ASSIGN_OR_RETURN(Crc32 qualified_id_storage_crc,
+                         qualified_id_storage_->ComputeChecksum());
+
+  return Crc32(doc_join_info_mapper_crc.Get() ^ qualified_id_storage_crc.Get());
 }
 
 }  // namespace lib
diff --git a/icing/join/qualified-id-type-joinable-index.h b/icing/join/qualified-id-type-joinable-index.h
index 794f33f..1127641 100644
--- a/icing/join/qualified-id-type-joinable-index.h
+++ b/icing/join/qualified-id-type-joinable-index.h
@@ -23,6 +23,7 @@
 
 #include "icing/text_classifier/lib3/utils/base/status.h"
 #include "icing/text_classifier/lib3/utils/base/statusor.h"
+#include "icing/file/file-backed-vector.h"
 #include "icing/file/filesystem.h"
 #include "icing/file/persistent-storage.h"
 #include "icing/join/doc-join-info.h"
@@ -59,8 +60,6 @@ class QualifiedIdTypeJoinableIndex : public PersistentStorage {
 
   static constexpr WorkingPathType kWorkingPathType =
       WorkingPathType::kDirectory;
-  static constexpr std::string_view kFilePrefix =
-      "qualified_id_type_joinable_index";
 
   // Creates a QualifiedIdTypeJoinableIndex instance to store qualified ids for
   // future joining search. If any of the underlying file is missing, then
@@ -112,24 +111,26 @@ class QualifiedIdTypeJoinableIndex : public PersistentStorage {
   ~QualifiedIdTypeJoinableIndex() override;
 
   // Puts a new data into index: DocJoinInfo (DocumentId, JoinablePropertyId)
-  // references to ref_document_id.
+  // references to ref_qualified_id_str (the identifier of another document).
+  //
+  // REQUIRES: ref_qualified_id_str contains no '\0'.
   //
   // Returns:
   //   - OK on success
   //   - INVALID_ARGUMENT_ERROR if doc_join_info is invalid
   //   - Any KeyMapper errors
   libtextclassifier3::Status Put(const DocJoinInfo& doc_join_info,
-                                 DocumentId ref_document_id);
+                                 std::string_view ref_qualified_id_str);
 
-  // Gets the referenced DocumentId by DocJoinInfo.
+  // Gets the referenced document's qualified id string by DocJoinInfo.
   //
   // Returns:
-  //   - DocumentId referenced by the given DocJoinInfo (DocumentId,
+  //   - A qualified id string referenced by the given DocJoinInfo (DocumentId,
   //     JoinablePropertyId) on success
   //   - INVALID_ARGUMENT_ERROR if doc_join_info is invalid
   //   - NOT_FOUND_ERROR if doc_join_info doesn't exist
   //   - Any KeyMapper errors
-  libtextclassifier3::StatusOr<DocumentId> Get(
+  libtextclassifier3::StatusOr<std::string_view> Get(
       const DocJoinInfo& doc_join_info) const;
 
   // Reduces internal file sizes by reclaiming space and ids of deleted
@@ -158,7 +159,7 @@ class QualifiedIdTypeJoinableIndex : public PersistentStorage {
   //   - INTERNAL_ERROR on I/O error
   libtextclassifier3::Status Clear();
 
-  int32_t size() const { return document_to_qualified_id_mapper_->num_keys(); }
+  int32_t size() const { return doc_join_info_mapper_->num_keys(); }
 
   bool empty() const { return size() == 0; }
 
@@ -178,11 +179,13 @@ class QualifiedIdTypeJoinableIndex : public PersistentStorage {
   explicit QualifiedIdTypeJoinableIndex(
       const Filesystem& filesystem, std::string&& working_path,
       std::unique_ptr<uint8_t[]> metadata_buffer,
-      std::unique_ptr<KeyMapper<DocumentId>> key_mapper)
+      std::unique_ptr<KeyMapper<int32_t>> doc_join_info_mapper,
+      std::unique_ptr<FileBackedVector<char>> qualified_id_storage)
       : PersistentStorage(filesystem, std::move(working_path),
                           kWorkingPathType),
         metadata_buffer_(std::move(metadata_buffer)),
-        document_to_qualified_id_mapper_(std::move(key_mapper)) {}
+        doc_join_info_mapper_(std::move(doc_join_info_mapper)),
+        qualified_id_storage_(std::move(qualified_id_storage)) {}
 
   static libtextclassifier3::StatusOr<
       std::unique_ptr<QualifiedIdTypeJoinableIndex>>
@@ -255,9 +258,12 @@ class QualifiedIdTypeJoinableIndex : public PersistentStorage {
   std::unique_ptr<uint8_t[]> metadata_buffer_;
 
   // Persistent KeyMapper for mapping (encoded) DocJoinInfo (DocumentId,
-  // JoinablePropertyId) to another referenced DocumentId (converted from
-  // qualified id string).
-  std::unique_ptr<KeyMapper<DocumentId>> document_to_qualified_id_mapper_;
+  // JoinablePropertyId) to another referenced document's qualified id string
+  // index in qualified_id_storage_.
+  std::unique_ptr<KeyMapper<int32_t>> doc_join_info_mapper_;
+
+  // Storage for qualified id strings.
+  std::unique_ptr<FileBackedVector<char>> qualified_id_storage_;
 
   // TODO(b/268521214): add delete propagation storage
 };
diff --git a/icing/join/qualified-id-type-joinable-index_test.cc b/icing/join/qualified-id-type-joinable-index_test.cc
index 6cbc9e4..745b0c1 100644
--- a/icing/join/qualified-id-type-joinable-index_test.cc
+++ b/icing/join/qualified-id-type-joinable-index_test.cc
@@ -16,10 +16,12 @@
 
 #include <memory>
 #include <string>
+#include <string_view>
 
 #include "icing/text_classifier/lib3/utils/base/status.h"
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
+#include "icing/file/file-backed-vector.h"
 #include "icing/file/filesystem.h"
 #include "icing/file/persistent-storage.h"
 #include "icing/join/doc-join-info.h"
@@ -89,8 +91,8 @@ TEST_F(QualifiedIdTypeJoinableIndexTest, InitializeNewFiles) {
 
   // Metadata file should be initialized correctly for both info and crcs
   // sections.
-  const std::string metadata_file_path = absl_ports::StrCat(
-      working_path_, "/", QualifiedIdTypeJoinableIndex::kFilePrefix, ".m");
+  const std::string metadata_file_path =
+      absl_ports::StrCat(working_path_, "/metadata");
   auto metadata_buffer = std::make_unique<uint8_t[]>(
       QualifiedIdTypeJoinableIndex::kMetadataFileSize);
   ASSERT_THAT(
@@ -134,13 +136,13 @@ TEST_F(QualifiedIdTypeJoinableIndexTest,
   // Insert some data.
   ICING_ASSERT_OK(
       index->Put(DocJoinInfo(/*document_id=*/1, /*joinable_property_id=*/20),
-                 /*ref_document_id=*/0));
+                 /*ref_qualified_id_str=*/"namespace#uriA"));
   ICING_ASSERT_OK(
       index->Put(DocJoinInfo(/*document_id=*/3, /*joinable_property_id=*/20),
-                 /*ref_document_id=*/2));
+                 /*ref_qualified_id_str=*/"namespace#uriB"));
   ICING_ASSERT_OK(
       index->Put(DocJoinInfo(/*document_id=*/5, /*joinable_property_id=*/20),
-                 /*ref_document_id=*/4));
+                 /*ref_qualified_id_str=*/"namespace#uriC"));
 
   // Without calling PersistToDisk, checksums will not be recomputed or synced
   // to disk, so initializing another instance on the same files should fail.
@@ -158,13 +160,13 @@ TEST_F(QualifiedIdTypeJoinableIndexTest,
   // Insert some data.
   ICING_ASSERT_OK(
       index1->Put(DocJoinInfo(/*document_id=*/1, /*joinable_property_id=*/20),
-                  /*ref_document_id=*/0));
+                  /*ref_qualified_id_str=*/"namespace#uriA"));
   ICING_ASSERT_OK(
       index1->Put(DocJoinInfo(/*document_id=*/3, /*joinable_property_id=*/20),
-                  /*ref_document_id=*/2));
+                  /*ref_qualified_id_str=*/"namespace#uriB"));
   ICING_ASSERT_OK(
       index1->Put(DocJoinInfo(/*document_id=*/5, /*joinable_property_id=*/20),
-                  /*ref_document_id=*/4));
+                  /*ref_qualified_id_str=*/"namespace#uriC"));
   ASSERT_THAT(index1, Pointee(SizeIs(3)));
 
   // After calling PersistToDisk, all checksums should be recomputed and synced
@@ -178,13 +180,13 @@ TEST_F(QualifiedIdTypeJoinableIndexTest,
   EXPECT_THAT(index2, Pointee(SizeIs(3)));
   EXPECT_THAT(
       index2->Get(DocJoinInfo(/*document_id=*/1, /*joinable_property_id=*/20)),
-      IsOkAndHolds(0));
+      IsOkAndHolds(/*ref_qualified_id_str=*/"namespace#uriA"));
   EXPECT_THAT(
       index2->Get(DocJoinInfo(/*document_id=*/3, /*joinable_property_id=*/20)),
-      IsOkAndHolds(2));
+      IsOkAndHolds(/*ref_qualified_id_str=*/"namespace#uriB"));
   EXPECT_THAT(
       index2->Get(DocJoinInfo(/*document_id=*/5, /*joinable_property_id=*/20)),
-      IsOkAndHolds(4));
+      IsOkAndHolds(/*ref_qualified_id_str=*/"namespace#uriC"));
 }
 
 TEST_F(QualifiedIdTypeJoinableIndexTest,
@@ -198,13 +200,13 @@ TEST_F(QualifiedIdTypeJoinableIndexTest,
     // Insert some data.
     ICING_ASSERT_OK(
         index->Put(DocJoinInfo(/*document_id=*/1, /*joinable_property_id=*/20),
-                   /*ref_document_id=*/0));
+                   /*ref_qualified_id_str=*/"namespace#uriA"));
     ICING_ASSERT_OK(
         index->Put(DocJoinInfo(/*document_id=*/3, /*joinable_property_id=*/20),
-                   /*ref_document_id=*/2));
+                   /*ref_qualified_id_str=*/"namespace#uriB"));
     ICING_ASSERT_OK(
         index->Put(DocJoinInfo(/*document_id=*/5, /*joinable_property_id=*/20),
-                   /*ref_document_id=*/4));
+                   /*ref_qualified_id_str=*/"namespace#uriC"));
     ASSERT_THAT(index, Pointee(SizeIs(3)));
   }
 
@@ -219,13 +221,13 @@ TEST_F(QualifiedIdTypeJoinableIndexTest,
     EXPECT_THAT(index, Pointee(SizeIs(3)));
     EXPECT_THAT(index->Get(DocJoinInfo(/*document_id=*/1,
                                        /*joinable_property_id=*/20)),
-                IsOkAndHolds(0));
+                IsOkAndHolds("namespace#uriA"));
     EXPECT_THAT(index->Get(DocJoinInfo(/*document_id=*/3,
                                        /*joinable_property_id=*/20)),
-                IsOkAndHolds(2));
+                IsOkAndHolds("namespace#uriB"));
     EXPECT_THAT(index->Get(DocJoinInfo(/*document_id=*/5,
                                        /*joinable_property_id=*/20)),
-                IsOkAndHolds(4));
+                IsOkAndHolds("namespace#uriC"));
   }
 }
 
@@ -238,15 +240,15 @@ TEST_F(QualifiedIdTypeJoinableIndexTest,
         QualifiedIdTypeJoinableIndex::Create(filesystem_, working_path_));
     ICING_ASSERT_OK(
         index->Put(DocJoinInfo(/*document_id=*/1, /*joinable_property_id=*/20),
-                   /*ref_document_id=*/0));
+                   /*ref_qualified_id_str=*/"namespace#uriA"));
 
     ICING_ASSERT_OK(index->PersistToDisk());
   }
 
   {
     // Manually change magic and update checksum
-    const std::string metadata_file_path = absl_ports::StrCat(
-        working_path_, "/", QualifiedIdTypeJoinableIndex::kFilePrefix, ".m");
+    const std::string metadata_file_path =
+        absl_ports::StrCat(working_path_, "/metadata");
     ScopedFd metadata_sfd(filesystem_.OpenForWrite(metadata_file_path.c_str()));
     ASSERT_THAT(metadata_sfd.is_valid(), IsTrue());
 
@@ -290,14 +292,14 @@ TEST_F(QualifiedIdTypeJoinableIndexTest,
         QualifiedIdTypeJoinableIndex::Create(filesystem_, working_path_));
     ICING_ASSERT_OK(
         index->Put(DocJoinInfo(/*document_id=*/1, /*joinable_property_id=*/20),
-                   /*ref_document_id=*/0));
+                   /*ref_qualified_id_str=*/"namespace#uriA"));
 
     ICING_ASSERT_OK(index->PersistToDisk());
   }
 
   {
-    const std::string metadata_file_path = absl_ports::StrCat(
-        working_path_, "/", QualifiedIdTypeJoinableIndex::kFilePrefix, ".m");
+    const std::string metadata_file_path =
+        absl_ports::StrCat(working_path_, "/metadata");
     ScopedFd metadata_sfd(filesystem_.OpenForWrite(metadata_file_path.c_str()));
     ASSERT_THAT(metadata_sfd.is_valid(), IsTrue());
 
@@ -337,14 +339,14 @@ TEST_F(QualifiedIdTypeJoinableIndexTest,
         QualifiedIdTypeJoinableIndex::Create(filesystem_, working_path_));
     ICING_ASSERT_OK(
         index->Put(DocJoinInfo(/*document_id=*/1, /*joinable_property_id=*/20),
-                   /*ref_document_id=*/0));
+                   /*ref_qualified_id_str=*/"namespace#uriA"));
 
     ICING_ASSERT_OK(index->PersistToDisk());
   }
 
   {
-    const std::string metadata_file_path = absl_ports::StrCat(
-        working_path_, "/", QualifiedIdTypeJoinableIndex::kFilePrefix, ".m");
+    const std::string metadata_file_path =
+        absl_ports::StrCat(working_path_, "/metadata");
     ScopedFd metadata_sfd(filesystem_.OpenForWrite(metadata_file_path.c_str()));
     ASSERT_THAT(metadata_sfd.is_valid(), IsTrue());
 
@@ -376,9 +378,8 @@ TEST_F(QualifiedIdTypeJoinableIndexTest,
                        HasSubstr("Invalid info crc")));
 }
 
-TEST_F(
-    QualifiedIdTypeJoinableIndexTest,
-    InitializeExistingFilesWithCorruptedDocumentToQualifiedIdMapperShouldFail) {
+TEST_F(QualifiedIdTypeJoinableIndexTest,
+       InitializeExistingFilesWithCorruptedDocJoinInfoMapperShouldFail) {
   {
     // Create new qualified id type joinable index
     ICING_ASSERT_OK_AND_ASSIGN(
@@ -386,19 +387,18 @@ TEST_F(
         QualifiedIdTypeJoinableIndex::Create(filesystem_, working_path_));
     ICING_ASSERT_OK(
         index->Put(DocJoinInfo(/*document_id=*/1, /*joinable_property_id=*/20),
-                   /*ref_document_id=*/0));
+                   /*ref_qualified_id_str=*/"namespace#uriA"));
 
     ICING_ASSERT_OK(index->PersistToDisk());
   }
 
   {
-    // Corrupt document_to_qualified_id_mapper manually.
-    std::string mapper_working_path = absl_ports::StrCat(
-        working_path_, "/", QualifiedIdTypeJoinableIndex::kFilePrefix,
-        "_mapper");
+    // Corrupt doc_join_info_mapper manually.
+    std::string mapper_working_path =
+        absl_ports::StrCat(working_path_, "/doc_join_info_mapper");
     ICING_ASSERT_OK_AND_ASSIGN(
-        std::unique_ptr<PersistentHashMapKeyMapper<DocumentId>> mapper,
-        PersistentHashMapKeyMapper<DocumentId>::Create(
+        std::unique_ptr<PersistentHashMapKeyMapper<int32_t>> mapper,
+        PersistentHashMapKeyMapper<int32_t>::Create(
             filesystem_, std::move(mapper_working_path)));
     ICING_ASSERT_OK_AND_ASSIGN(Crc32 old_crc, mapper->ComputeChecksum());
     ICING_ASSERT_OK(mapper->Put("foo", 12345));
@@ -408,7 +408,47 @@ TEST_F(
   }
 
   // Attempt to create the qualified id type joinable index with corrupted
-  // document_to_qualified_id_mapper. This should fail.
+  // doc_join_info_mapper. This should fail.
+  EXPECT_THAT(QualifiedIdTypeJoinableIndex::Create(filesystem_, working_path_),
+              StatusIs(libtextclassifier3::StatusCode::FAILED_PRECONDITION,
+                       HasSubstr("Invalid storages crc")));
+}
+
+TEST_F(QualifiedIdTypeJoinableIndexTest,
+       InitializeExistingFilesWithCorruptedQualifiedIdStorageShouldFail) {
+  {
+    // Create new qualified id type joinable index
+    ICING_ASSERT_OK_AND_ASSIGN(
+        std::unique_ptr<QualifiedIdTypeJoinableIndex> index,
+        QualifiedIdTypeJoinableIndex::Create(filesystem_, working_path_));
+    ICING_ASSERT_OK(
+        index->Put(DocJoinInfo(/*document_id=*/1, /*joinable_property_id=*/20),
+                   /*ref_qualified_id_str=*/"namespace#uriA"));
+
+    ICING_ASSERT_OK(index->PersistToDisk());
+  }
+
+  {
+    // Corrupt qualified_id_storage manually.
+    std::string qualified_id_storage_path =
+        absl_ports::StrCat(working_path_, "/qualified_id_storage");
+    ICING_ASSERT_OK_AND_ASSIGN(
+        std::unique_ptr<FileBackedVector<char>> qualified_id_storage,
+        FileBackedVector<char>::Create(
+            filesystem_, qualified_id_storage_path,
+            MemoryMappedFile::Strategy::READ_WRITE_AUTO_SYNC));
+    ICING_ASSERT_OK_AND_ASSIGN(Crc32 old_crc,
+                               qualified_id_storage->ComputeChecksum());
+    ICING_ASSERT_OK(qualified_id_storage->Append('a'));
+    ICING_ASSERT_OK(qualified_id_storage->Append('b'));
+    ICING_ASSERT_OK(qualified_id_storage->PersistToDisk());
+    ICING_ASSERT_OK_AND_ASSIGN(Crc32 new_crc,
+                               qualified_id_storage->ComputeChecksum());
+    ASSERT_THAT(old_crc, Not(Eq(new_crc)));
+  }
+
+  // Attempt to create the qualified id type joinable index with corrupted
+  // qualified_id_storage. This should fail.
   EXPECT_THAT(QualifiedIdTypeJoinableIndex::Create(filesystem_, working_path_),
               StatusIs(libtextclassifier3::StatusCode::FAILED_PRECONDITION,
                        HasSubstr("Invalid storages crc")));
@@ -421,8 +461,9 @@ TEST_F(QualifiedIdTypeJoinableIndexTest, InvalidPut) {
       QualifiedIdTypeJoinableIndex::Create(filesystem_, working_path_));
 
   DocJoinInfo default_invalid;
-  EXPECT_THAT(index->Put(default_invalid, /*ref_document_id=*/0),
-              StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
+  EXPECT_THAT(
+      index->Put(default_invalid, /*ref_qualified_id_str=*/"namespace#uriA"),
+      StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
 }
 
 TEST_F(QualifiedIdTypeJoinableIndexTest, InvalidGet) {
@@ -438,13 +479,13 @@ TEST_F(QualifiedIdTypeJoinableIndexTest, InvalidGet) {
 
 TEST_F(QualifiedIdTypeJoinableIndexTest, PutAndGet) {
   DocJoinInfo target_info1(/*document_id=*/1, /*joinable_property_id=*/20);
-  DocumentId ref_document1 = 0;
+  std::string_view ref_qualified_id_str_a = "namespace#uriA";
 
   DocJoinInfo target_info2(/*document_id=*/3, /*joinable_property_id=*/13);
-  DocumentId ref_document2 = 2;
+  std::string_view ref_qualified_id_str_b = "namespace#uriB";
 
   DocJoinInfo target_info3(/*document_id=*/4, /*joinable_property_id=*/4);
-  DocumentId ref_document3 = ref_document1;
+  std::string_view ref_qualified_id_str_c = "namespace#uriC";
 
   {
     // Create new qualified id type joinable index
@@ -452,17 +493,14 @@ TEST_F(QualifiedIdTypeJoinableIndexTest, PutAndGet) {
         std::unique_ptr<QualifiedIdTypeJoinableIndex> index,
         QualifiedIdTypeJoinableIndex::Create(filesystem_, working_path_));
 
-    EXPECT_THAT(index->Put(target_info1, /*ref_document_id=*/ref_document1),
-                IsOk());
-    EXPECT_THAT(index->Put(target_info2, /*ref_document_id=*/ref_document2),
-                IsOk());
-    EXPECT_THAT(index->Put(target_info3, /*ref_document_id=*/ref_document3),
-                IsOk());
+    EXPECT_THAT(index->Put(target_info1, ref_qualified_id_str_a), IsOk());
+    EXPECT_THAT(index->Put(target_info2, ref_qualified_id_str_b), IsOk());
+    EXPECT_THAT(index->Put(target_info3, ref_qualified_id_str_c), IsOk());
     EXPECT_THAT(index, Pointee(SizeIs(3)));
 
-    EXPECT_THAT(index->Get(target_info1), IsOkAndHolds(ref_document1));
-    EXPECT_THAT(index->Get(target_info2), IsOkAndHolds(ref_document2));
-    EXPECT_THAT(index->Get(target_info3), IsOkAndHolds(ref_document3));
+    EXPECT_THAT(index->Get(target_info1), IsOkAndHolds(ref_qualified_id_str_a));
+    EXPECT_THAT(index->Get(target_info2), IsOkAndHolds(ref_qualified_id_str_b));
+    EXPECT_THAT(index->Get(target_info3), IsOkAndHolds(ref_qualified_id_str_c));
 
     ICING_ASSERT_OK(index->PersistToDisk());
   }
@@ -472,15 +510,15 @@ TEST_F(QualifiedIdTypeJoinableIndexTest, PutAndGet) {
       std::unique_ptr<QualifiedIdTypeJoinableIndex> index,
       QualifiedIdTypeJoinableIndex::Create(filesystem_, working_path_));
   EXPECT_THAT(index, Pointee(SizeIs(3)));
-  EXPECT_THAT(index->Get(target_info1), IsOkAndHolds(ref_document1));
-  EXPECT_THAT(index->Get(target_info2), IsOkAndHolds(ref_document2));
-  EXPECT_THAT(index->Get(target_info3), IsOkAndHolds(ref_document3));
+  EXPECT_THAT(index->Get(target_info1), IsOkAndHolds(ref_qualified_id_str_a));
+  EXPECT_THAT(index->Get(target_info2), IsOkAndHolds(ref_qualified_id_str_b));
+  EXPECT_THAT(index->Get(target_info3), IsOkAndHolds(ref_qualified_id_str_c));
 }
 
 TEST_F(QualifiedIdTypeJoinableIndexTest,
        GetShouldReturnNotFoundErrorIfNotExist) {
   DocJoinInfo target_info(/*document_id=*/1, /*joinable_property_id=*/20);
-  DocumentId ref_document = 0;
+  std::string_view ref_qualified_id_str = "namespace#uriA";
 
   // Create new qualified id type joinable index
   ICING_ASSERT_OK_AND_ASSIGN(
@@ -491,8 +529,8 @@ TEST_F(QualifiedIdTypeJoinableIndexTest,
   EXPECT_THAT(index->Get(target_info),
               StatusIs(libtextclassifier3::StatusCode::NOT_FOUND));
 
-  ICING_ASSERT_OK(index->Put(target_info, /*ref_document_id=*/ref_document));
-  ASSERT_THAT(index->Get(target_info), IsOkAndHolds(ref_document));
+  ICING_ASSERT_OK(index->Put(target_info, ref_qualified_id_str));
+  ASSERT_THAT(index->Get(target_info), IsOkAndHolds(ref_qualified_id_str));
 
   // Get another non-existing entry. This should get NOT_FOUND_ERROR.
   DocJoinInfo another_target_info(/*document_id=*/2,
@@ -542,34 +580,30 @@ TEST_F(QualifiedIdTypeJoinableIndexTest, Optimize) {
 
   ICING_ASSERT_OK(
       index->Put(DocJoinInfo(/*document_id=*/3, /*joinable_property_id=*/10),
-                 /*ref_document_id=*/0));
+                 /*ref_qualified_id_str=*/"namespace#uriA"));
   ICING_ASSERT_OK(
       index->Put(DocJoinInfo(/*document_id=*/5, /*joinable_property_id=*/3),
-                 /*ref_document_id=*/0));
+                 /*ref_qualified_id_str=*/"namespace#uriA"));
   ICING_ASSERT_OK(
       index->Put(DocJoinInfo(/*document_id=*/8, /*joinable_property_id=*/9),
-                 /*ref_document_id=*/2));
+                 /*ref_qualified_id_str=*/"namespace#uriB"));
   ICING_ASSERT_OK(
       index->Put(DocJoinInfo(/*document_id=*/13, /*joinable_property_id=*/4),
-                 /*ref_document_id=*/12));
+                 /*ref_qualified_id_str=*/"namespace#uriC"));
   ICING_ASSERT_OK(
       index->Put(DocJoinInfo(/*document_id=*/21, /*joinable_property_id=*/12),
-                 /*ref_document_id=*/12));
+                 /*ref_qualified_id_str=*/"namespace#uriC"));
   index->set_last_added_document_id(21);
 
   ASSERT_THAT(index, Pointee(SizeIs(5)));
 
-  // Used doc id: 0, 2, 3, 5, 8, 12, 13, 21.
-  // Delete doc id = 2, 5, compress and keep the rest.
+  // Delete doc id = 5, 8, compress and keep the rest.
   std::vector<DocumentId> document_id_old_to_new(22, kInvalidDocumentId);
-  document_id_old_to_new[0] = 0;
-  document_id_old_to_new[3] = 1;
-  document_id_old_to_new[8] = 2;
-  document_id_old_to_new[12] = 3;
-  document_id_old_to_new[13] = 4;
-  document_id_old_to_new[21] = 5;
-
-  DocumentId new_last_added_document_id = 5;
+  document_id_old_to_new[3] = 0;
+  document_id_old_to_new[13] = 1;
+  document_id_old_to_new[21] = 2;
+
+  DocumentId new_last_added_document_id = 2;
   EXPECT_THAT(
       index->Optimize(document_id_old_to_new, new_last_added_document_id),
       IsOk());
@@ -577,48 +611,43 @@ TEST_F(QualifiedIdTypeJoinableIndexTest, Optimize) {
   EXPECT_THAT(index->last_added_document_id(), Eq(new_last_added_document_id));
 
   // Verify Put and Get API still work normally after Optimize().
-  // (old_doc_id=3, joinable_property_id=10) had old referenced doc_id = 0,
-  // which is now (doc_id=1, joinable_property_id=10) and referenced doc_id = 0.
+  // (old_doc_id=3, joinable_property_id=10), which is now (doc_id=0,
+  // joinable_property_id=10), has referenced qualified id str =
+  // "namespace#uriA".
   EXPECT_THAT(
-      index->Get(DocJoinInfo(/*document_id=*/1, /*joinable_property_id=*/10)),
-      IsOkAndHolds(0));
-
-  // (old_doc_id=5, joinable_property_id=3) had old referenced doc_id = 0,
-  // which is now not found since we've deleted old_doc_id = 5. It is not
-  // testable via Get() because there is no valid doc_id mapping for old_doc_id
-  // = 5 and we cannot generate a valid DocJoinInfo for it.
-
-  // (old_doc_id=8, joinable_property_id=9) had old referenced doc_id = 2,
-  // which is now (doc_id=2, joinable_property_id=9), but since we've deleted
-  // old referenced doc_id = 2, this data should not be found after
-  // optimization.
-  EXPECT_THAT(
-      index->Get(DocJoinInfo(/*document_id=*/2, /*joinable_property_id=*/9)),
-      StatusIs(libtextclassifier3::StatusCode::NOT_FOUND));
+      index->Get(DocJoinInfo(/*document_id=*/0, /*joinable_property_id=*/10)),
+      IsOkAndHolds("namespace#uriA"));
+
+  // (old_doc_id=5, joinable_property_id=3) and (old_doc_id=8,
+  // joinable_property_id=9) are now not found since we've deleted old_doc_id =
+  // 5, 8. It is not testable via Get() because there is no valid doc_id mapping
+  // for old_doc_id = 5, 8 and we cannot generate a valid DocJoinInfo for it.
 
-  // (old_doc_id=13, joinable_property_id=4) had old referenced doc_id = 12,
-  // which is now (doc_id=4, joinable_property_id=4) and referenced doc_id = 3.
+  // (old_doc_id=13, joinable_property_id=4), which is now (doc_id=1,
+  // joinable_property_id=4), has referenced qualified id str =
+  // "namespace#uriC".
   EXPECT_THAT(
-      index->Get(DocJoinInfo(/*document_id=*/4, /*joinable_property_id=*/4)),
-      IsOkAndHolds(3));
+      index->Get(DocJoinInfo(/*document_id=*/1, /*joinable_property_id=*/4)),
+      IsOkAndHolds("namespace#uriC"));
 
-  // (old_doc_id=21, joinable_property_id=12) had old referenced doc_id = 12,
-  // which is now (doc_id=5, joinable_property_id=12) and referenced doc_id = 3.
+  // (old_doc_id=21, joinable_property_id=12), which is now (doc_id=2,
+  // joinable_property_id=12), has referenced qualified id str =
+  // "namespace#uriC".
   EXPECT_THAT(
-      index->Get(DocJoinInfo(/*document_id=*/5, /*joinable_property_id=*/12)),
-      IsOkAndHolds(3));
+      index->Get(DocJoinInfo(/*document_id=*/2, /*joinable_property_id=*/12)),
+      IsOkAndHolds("namespace#uriC"));
 
   // Joinable index should be able to work normally after Optimize().
   ICING_ASSERT_OK(
       index->Put(DocJoinInfo(/*document_id=*/99, /*joinable_property_id=*/2),
-                 /*ref_document_id=*/90));
+                 /*ref_qualified_id_str=*/"namespace#uriD"));
   index->set_last_added_document_id(99);
 
   EXPECT_THAT(index, Pointee(SizeIs(4)));
   EXPECT_THAT(index->last_added_document_id(), Eq(99));
   EXPECT_THAT(index->Get(DocJoinInfo(/*document_id=*/99,
                                      /*joinable_property_id=*/2)),
-              IsOkAndHolds(90));
+              IsOkAndHolds("namespace#uriD"));
 }
 
 TEST_F(QualifiedIdTypeJoinableIndexTest, OptimizeOutOfRangeDocumentId) {
@@ -628,7 +657,7 @@ TEST_F(QualifiedIdTypeJoinableIndexTest, OptimizeOutOfRangeDocumentId) {
 
   ICING_ASSERT_OK(
       index->Put(DocJoinInfo(/*document_id=*/99, /*joinable_property_id=*/10),
-                 /*ref_document_id=*/91));
+                 /*ref_qualified_id_str=*/"namespace#uriA"));
   index->set_last_added_document_id(99);
 
   // Create document_id_old_to_new with size = 1. Optimize should handle out of
@@ -653,19 +682,19 @@ TEST_F(QualifiedIdTypeJoinableIndexTest, OptimizeDeleteAll) {
 
   ICING_ASSERT_OK(
       index->Put(DocJoinInfo(/*document_id=*/3, /*joinable_property_id=*/10),
-                 /*ref_document_id=*/0));
+                 /*ref_qualified_id_str=*/"namespace#uriA"));
   ICING_ASSERT_OK(
       index->Put(DocJoinInfo(/*document_id=*/5, /*joinable_property_id=*/3),
-                 /*ref_document_id=*/0));
+                 /*ref_qualified_id_str=*/"namespace#uriA"));
   ICING_ASSERT_OK(
       index->Put(DocJoinInfo(/*document_id=*/8, /*joinable_property_id=*/9),
-                 /*ref_document_id=*/2));
+                 /*ref_qualified_id_str=*/"namespace#uriB"));
   ICING_ASSERT_OK(
       index->Put(DocJoinInfo(/*document_id=*/13, /*joinable_property_id=*/4),
-                 /*ref_document_id=*/12));
+                 /*ref_qualified_id_str=*/"namespace#uriC"));
   ICING_ASSERT_OK(
       index->Put(DocJoinInfo(/*document_id=*/21, /*joinable_property_id=*/12),
-                 /*ref_document_id=*/12));
+                 /*ref_qualified_id_str=*/"namespace#uriC"));
   index->set_last_added_document_id(21);
 
   // Delete all documents.
@@ -690,9 +719,12 @@ TEST_F(QualifiedIdTypeJoinableIndexTest, Clear) {
   ICING_ASSERT_OK_AND_ASSIGN(
       std::unique_ptr<QualifiedIdTypeJoinableIndex> index,
       QualifiedIdTypeJoinableIndex::Create(filesystem_, working_path_));
-  ICING_ASSERT_OK(index->Put(target_info1, /*ref_document_id=*/0));
-  ICING_ASSERT_OK(index->Put(target_info2, /*ref_document_id=*/2));
-  ICING_ASSERT_OK(index->Put(target_info3, /*ref_document_id=*/4));
+  ICING_ASSERT_OK(
+      index->Put(target_info1, /*ref_qualified_id_str=*/"namespace#uriA"));
+  ICING_ASSERT_OK(
+      index->Put(target_info2, /*ref_qualified_id_str=*/"namespace#uriB"));
+  ICING_ASSERT_OK(
+      index->Put(target_info3, /*ref_qualified_id_str=*/"namespace#uriC"));
   ASSERT_THAT(index, Pointee(SizeIs(3)));
   index->set_last_added_document_id(6);
   ASSERT_THAT(index->last_added_document_id(), Eq(6));
@@ -711,11 +743,12 @@ TEST_F(QualifiedIdTypeJoinableIndexTest, Clear) {
 
   // Joinable index should be able to work normally after Clear().
   DocJoinInfo target_info4(/*document_id=*/2, /*joinable_property_id=*/19);
-  ICING_ASSERT_OK(index->Put(target_info4, /*ref_document_id=*/0));
+  ICING_ASSERT_OK(
+      index->Put(target_info4, /*ref_qualified_id_str=*/"namespace#uriD"));
   index->set_last_added_document_id(2);
 
   EXPECT_THAT(index->last_added_document_id(), Eq(2));
-  EXPECT_THAT(index->Get(target_info4), IsOkAndHolds(0));
+  EXPECT_THAT(index->Get(target_info4), IsOkAndHolds("namespace#uriD"));
 
   ICING_ASSERT_OK(index->PersistToDisk());
   index.reset();
@@ -730,7 +763,7 @@ TEST_F(QualifiedIdTypeJoinableIndexTest, Clear) {
               StatusIs(libtextclassifier3::StatusCode::NOT_FOUND));
   EXPECT_THAT(index->Get(target_info3),
               StatusIs(libtextclassifier3::StatusCode::NOT_FOUND));
-  EXPECT_THAT(index->Get(target_info4), IsOkAndHolds(0));
+  EXPECT_THAT(index->Get(target_info4), IsOkAndHolds("namespace#uriD"));
 }
 
 }  // namespace
diff --git a/icing/join/qualified-id.cc b/icing/join/qualified-id.cc
index 2a30c44..42e080c 100644
--- a/icing/join/qualified-id.cc
+++ b/icing/join/qualified-id.cc
@@ -40,9 +40,14 @@ bool IsSpecialCharacter(char c) {
 //   A valid index of the separator on success.
 //   std::string::npos if the escape format of content is incorrect.
 //   std::string::npos if the content contains 0 or more than 1 separators.
+//   std::string::npos if the content contains '\0'.
 size_t VerifyFormatAndGetSeparatorPosition(std::string_view content) {
   size_t separator_pos = std::string::npos;
   for (size_t i = 0; i < content.length(); ++i) {
+    if (content[i] == '\0') {
+      return std::string::npos;
+    }
+
     if (content[i] == QualifiedId::kEscapeChar) {
       // Advance to the next character.
       ++i;
diff --git a/icing/join/qualified-id_test.cc b/icing/join/qualified-id_test.cc
index 0c3750a..92bf63e 100644
--- a/icing/join/qualified-id_test.cc
+++ b/icing/join/qualified-id_test.cc
@@ -135,6 +135,24 @@ TEST(QualifiedIdTest, InvalidQualifiedIdWithWrongNumberOfSeparators) {
               StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
 }
 
+TEST(QualifiedIdTest, InvalidQualifiedIdWithStringTerminator) {
+  const char invalid_qualified_id1[] = "names\0pace#uri";
+  EXPECT_THAT(QualifiedId::Parse(std::string_view(invalid_qualified_id1, 14)),
+              StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
+
+  const char invalid_qualified_id2[] = "namespace#ur\0i";
+  EXPECT_THAT(QualifiedId::Parse(std::string_view(invalid_qualified_id2, 14)),
+              StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
+
+  const char invalid_qualified_id3[] = "\0namespace#uri";
+  EXPECT_THAT(QualifiedId::Parse(std::string_view(invalid_qualified_id3, 14)),
+              StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
+
+  const char invalid_qualified_id4[] = "namespace#uri\0";
+  EXPECT_THAT(QualifiedId::Parse(std::string_view(invalid_qualified_id4, 14)),
+              StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
+}
+
 }  // namespace
 
 }  // namespace lib
diff --git a/icing/monkey_test/icing-monkey-test-runner.cc b/icing/monkey_test/icing-monkey-test-runner.cc
index db518bd..89b8e89 100644
--- a/icing/monkey_test/icing-monkey-test-runner.cc
+++ b/icing/monkey_test/icing-monkey-test-runner.cc
@@ -453,9 +453,15 @@ void IcingMonkeyTestRunner::DoOptimize() {
 }
 
 void IcingMonkeyTestRunner::CreateIcingSearchEngine() {
+  std::uniform_int_distribution<> dist(0, 1);
+
   IcingSearchEngineOptions icing_options;
   icing_options.set_index_merge_size(config_.index_merge_size);
   icing_options.set_base_dir(icing_dir_->dir());
+  // The method will be called every time when we ReloadFromDisk(), so randomly
+  // flip this flag to test document store's compatibility.
+  icing_options.set_document_store_namespace_id_fingerprint(
+      (bool)dist(random_));
   icing_ = std::make_unique<IcingSearchEngine>(icing_options);
   ASSERT_THAT(icing_->Initialize().status(), ProtoIsOk());
 }
diff --git a/icing/query/advanced_query_parser/abstract-syntax-tree.h b/icing/query/advanced_query_parser/abstract-syntax-tree.h
index d18f6ea..67049ad 100644
--- a/icing/query/advanced_query_parser/abstract-syntax-tree.h
+++ b/icing/query/advanced_query_parser/abstract-syntax-tree.h
@@ -17,6 +17,7 @@
 
 #include <memory>
 #include <string>
+#include <string_view>
 #include <utility>
 #include <vector>
 
@@ -52,24 +53,29 @@ class Node {
 
 class TerminalNode : public Node {
  public:
-  explicit TerminalNode(std::string value, bool is_prefix)
-      : value_(std::move(value)), is_prefix_(is_prefix) {}
+  explicit TerminalNode(std::string value, std::string_view raw_value,
+                        bool is_prefix)
+      : value_(std::move(value)),
+        raw_value_(raw_value),
+        is_prefix_(is_prefix) {}
 
   const std::string& value() const& { return value_; }
   std::string value() && { return std::move(value_); }
 
   bool is_prefix() const { return is_prefix_; }
 
+  std::string_view raw_value() const { return raw_value_; }
+
  private:
   std::string value_;
+  std::string_view raw_value_;
   bool is_prefix_;
 };
 
 class FunctionNameNode : public TerminalNode {
  public:
   explicit FunctionNameNode(std::string value)
-      : TerminalNode(std::move(value), /*is_prefix=*/false) {}
-
+      : TerminalNode(std::move(value), /*raw_value=*/"", /*is_prefix=*/false) {}
   void Accept(AbstractSyntaxTreeVisitor* visitor) const override {
     visitor->VisitFunctionName(this);
   }
@@ -77,9 +83,9 @@ class FunctionNameNode : public TerminalNode {
 
 class StringNode : public TerminalNode {
  public:
-  explicit StringNode(std::string value, bool is_prefix = false)
-      : TerminalNode(std::move(value), is_prefix) {}
-
+  explicit StringNode(std::string value, std::string_view raw_value,
+                      bool is_prefix = false)
+      : TerminalNode(std::move(value), raw_value, is_prefix) {}
   void Accept(AbstractSyntaxTreeVisitor* visitor) const override {
     visitor->VisitString(this);
   }
@@ -87,9 +93,9 @@ class StringNode : public TerminalNode {
 
 class TextNode : public TerminalNode {
  public:
-  explicit TextNode(std::string value, bool is_prefix = false)
-      : TerminalNode(std::move(value), is_prefix) {}
-
+  explicit TextNode(std::string value, std::string_view raw_value,
+                    bool is_prefix = false)
+      : TerminalNode(std::move(value), raw_value, is_prefix) {}
   void Accept(AbstractSyntaxTreeVisitor* visitor) const override {
     visitor->VisitText(this);
   }
diff --git a/icing/query/advanced_query_parser/abstract-syntax-tree_test.cc b/icing/query/advanced_query_parser/abstract-syntax-tree_test.cc
index a8599fd..5e28278 100644
--- a/icing/query/advanced_query_parser/abstract-syntax-tree_test.cc
+++ b/icing/query/advanced_query_parser/abstract-syntax-tree_test.cc
@@ -27,8 +27,8 @@ namespace {
 using ::testing::ElementsAre;
 
 TEST(AbstractSyntaxTreeTest, Simple) {
-  // foo
-  std::unique_ptr<Node> root = std::make_unique<TextNode>("foo");
+  std::string_view query = "foo";
+  std::unique_ptr<Node> root = std::make_unique<TextNode>("foo", query);
   SimpleVisitor visitor;
   root->Accept(&visitor);
 
@@ -37,16 +37,16 @@ TEST(AbstractSyntaxTreeTest, Simple) {
 }
 
 TEST(AbstractSyntaxTreeTest, Composite) {
-  // (foo bar) OR baz
+  std::string_view query = "(foo bar) OR baz";
   std::vector<std::unique_ptr<Node>> and_args;
-  and_args.push_back(std::make_unique<TextNode>("foo"));
-  and_args.push_back(std::make_unique<TextNode>("bar"));
+  and_args.push_back(std::make_unique<TextNode>("foo", query.substr(1, 3)));
+  and_args.push_back(std::make_unique<TextNode>("bar", query.substr(5, 3)));
   auto and_node =
       std::make_unique<NaryOperatorNode>("AND", std::move(and_args));
 
   std::vector<std::unique_ptr<Node>> or_args;
   or_args.push_back(std::move(and_node));
-  or_args.push_back(std::make_unique<TextNode>("baz"));
+  or_args.push_back(std::make_unique<TextNode>("baz", query.substr(13, 3)));
   std::unique_ptr<Node> root =
       std::make_unique<NaryOperatorNode>("OR", std::move(or_args));
 
@@ -72,9 +72,9 @@ TEST(AbstractSyntaxTreeTest, Function) {
               ElementsAre(EqualsNodeInfo("foo", NodeType::kFunctionName),
                           EqualsNodeInfo("", NodeType::kFunction)));
 
-  // foo("bar")
+  std::string_view query = "foo(\"bar\")";
   std::vector<std::unique_ptr<Node>> args;
-  args.push_back(std::make_unique<StringNode>("bar"));
+  args.push_back(std::make_unique<StringNode>("bar", query.substr(5, 3)));
   root = std::make_unique<FunctionNode>(
       std::make_unique<FunctionNameNode>("foo"), std::move(args));
   visitor = SimpleVisitor();
@@ -85,9 +85,9 @@ TEST(AbstractSyntaxTreeTest, Function) {
                           EqualsNodeInfo("bar", NodeType::kString),
                           EqualsNodeInfo("", NodeType::kFunction)));
 
-  // foo(bar("baz"))
+  query = "foo(bar(\"baz\"))";
   std::vector<std::unique_ptr<Node>> inner_args;
-  inner_args.push_back(std::make_unique<StringNode>("baz"));
+  inner_args.push_back(std::make_unique<StringNode>("baz", query.substr(9, 3)));
   args.clear();
   args.push_back(std::make_unique<FunctionNode>(
       std::make_unique<FunctionNameNode>("bar"), std::move(inner_args)));
@@ -105,14 +105,16 @@ TEST(AbstractSyntaxTreeTest, Function) {
 }
 
 TEST(AbstractSyntaxTreeTest, Restriction) {
-  // sender.name:(IMPORTANT OR URGENT)
+  std::string_view query = "sender.name:(IMPORTANT OR URGENT)";
   std::vector<std::unique_ptr<TextNode>> member_args;
-  member_args.push_back(std::make_unique<TextNode>("sender"));
-  member_args.push_back(std::make_unique<TextNode>("name"));
+  member_args.push_back(
+      std::make_unique<TextNode>("sender", query.substr(0, 6)));
+  member_args.push_back(std::make_unique<TextNode>("name", query.substr(7, 4)));
 
   std::vector<std::unique_ptr<Node>> or_args;
-  or_args.push_back(std::make_unique<TextNode>("IMPORTANT"));
-  or_args.push_back(std::make_unique<TextNode>("URGENT"));
+  or_args.push_back(
+      std::make_unique<TextNode>("IMPORTANT", query.substr(13, 9)));
+  or_args.push_back(std::make_unique<TextNode>("URGENT", query.substr(26, 6)));
 
   std::vector<std::unique_ptr<Node>> has_args;
   has_args.push_back(std::make_unique<MemberNode>(std::move(member_args),
diff --git a/icing/query/advanced_query_parser/function_test.cc b/icing/query/advanced_query_parser/function_test.cc
index 3b3ca40..afd4e04 100644
--- a/icing/query/advanced_query_parser/function_test.cc
+++ b/icing/query/advanced_query_parser/function_test.cc
@@ -63,10 +63,10 @@ TEST(FunctionTest, ParamNotWrongTypeFails) {
       Function function,
       Function::Create(/*return_type=*/DataType::kString, "foo",
                        /*params=*/{Param(DataType::kString)}, TrivialEval()));
-  // foo(bar)
+  std::string_view query = "foo(bar)";
   std::vector<PendingValue> args;
   args.push_back(PendingValue::CreateTextPendingValue(
-      QueryTerm{"bar", /*is_prefix_val=*/false}));
+      QueryTerm{"bar", query.substr(4, 3), /*is_prefix_val=*/false}));
   EXPECT_THAT(function.Eval(std::move(args)),
               StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
 }
@@ -77,10 +77,10 @@ TEST(FunctionTest, ParamRequiredArgSucceeds) {
       Function::Create(/*return_type=*/DataType::kString, "foo",
                        /*params=*/{Param(DataType::kString)}, TrivialEval()));
 
-  // foo("bar")
+  std::string_view query = R"(foo("bar"))";
   std::vector<PendingValue> args;
   args.push_back(PendingValue::CreateStringPendingValue(
-      QueryTerm{"bar", /*is_prefix_val=*/false}));
+      QueryTerm{"bar", query.substr(5, 3), /*is_prefix_val=*/false}));
   ICING_ASSERT_OK_AND_ASSIGN(PendingValue val, function.Eval(std::move(args)));
   EXPECT_THAT(val.is_placeholder(), IsTrue());
 }
@@ -136,19 +136,19 @@ TEST(FunctionTest, MultipleArgsTrailingOptionalSucceeds) {
                               Param(DataType::kString, Cardinality::kOptional)},
                              TrivialEval()));
 
-  // foo("bar")
+  std::string_view query = R"(foo("bar"))";
   std::vector<PendingValue> args;
   args.push_back(PendingValue::CreateStringPendingValue(
-      QueryTerm{"bar", /*is_prefix_val=*/false}));
+      QueryTerm{"bar", query.substr(5, 3), /*is_prefix_val=*/false}));
   ICING_ASSERT_OK_AND_ASSIGN(PendingValue val, function.Eval(std::move(args)));
   EXPECT_THAT(val.is_placeholder(), IsTrue());
 
-  // foo("bar", "baz")
+  query = R"(foo("bar", "baz"))";
   args = std::vector<PendingValue>();
   args.push_back(PendingValue::CreateStringPendingValue(
-      QueryTerm{"bar", /*is_prefix_val=*/false}));
+      QueryTerm{"bar", query.substr(5, 3), /*is_prefix_val=*/false}));
   args.push_back(PendingValue::CreateStringPendingValue(
-      QueryTerm{"baz", /*is_prefix_val=*/false}));
+      QueryTerm{"baz", query.substr(12, 3), /*is_prefix_val=*/false}));
   ICING_ASSERT_OK_AND_ASSIGN(val, function.Eval(std::move(args)));
   EXPECT_THAT(val.is_placeholder(), IsTrue());
 }
@@ -162,30 +162,30 @@ TEST(FunctionTest, MultipleArgsTrailingVariableSucceeds) {
                               Param(DataType::kString, Cardinality::kVariable)},
                              TrivialEval()));
 
-  // foo("bar")
+  std::string_view query = R"(foo("bar"))";
   std::vector<PendingValue> args;
   args.push_back(PendingValue::CreateStringPendingValue(
-      QueryTerm{"bar", /*is_prefix_val=*/false}));
+      QueryTerm{"bar", query.substr(5, 3), /*is_prefix_val=*/false}));
   ICING_ASSERT_OK_AND_ASSIGN(PendingValue val, function.Eval(std::move(args)));
   EXPECT_THAT(val.is_placeholder(), IsTrue());
 
-  // foo("bar", "baz")
+  query = R"(foo("bar", "baz"))";
   args = std::vector<PendingValue>();
   args.push_back(PendingValue::CreateStringPendingValue(
-      QueryTerm{"bar", /*is_prefix_val=*/false}));
+      QueryTerm{"bar", query.substr(5, 3), /*is_prefix_val=*/false}));
   args.push_back(PendingValue::CreateStringPendingValue(
-      QueryTerm{"baz", /*is_prefix_val=*/false}));
+      QueryTerm{"baz", query.substr(12, 3), /*is_prefix_val=*/false}));
   ICING_ASSERT_OK_AND_ASSIGN(val, function.Eval(std::move(args)));
   EXPECT_THAT(val.is_placeholder(), IsTrue());
 
-  // foo("bar", "baz", "bat")
+  query = R"(foo("bar", "baz", "bat"))";
   args = std::vector<PendingValue>();
   args.push_back(PendingValue::CreateStringPendingValue(
-      QueryTerm{"bar", /*is_prefix_val=*/false}));
+      QueryTerm{"bar", query.substr(5, 3), /*is_prefix_val=*/false}));
   args.push_back(PendingValue::CreateStringPendingValue(
-      QueryTerm{"baz", /*is_prefix_val=*/false}));
+      QueryTerm{"baz", query.substr(12, 3), /*is_prefix_val=*/false}));
   args.push_back(PendingValue::CreateStringPendingValue(
-      QueryTerm{"bat", /*is_prefix_val=*/false}));
+      QueryTerm{"bat", query.substr(19, 3), /*is_prefix_val=*/false}));
   ICING_ASSERT_OK_AND_ASSIGN(val, function.Eval(std::move(args)));
   EXPECT_THAT(val.is_placeholder(), IsTrue());
 }
@@ -214,26 +214,26 @@ TEST(FunctionTest, MultipleArgsOptionalBeforeOptionalSucceeds) {
   ICING_ASSERT_OK_AND_ASSIGN(PendingValue val, function.Eval(std::move(args)));
   EXPECT_THAT(val.is_placeholder(), IsTrue());
 
-  // foo("bar")
+  std::string_view query = R"(foo("bar"))";
   args = std::vector<PendingValue>();
   args.push_back(PendingValue::CreateStringPendingValue(
-      QueryTerm{"bar", /*is_prefix_val=*/false}));
+      QueryTerm{"bar", query.substr(5, 3), /*is_prefix_val=*/false}));
   ICING_ASSERT_OK_AND_ASSIGN(val, function.Eval(std::move(args)));
   EXPECT_THAT(val.is_placeholder(), IsTrue());
 
-  // foo("bar", baz)
+  query = R"(foo("bar", baz))";
   args = std::vector<PendingValue>();
   args.push_back(PendingValue::CreateStringPendingValue(
-      QueryTerm{"bar", /*is_prefix_val=*/false}));
+      QueryTerm{"bar", query.substr(5, 3), /*is_prefix_val=*/false}));
   args.push_back(PendingValue::CreateTextPendingValue(
-      QueryTerm{"baz", /*is_prefix_val=*/false}));
+      QueryTerm{"baz", query.substr(11, 3), /*is_prefix_val=*/false}));
   ICING_ASSERT_OK_AND_ASSIGN(val, function.Eval(std::move(args)));
   EXPECT_THAT(val.is_placeholder(), IsTrue());
 
-  // foo(baz)
+  query = R"(foo(baz))";
   args = std::vector<PendingValue>();
   args.push_back(PendingValue::CreateTextPendingValue(
-      QueryTerm{"baz", /*is_prefix_val=*/false}));
+      QueryTerm{"baz", query.substr(4, 3), /*is_prefix_val=*/false}));
   EXPECT_THAT(function.Eval(std::move(args)),
               StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
 }
@@ -252,46 +252,46 @@ TEST(FunctionTest, MultipleArgsOptionalBeforeVariableSucceeds) {
   ICING_ASSERT_OK_AND_ASSIGN(PendingValue val, function.Eval(std::move(args)));
   EXPECT_THAT(val.is_placeholder(), IsTrue());
 
-  // foo("bar")
+  std::string_view query = R"(foo("bar"))";
   args = std::vector<PendingValue>();
   args.push_back(PendingValue::CreateStringPendingValue(
-      QueryTerm{"bar", /*is_prefix_val=*/false}));
+      QueryTerm{"bar", query.substr(5, 3), /*is_prefix_val=*/false}));
   ICING_ASSERT_OK_AND_ASSIGN(val, function.Eval(std::move(args)));
   EXPECT_THAT(val.is_placeholder(), IsTrue());
 
-  // foo("bar", baz)
+  query = R"(foo("bar", baz))";
   args = std::vector<PendingValue>();
   args.push_back(PendingValue::CreateStringPendingValue(
-      QueryTerm{"bar", /*is_prefix_val=*/false}));
+      QueryTerm{"bar", query.substr(5, 3), /*is_prefix_val=*/false}));
   args.push_back(PendingValue::CreateTextPendingValue(
-      QueryTerm{"baz", /*is_prefix_val=*/false}));
+      QueryTerm{"baz", query.substr(11, 3), /*is_prefix_val=*/false}));
   ICING_ASSERT_OK_AND_ASSIGN(val, function.Eval(std::move(args)));
   EXPECT_THAT(val.is_placeholder(), IsTrue());
 
-  // foo("bar", baz, bat)
+  query = R"(foo("bar", baz, bat))";
   args = std::vector<PendingValue>();
   args.push_back(PendingValue::CreateStringPendingValue(
-      QueryTerm{"bar", /*is_prefix_val=*/false}));
+      QueryTerm{"bar", query.substr(5, 3), /*is_prefix_val=*/false}));
   args.push_back(PendingValue::CreateTextPendingValue(
-      QueryTerm{"baz", /*is_prefix_val=*/false}));
+      QueryTerm{"baz", query.substr(11, 3), /*is_prefix_val=*/false}));
   args.push_back(PendingValue::CreateTextPendingValue(
-      QueryTerm{"bat", /*is_prefix_val=*/false}));
+      QueryTerm{"bat", query.substr(16, 3), /*is_prefix_val=*/false}));
   ICING_ASSERT_OK_AND_ASSIGN(val, function.Eval(std::move(args)));
   EXPECT_THAT(val.is_placeholder(), IsTrue());
 
-  // foo(baz)
+  query = R"(foo(baz))";
   args = std::vector<PendingValue>();
   args.push_back(PendingValue::CreateTextPendingValue(
-      QueryTerm{"baz", /*is_prefix_val=*/false}));
+      QueryTerm{"baz", query.substr(4, 3), /*is_prefix_val=*/false}));
   EXPECT_THAT(function.Eval(std::move(args)),
               StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
 
-  // foo(baz, bat)
+  query = R"(foo(baz, bat))";
   args = std::vector<PendingValue>();
   args.push_back(PendingValue::CreateTextPendingValue(
-      QueryTerm{"baz", /*is_prefix_val=*/false}));
+      QueryTerm{"baz", query.substr(4, 3), /*is_prefix_val=*/false}));
   args.push_back(PendingValue::CreateTextPendingValue(
-      QueryTerm{"bat", /*is_prefix_val=*/false}));
+      QueryTerm{"bat", query.substr(9, 3), /*is_prefix_val=*/false}));
   EXPECT_THAT(function.Eval(std::move(args)),
               StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
 }
diff --git a/icing/query/advanced_query_parser/lexer.cc b/icing/query/advanced_query_parser/lexer.cc
index 6cddd96..0dd0bb0 100644
--- a/icing/query/advanced_query_parser/lexer.cc
+++ b/icing/query/advanced_query_parser/lexer.cc
@@ -38,12 +38,13 @@ bool Lexer::ConsumeWhitespace() {
 }
 
 bool Lexer::ConsumeQuerySingleChar() {
+  std::string_view original_text = query_.substr(current_index_, 1);
   switch (current_char_) {
     case ':':
-      tokens_.push_back({":", TokenType::COMPARATOR});
+      tokens_.push_back({":", original_text, TokenType::COMPARATOR});
       break;
     case '*':
-      tokens_.push_back({"", TokenType::STAR});
+      tokens_.push_back({"", original_text, TokenType::STAR});
       break;
     case '-':
       if (in_text_) {
@@ -51,7 +52,7 @@ bool Lexer::ConsumeQuerySingleChar() {
         // in the middle of a TEXT segment (ex. `foo-bar`).
         return false;
       }
-      tokens_.push_back({"", TokenType::MINUS});
+      tokens_.push_back({"", original_text, TokenType::MINUS});
       break;
     default:
       return false;
@@ -61,18 +62,19 @@ bool Lexer::ConsumeQuerySingleChar() {
 }
 
 bool Lexer::ConsumeScoringSingleChar() {
+  std::string_view original_text = query_.substr(current_index_, 1);
   switch (current_char_) {
     case '+':
-      tokens_.push_back({"", TokenType::PLUS});
+      tokens_.push_back({"", original_text, TokenType::PLUS});
       break;
     case '*':
-      tokens_.push_back({"", TokenType::TIMES});
+      tokens_.push_back({"", original_text, TokenType::TIMES});
       break;
     case '/':
-      tokens_.push_back({"", TokenType::DIV});
+      tokens_.push_back({"", original_text, TokenType::DIV});
       break;
     case '-':
-      tokens_.push_back({"", TokenType::MINUS});
+      tokens_.push_back({"", original_text, TokenType::MINUS});
       break;
     default:
       return false;
@@ -82,18 +84,19 @@ bool Lexer::ConsumeScoringSingleChar() {
 }
 
 bool Lexer::ConsumeGeneralSingleChar() {
+  std::string_view original_text = query_.substr(current_index_, 1);
   switch (current_char_) {
     case ',':
-      tokens_.push_back({"", TokenType::COMMA});
+      tokens_.push_back({"", original_text, TokenType::COMMA});
       break;
     case '.':
-      tokens_.push_back({"", TokenType::DOT});
+      tokens_.push_back({"", original_text, TokenType::DOT});
       break;
     case '(':
-      tokens_.push_back({"", TokenType::LPAREN});
+      tokens_.push_back({"", original_text, TokenType::LPAREN});
       break;
     case ')':
-      tokens_.push_back({"", TokenType::RPAREN});
+      tokens_.push_back({"", original_text, TokenType::RPAREN});
       break;
     default:
       return false;
@@ -124,13 +127,17 @@ bool Lexer::ConsumeComparator() {
   // Matching for '<=', '>=', '!=', or '=='.
   char next_char = PeekNext(1);
   if (next_char == '=') {
-    tokens_.push_back({{current_char_, next_char}, TokenType::COMPARATOR});
+    tokens_.push_back({{current_char_, next_char},
+                       query_.substr(current_index_, 2),
+                       TokenType::COMPARATOR});
     Advance(2);
     return true;
   }
   // Now, next_char must not be '='. Let's match for '<' and '>'.
   if (current_char_ == '<' || current_char_ == '>') {
-    tokens_.push_back({{current_char_}, TokenType::COMPARATOR});
+    tokens_.push_back({{current_char_},
+                       query_.substr(current_index_, 1),
+                       TokenType::COMPARATOR});
     Advance();
     return true;
   }
@@ -145,10 +152,11 @@ bool Lexer::ConsumeAndOr() {
   if (current_char_ != next_char) {
     return false;
   }
+  std::string_view original_text = query_.substr(current_index_, 2);
   if (current_char_ == '&') {
-    tokens_.push_back({"", TokenType::AND});
+    tokens_.push_back({"", original_text, TokenType::AND});
   } else {
-    tokens_.push_back({"", TokenType::OR});
+    tokens_.push_back({"", original_text, TokenType::OR});
   }
   Advance(2);
   return true;
@@ -158,37 +166,42 @@ bool Lexer::ConsumeStringLiteral() {
   if (current_char_ != '"') {
     return false;
   }
-  std::string text;
   Advance();
+  int32_t unnormalized_start_pos = current_index_;
   while (current_char_ != '\0' && current_char_ != '"') {
     // When getting a backslash, we will always match the next character, even
     // if the next character is a quotation mark
     if (current_char_ == '\\') {
-      text.push_back(current_char_);
       Advance();
       if (current_char_ == '\0') {
         // In this case, we are missing a terminating quotation mark.
         break;
       }
     }
-    text.push_back(current_char_);
     Advance();
   }
   if (current_char_ == '\0') {
     SyntaxError("missing terminating \" character");
     return false;
   }
-  tokens_.push_back({text, TokenType::STRING});
+  int32_t unnormalized_length = current_index_ - unnormalized_start_pos;
+  std::string_view raw_token_text =
+      query_.substr(unnormalized_start_pos, unnormalized_length);
+  std::string token_text(raw_token_text);
+  tokens_.push_back({std::move(token_text), raw_token_text, TokenType::STRING});
   Advance();
   return true;
 }
 
-bool Lexer::Text() {
+bool Lexer::ConsumeText() {
   if (current_char_ == '\0') {
     return false;
   }
-  tokens_.push_back({"", TokenType::TEXT});
+  tokens_.push_back({"", query_.substr(current_index_, 0), TokenType::TEXT});
   int token_index = tokens_.size() - 1;
+
+  int32_t unnormalized_start_pos = current_index_;
+  int32_t unnormalized_end_pos = current_index_;
   while (!ConsumeNonText() && current_char_ != '\0') {
     in_text_ = true;
     // When getting a backslash in TEXT, unescape it by accepting its following
@@ -203,14 +216,18 @@ bool Lexer::Text() {
     }
     tokens_[token_index].text.push_back(current_char_);
     Advance();
-    if (current_char_ == '(') {
-      // A TEXT followed by a LPAREN is a FUNCTION_NAME.
-      tokens_.back().type = TokenType::FUNCTION_NAME;
-      // No need to break, since NonText() must be true at this point.
-    }
+    unnormalized_end_pos = current_index_;
   }
   in_text_ = false;
 
+  tokens_[token_index].original_text = query_.substr(
+      unnormalized_start_pos, unnormalized_end_pos - unnormalized_start_pos);
+  if (unnormalized_end_pos < query_.length() &&
+      query_[unnormalized_end_pos] == '(') {
+    // A TEXT followed by a LPAREN is a FUNCTION_NAME.
+    tokens_[token_index].type = TokenType::FUNCTION_NAME;
+  }
+
   if (language_ == Lexer::Language::QUERY) {
     std::string &text = tokens_[token_index].text;
     TokenType &type = tokens_[token_index].type;
@@ -234,7 +251,7 @@ Lexer::ExtractTokens() {
     // Clear out any non-text before matching a Text.
     while (ConsumeNonText()) {
     }
-    Text();
+    ConsumeText();
   }
   if (!error_.empty()) {
     return absl_ports::InvalidArgumentError(
diff --git a/icing/query/advanced_query_parser/lexer.h b/icing/query/advanced_query_parser/lexer.h
index f7f06dc..b313fa7 100644
--- a/icing/query/advanced_query_parser/lexer.h
+++ b/icing/query/advanced_query_parser/lexer.h
@@ -48,7 +48,9 @@ class Lexer {
     AND,         // 'AND' | '&&'   Not allowed in SCORING language.
     OR,          // 'OR' | '||'    Not allowed in SCORING language.
     NOT,         // 'NOT'          Not allowed in SCORING language.
-    STRING,      // String literal surrounded by quotation marks
+    STRING,      // String literal surrounded by quotation marks. The
+                 // original_text of a STRING token will not include quotation
+                 // marks.
     TEXT,        // A sequence of chars that are not any above-listed operator
     FUNCTION_NAME,  // A TEXT followed by LPAREN.
     // Whitespaces not inside a string literal will be skipped.
@@ -69,6 +71,10 @@ class Lexer {
     // For other types, this field will be empty.
     std::string text;
 
+    // Lifecycle is dependent on the lifecycle of the string pointed to by
+    // query_.
+    std::string_view original_text;
+
     // The type of the token.
     TokenType type;
   };
@@ -141,8 +147,9 @@ class Lexer {
   }
 
   // Try to match TEXT, FUNCTION_NAME, 'AND', 'OR' and 'NOT'.
-  // Should make sure that NonText() is false before calling into this method.
-  bool Text();
+  // REQUIRES: ConsumeNonText() must be called immediately before calling this
+  // function.
+  bool ConsumeText();
 
   std::string_view query_;
   std::string error_;
diff --git a/icing/query/advanced_query_parser/parser.cc b/icing/query/advanced_query_parser/parser.cc
index 0e4c78d..fd74561 100644
--- a/icing/query/advanced_query_parser/parser.cc
+++ b/icing/query/advanced_query_parser/parser.cc
@@ -55,7 +55,8 @@ libtextclassifier3::StatusOr<std::unique_ptr<TextNode>> Parser::ConsumeText() {
   if (!Match(Lexer::TokenType::TEXT)) {
     return absl_ports::InvalidArgumentError("Unable to consume token as TEXT.");
   }
-  auto text_node = std::make_unique<TextNode>(std::move(current_token_->text));
+  auto text_node = std::make_unique<TextNode>(std::move(current_token_->text),
+                                              current_token_->original_text);
   ++current_token_;
   return text_node;
 }
@@ -81,6 +82,7 @@ Parser::ConsumeStringElement() {
         "Unable to consume token as STRING.");
   }
   std::string text = std::move(current_token_->text);
+  std::string_view raw_text = current_token_->original_text;
   ++current_token_;
 
   bool is_prefix = false;
@@ -89,7 +91,7 @@ Parser::ConsumeStringElement() {
     ++current_token_;
   }
 
-  return std::make_unique<StringNode>(std::move(text), is_prefix);
+  return std::make_unique<StringNode>(std::move(text), raw_text, is_prefix);
 }
 
 libtextclassifier3::StatusOr<std::string> Parser::ConsumeComparator() {
@@ -115,7 +117,9 @@ Parser::ConsumeMember() {
   // at this point. So check for 'STAR' to differentiate the two cases.
   if (Match(Lexer::TokenType::STAR)) {
     Consume(Lexer::TokenType::STAR);
-    text_node = std::make_unique<TextNode>(std::move(*text_node).value(),
+    std::string_view raw_text = text_node->raw_value();
+    std::string text = std::move(*text_node).value();
+    text_node = std::make_unique<TextNode>(std::move(text), raw_text,
                                            /*is_prefix=*/true);
     children.push_back(std::move(text_node));
   } else {
diff --git a/icing/query/advanced_query_parser/parser_test.cc b/icing/query/advanced_query_parser/parser_test.cc
index 502dbd3..824c2ce 100644
--- a/icing/query/advanced_query_parser/parser_test.cc
+++ b/icing/query/advanced_query_parser/parser_test.cc
@@ -46,9 +46,9 @@ TEST(ParserTest, EmptyScoring) {
 }
 
 TEST(ParserTest, SingleTerm) {
-  // Query: "foo"
+  std::string_view query = "foo";
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"foo", Lexer::TokenType::TEXT}};
+      {"foo", query, Lexer::TokenType::TEXT}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<Node> tree_root,
                              parser.ConsumeQuery());
@@ -67,9 +67,10 @@ TEST(ParserTest, SingleTerm) {
 }
 
 TEST(ParserTest, ImplicitAnd) {
-  // Query: "foo bar"
+  std::string_view query = "foo bar";
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"foo", Lexer::TokenType::TEXT}, {"bar", Lexer::TokenType::TEXT}};
+      {"foo", query.substr(0, 3), Lexer::TokenType::TEXT},
+      {"bar", query.substr(4, 3), Lexer::TokenType::TEXT}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<Node> tree_root,
                              parser.ConsumeQuery());
@@ -93,11 +94,11 @@ TEST(ParserTest, ImplicitAnd) {
 }
 
 TEST(ParserTest, Or) {
-  // Query: "foo OR bar"
+  std::string_view query = "foo OR bar";
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"foo", Lexer::TokenType::TEXT},
-      {"", Lexer::TokenType::OR},
-      {"bar", Lexer::TokenType::TEXT}};
+      {"foo", query.substr(0, 3), Lexer::TokenType::TEXT},
+      {"", query.substr(4, 2), Lexer::TokenType::OR},
+      {"bar", query.substr(7, 3), Lexer::TokenType::TEXT}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<Node> tree_root,
                              parser.ConsumeQuery());
@@ -121,11 +122,11 @@ TEST(ParserTest, Or) {
 }
 
 TEST(ParserTest, And) {
-  // Query: "foo AND bar"
+  std::string_view query = "foo AND bar";
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"foo", Lexer::TokenType::TEXT},
-      {"", Lexer::TokenType::AND},
-      {"bar", Lexer::TokenType::TEXT}};
+      {"foo", query.substr(0, 3), Lexer::TokenType::TEXT},
+      {"", query.substr(4, 3), Lexer::TokenType::AND},
+      {"bar", query.substr(8, 4), Lexer::TokenType::TEXT}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<Node> tree_root,
                              parser.ConsumeQuery());
@@ -149,9 +150,10 @@ TEST(ParserTest, And) {
 }
 
 TEST(ParserTest, Not) {
-  // Query: "NOT foo"
+  std::string_view query = "NOT foo";
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"", Lexer::TokenType::NOT}, {"foo", Lexer::TokenType::TEXT}};
+      {"", query.substr(0, 3), Lexer::TokenType::NOT},
+      {"foo", query.substr(4, 3), Lexer::TokenType::TEXT}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<Node> tree_root,
                              parser.ConsumeQuery());
@@ -173,9 +175,10 @@ TEST(ParserTest, Not) {
 }
 
 TEST(ParserTest, Minus) {
-  // Query: "-foo"
+  std::string_view query = "-foo";
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"", Lexer::TokenType::MINUS}, {"foo", Lexer::TokenType::TEXT}};
+      {"", query.substr(0, 1), Lexer::TokenType::MINUS},
+      {"foo", query.substr(1, 3), Lexer::TokenType::TEXT}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<Node> tree_root,
                              parser.ConsumeQuery());
@@ -197,11 +200,11 @@ TEST(ParserTest, Minus) {
 }
 
 TEST(ParserTest, Has) {
-  // Query: "subject:foo"
+  std::string_view query = "subject:foo";
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"subject", Lexer::TokenType::TEXT},
-      {":", Lexer::TokenType::COMPARATOR},
-      {"foo", Lexer::TokenType::TEXT}};
+      {"subject", query.substr(0, 7), Lexer::TokenType::TEXT},
+      {":", query.substr(7, 1), Lexer::TokenType::COMPARATOR},
+      {"foo", query.substr(8, 3), Lexer::TokenType::TEXT}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<Node> tree_root,
                              parser.ConsumeQuery());
@@ -225,13 +228,13 @@ TEST(ParserTest, Has) {
 }
 
 TEST(ParserTest, HasNested) {
-  // Query: "sender.name:foo"
+  std::string_view query = "sender.name:foo";
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"sender", Lexer::TokenType::TEXT},
-      {"", Lexer::TokenType::DOT},
-      {"name", Lexer::TokenType::TEXT},
-      {":", Lexer::TokenType::COMPARATOR},
-      {"foo", Lexer::TokenType::TEXT}};
+      {"sender", query.substr(0, 6), Lexer::TokenType::TEXT},
+      {"", query.substr(6, 1), Lexer::TokenType::DOT},
+      {"name", query.substr(7, 4), Lexer::TokenType::TEXT},
+      {":", query.substr(11, 1), Lexer::TokenType::COMPARATOR},
+      {"foo", query.substr(12, 3), Lexer::TokenType::TEXT}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<Node> tree_root,
                              parser.ConsumeQuery());
@@ -256,11 +259,11 @@ TEST(ParserTest, HasNested) {
 }
 
 TEST(ParserTest, EmptyFunction) {
-  // Query: "foo()"
+  std::string_view query = "foo()";
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"foo", Lexer::TokenType::FUNCTION_NAME},
-      {"", Lexer::TokenType::LPAREN},
-      {"", Lexer::TokenType::RPAREN}};
+      {"foo", query.substr(0, 3), Lexer::TokenType::FUNCTION_NAME},
+      {"", query.substr(3, 1), Lexer::TokenType::LPAREN},
+      {"", query.substr(4, 1), Lexer::TokenType::RPAREN}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<Node> tree_root,
                              parser.ConsumeQuery());
@@ -279,12 +282,12 @@ TEST(ParserTest, EmptyFunction) {
 }
 
 TEST(ParserTest, FunctionSingleArg) {
-  // Query: "foo("bar")"
+  std::string_view query = "foo(\"bar\")";
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"foo", Lexer::TokenType::FUNCTION_NAME},
-      {"", Lexer::TokenType::LPAREN},
-      {"bar", Lexer::TokenType::STRING},
-      {"", Lexer::TokenType::RPAREN}};
+      {"foo", query.substr(0, 3), Lexer::TokenType::FUNCTION_NAME},
+      {"", query.substr(3, 1), Lexer::TokenType::LPAREN},
+      {"bar", query.substr(5, 3), Lexer::TokenType::STRING},
+      {"", query.substr(8, 1), Lexer::TokenType::RPAREN}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<Node> tree_root,
                              parser.ConsumeQuery());
@@ -304,11 +307,14 @@ TEST(ParserTest, FunctionSingleArg) {
 }
 
 TEST(ParserTest, FunctionMultiArg) {
-  // Query: "foo("bar", "baz")"
+  std::string_view query = "foo(\"bar\", \"baz\")";
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"foo", Lexer::TokenType::FUNCTION_NAME}, {"", Lexer::TokenType::LPAREN},
-      {"bar", Lexer::TokenType::STRING},        {"", Lexer::TokenType::COMMA},
-      {"baz", Lexer::TokenType::STRING},        {"", Lexer::TokenType::RPAREN}};
+      {"foo", query.substr(0, 3), Lexer::TokenType::FUNCTION_NAME},
+      {"", query.substr(3, 1), Lexer::TokenType::LPAREN},
+      {"bar", query.substr(5, 3), Lexer::TokenType::STRING},
+      {"", query.substr(9, 1), Lexer::TokenType::COMMA},
+      {"baz", query.substr(12, 3), Lexer::TokenType::STRING},
+      {"", query.substr(16, 1), Lexer::TokenType::RPAREN}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<Node> tree_root,
                              parser.ConsumeQuery());
@@ -329,11 +335,14 @@ TEST(ParserTest, FunctionMultiArg) {
 }
 
 TEST(ParserTest, FunctionNested) {
-  // Query: "foo(bar())"
+  std::string_view query = "foo(bar())";
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"foo", Lexer::TokenType::FUNCTION_NAME}, {"", Lexer::TokenType::LPAREN},
-      {"bar", Lexer::TokenType::FUNCTION_NAME}, {"", Lexer::TokenType::LPAREN},
-      {"", Lexer::TokenType::RPAREN},           {"", Lexer::TokenType::RPAREN}};
+      {"foo", query.substr(0, 3), Lexer::TokenType::FUNCTION_NAME},
+      {"", query.substr(3, 1), Lexer::TokenType::LPAREN},
+      {"bar", query.substr(4, 3), Lexer::TokenType::FUNCTION_NAME},
+      {"", query.substr(7, 1), Lexer::TokenType::LPAREN},
+      {"", query.substr(8, 1), Lexer::TokenType::RPAREN},
+      {"", query.substr(9, 1), Lexer::TokenType::RPAREN}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<Node> tree_root,
                              parser.ConsumeQuery());
@@ -356,13 +365,13 @@ TEST(ParserTest, FunctionNested) {
 }
 
 TEST(ParserTest, FunctionWithTrailingSequence) {
-  // Query: "foo() OR bar"
+  std::string_view query = "foo() OR bar";
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"foo", Lexer::TokenType::FUNCTION_NAME},
-      {"", Lexer::TokenType::LPAREN},
-      {"", Lexer::TokenType::RPAREN},
-      {"", Lexer::TokenType::OR},
-      {"bar", Lexer::TokenType::TEXT}};
+      {"foo", query.substr(0, 3), Lexer::TokenType::FUNCTION_NAME},
+      {"", query.substr(3, 1), Lexer::TokenType::LPAREN},
+      {"", query.substr(4, 1), Lexer::TokenType::RPAREN},
+      {"", query.substr(6, 2), Lexer::TokenType::OR},
+      {"bar", query.substr(9, 3), Lexer::TokenType::TEXT}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<Node> tree_root,
                              parser.ConsumeQuery());
@@ -386,11 +395,14 @@ TEST(ParserTest, FunctionWithTrailingSequence) {
 }
 
 TEST(ParserTest, Composite) {
-  // Query: "foo OR (bar baz)"
+  std::string_view query = "foo OR (bar baz)";
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"foo", Lexer::TokenType::TEXT}, {"", Lexer::TokenType::OR},
-      {"", Lexer::TokenType::LPAREN},  {"bar", Lexer::TokenType::TEXT},
-      {"baz", Lexer::TokenType::TEXT}, {"", Lexer::TokenType::RPAREN}};
+      {"foo", query.substr(0, 3), Lexer::TokenType::TEXT},
+      {"", query.substr(4, 2), Lexer::TokenType::OR},
+      {"", query.substr(7, 1), Lexer::TokenType::LPAREN},
+      {"bar", query.substr(8, 3), Lexer::TokenType::TEXT},
+      {"baz", query.substr(12, 3), Lexer::TokenType::TEXT},
+      {"", query.substr(15, 1), Lexer::TokenType::RPAREN}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<Node> tree_root,
                              parser.ConsumeQuery());
@@ -419,11 +431,14 @@ TEST(ParserTest, Composite) {
 }
 
 TEST(ParserTest, CompositeWithTrailingSequence) {
-  // Query: "(bar baz) OR foo"
+  std::string_view query = "(bar baz) OR foo";
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"", Lexer::TokenType::LPAREN},  {"bar", Lexer::TokenType::TEXT},
-      {"baz", Lexer::TokenType::TEXT}, {"", Lexer::TokenType::RPAREN},
-      {"", Lexer::TokenType::OR},      {"foo", Lexer::TokenType::TEXT}};
+      {"", query.substr(0, 1), Lexer::TokenType::LPAREN},
+      {"bar", query.substr(1, 3), Lexer::TokenType::TEXT},
+      {"baz", query.substr(5, 3), Lexer::TokenType::TEXT},
+      {"", query.substr(8, 1), Lexer::TokenType::RPAREN},
+      {"", query.substr(10, 2), Lexer::TokenType::OR},
+      {"foo", query.substr(13, 3), Lexer::TokenType::TEXT}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<Node> tree_root,
                              parser.ConsumeQuery());
@@ -452,17 +467,17 @@ TEST(ParserTest, CompositeWithTrailingSequence) {
 }
 
 TEST(ParserTest, Complex) {
-  // Query: "foo bar:baz OR pal("bat")"
+  std::string_view query = R"(foo bar:baz OR pal("bat"))";
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"foo", Lexer::TokenType::TEXT},
-      {"bar", Lexer::TokenType::TEXT},
-      {":", Lexer::TokenType::COMPARATOR},
-      {"baz", Lexer::TokenType::TEXT},
-      {"", Lexer::TokenType::OR},
-      {"pal", Lexer::TokenType::FUNCTION_NAME},
-      {"", Lexer::TokenType::LPAREN},
-      {"bat", Lexer::TokenType::STRING},
-      {"", Lexer::TokenType::RPAREN}};
+      {"foo", query.substr(0, 3), Lexer::TokenType::TEXT},
+      {"bar", query.substr(4, 3), Lexer::TokenType::TEXT},
+      {":", query.substr(7, 1), Lexer::TokenType::COMPARATOR},
+      {"baz", query.substr(8, 3), Lexer::TokenType::TEXT},
+      {"", query.substr(12, 2), Lexer::TokenType::OR},
+      {"pal", query.substr(15, 3), Lexer::TokenType::FUNCTION_NAME},
+      {"", query.substr(18, 1), Lexer::TokenType::LPAREN},
+      {"bat", query.substr(20, 3), Lexer::TokenType::STRING},
+      {"", query.substr(24, 1), Lexer::TokenType::RPAREN}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<Node> tree_root,
                              parser.ConsumeQuery());
@@ -498,107 +513,116 @@ TEST(ParserTest, Complex) {
 }
 
 TEST(ParserTest, InvalidHas) {
-  // Query: "foo:"  No right hand operand to :
+  std::string_view query = "foo:";  // No right hand operand to :
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"foo", Lexer::TokenType::TEXT}, {":", Lexer::TokenType::COMPARATOR}};
+      {"foo", query.substr(0, 3), Lexer::TokenType::TEXT},
+      {":", query.substr(3, 1), Lexer::TokenType::COMPARATOR}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   EXPECT_THAT(parser.ConsumeQuery(),
               StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
 }
 
 TEST(ParserTest, InvalidComposite) {
-  // Query: "(foo bar"  No terminating RPAREN
+  std::string_view query = "(foo bar";  // No terminating RPAREN
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"", Lexer::TokenType::LPAREN},
-      {"foo", Lexer::TokenType::TEXT},
-      {"bar", Lexer::TokenType::TEXT}};
+      {"", query.substr(0, 1), Lexer::TokenType::LPAREN},
+      {"foo", query.substr(1, 3), Lexer::TokenType::TEXT},
+      {"bar", query.substr(5, 3), Lexer::TokenType::TEXT}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   EXPECT_THAT(parser.ConsumeQuery(),
               StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
 }
 
 TEST(ParserTest, InvalidMember) {
-  // Query: "foo."  DOT must have succeeding TEXT
+  std::string_view query = "foo.";  // DOT must have succeeding TEXT
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"foo", Lexer::TokenType::TEXT}, {"", Lexer::TokenType::DOT}};
+      {"foo", query.substr(0, 3), Lexer::TokenType::TEXT},
+      {"", query.substr(3, 1), Lexer::TokenType::DOT}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   EXPECT_THAT(parser.ConsumeQuery(),
               StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
 }
 
 TEST(ParserTest, InvalidOr) {
-  // Query: "foo OR"   No right hand operand to OR
+  std::string_view query = "foo OR";  // No right hand operand to OR
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"foo", Lexer::TokenType::TEXT}, {"", Lexer::TokenType::OR}};
+      {"foo", query.substr(0, 3), Lexer::TokenType::TEXT},
+      {"", query.substr(3, 2), Lexer::TokenType::OR}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   EXPECT_THAT(parser.ConsumeQuery(),
               StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
 }
 
 TEST(ParserTest, InvalidAnd) {
-  // Query: "foo AND"   No right hand operand to AND
+  std::string_view query = "foo AND";  // No right hand operand to AND
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"foo", Lexer::TokenType::TEXT}, {"", Lexer::TokenType::AND}};
+      {"foo", query.substr(0, 3), Lexer::TokenType::TEXT},
+      {"", query.substr(4, 3), Lexer::TokenType::AND}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   EXPECT_THAT(parser.ConsumeQuery(),
               StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
 }
 
 TEST(ParserTest, InvalidNot) {
-  // Query: "NOT"   No right hand operand to NOT
-  std::vector<Lexer::LexerToken> lexer_tokens = {{"", Lexer::TokenType::NOT}};
+  std::string_view query = "NOT";  // No right hand operand to NOT
+  std::vector<Lexer::LexerToken> lexer_tokens = {
+      {"", query.substr(0, 3), Lexer::TokenType::NOT}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   EXPECT_THAT(parser.ConsumeQuery(),
               StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
 }
 
 TEST(ParserTest, InvalidMinus) {
-  // Query: "-"   No right hand operand to -
-  std::vector<Lexer::LexerToken> lexer_tokens = {{"", Lexer::TokenType::MINUS}};
+  std::string_view query = "-";  // No right hand operand to -
+  std::vector<Lexer::LexerToken> lexer_tokens = {
+      {"", query.substr(0, 1), Lexer::TokenType::MINUS}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   EXPECT_THAT(parser.ConsumeQuery(),
               StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
 }
 
 TEST(ParserTest, InvalidFunctionCallNoRparen) {
-  // Query: "foo("   No terminating RPAREN
+  std::string_view query = "foo(";  // No terminating RPAREN
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"foo", Lexer::TokenType::FUNCTION_NAME}, {"", Lexer::TokenType::LPAREN}};
+      {"foo", query.substr(0, 3), Lexer::TokenType::FUNCTION_NAME},
+      {"", query.substr(3, 0), Lexer::TokenType::LPAREN}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   EXPECT_THAT(parser.ConsumeQuery(),
               StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
 }
 
 TEST(ParserTest, InvalidFunctionCallNoLparen) {
-  // Query: "foo bar"   foo labeled FUNCTION_NAME despite no LPAREN
+  std::string_view query =
+      "foo bar";  // foo labeled FUNCTION_NAME despite no LPAREN
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"foo", Lexer::TokenType::FUNCTION_NAME},
-      {"bar", Lexer::TokenType::FUNCTION_NAME}};
+      {"foo", query.substr(0, 3), Lexer::TokenType::FUNCTION_NAME},
+      {"bar", query.substr(4, 3), Lexer::TokenType::FUNCTION_NAME}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   EXPECT_THAT(parser.ConsumeQuery(),
               StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
 }
 
 TEST(ParserTest, InvalidFunctionArgsHangingComma) {
-  // Query: "foo("bar",)"   no valid arg following COMMA
+  std::string_view query = R"(foo("bar",))";  // no valid arg following COMMA
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"foo", Lexer::TokenType::FUNCTION_NAME},
-      {"", Lexer::TokenType::LPAREN},
-      {"bar", Lexer::TokenType::STRING},
-      {"", Lexer::TokenType::COMMA},
-      {"", Lexer::TokenType::RPAREN}};
+      {"foo", query.substr(0, 3), Lexer::TokenType::FUNCTION_NAME},
+      {"", query.substr(3, 1), Lexer::TokenType::LPAREN},
+      {"bar", query.substr(5, 3), Lexer::TokenType::STRING},
+      {"", query.substr(9, 1), Lexer::TokenType::COMMA},
+      {"", query.substr(10, 1), Lexer::TokenType::RPAREN}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   EXPECT_THAT(parser.ConsumeQuery(),
               StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
 }
 
 TEST(ParserTest, ScoringPlus) {
-  // Scoring: "1 + 1 + 1"
-  std::vector<Lexer::LexerToken> lexer_tokens = {{"1", Lexer::TokenType::TEXT},
-                                                 {"", Lexer::TokenType::PLUS},
-                                                 {"1", Lexer::TokenType::TEXT},
-                                                 {"", Lexer::TokenType::PLUS},
-                                                 {"1", Lexer::TokenType::TEXT}};
+  std::string_view scoring_exp = "1 + 1 + 1";
+  std::vector<Lexer::LexerToken> lexer_tokens = {
+      {"1", scoring_exp.substr(0, 1), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(2, 1), Lexer::TokenType::PLUS},
+      {"1", scoring_exp.substr(4, 1), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(6, 1), Lexer::TokenType::PLUS},
+      {"1", scoring_exp.substr(8, 1), Lexer::TokenType::TEXT}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<Node> tree_root,
                              parser.ConsumeScoring());
@@ -622,12 +646,13 @@ TEST(ParserTest, ScoringPlus) {
 }
 
 TEST(ParserTest, ScoringMinus) {
-  // Scoring: "1 - 1 - 1"
-  std::vector<Lexer::LexerToken> lexer_tokens = {{"1", Lexer::TokenType::TEXT},
-                                                 {"", Lexer::TokenType::MINUS},
-                                                 {"1", Lexer::TokenType::TEXT},
-                                                 {"", Lexer::TokenType::MINUS},
-                                                 {"1", Lexer::TokenType::TEXT}};
+  std::string_view scoring_exp = "1 - 1 - 1";
+  std::vector<Lexer::LexerToken> lexer_tokens = {
+      {"1", scoring_exp.substr(0, 1), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(2, 1), Lexer::TokenType::MINUS},
+      {"1", scoring_exp.substr(4, 1), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(6, 1), Lexer::TokenType::MINUS},
+      {"1", scoring_exp.substr(8, 1), Lexer::TokenType::TEXT}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<Node> tree_root,
                              parser.ConsumeScoring());
@@ -651,11 +676,14 @@ TEST(ParserTest, ScoringMinus) {
 }
 
 TEST(ParserTest, ScoringUnaryMinus) {
-  // Scoring: "1 + -1 + 1"
+  std::string_view scoring_exp = "1 + -1 + 1";
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"1", Lexer::TokenType::TEXT}, {"", Lexer::TokenType::PLUS},
-      {"", Lexer::TokenType::MINUS}, {"1", Lexer::TokenType::TEXT},
-      {"", Lexer::TokenType::PLUS},  {"1", Lexer::TokenType::TEXT}};
+      {"1", scoring_exp.substr(0, 1), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(2, 1), Lexer::TokenType::PLUS},
+      {"", scoring_exp.substr(4, 1), Lexer::TokenType::MINUS},
+      {"1", scoring_exp.substr(5, 1), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(7, 1), Lexer::TokenType::PLUS},
+      {"1", scoring_exp.substr(9, 1), Lexer::TokenType::TEXT}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<Node> tree_root,
                              parser.ConsumeScoring());
@@ -682,12 +710,15 @@ TEST(ParserTest, ScoringUnaryMinus) {
 }
 
 TEST(ParserTest, ScoringPlusMinus) {
-  // Scoring: "11 + 12 - 13 + 14"
+  std::string_view scoring_exp = "11 + 12 - 13 + 14";
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"11", Lexer::TokenType::TEXT}, {"", Lexer::TokenType::PLUS},
-      {"12", Lexer::TokenType::TEXT}, {"", Lexer::TokenType::MINUS},
-      {"13", Lexer::TokenType::TEXT}, {"", Lexer::TokenType::PLUS},
-      {"14", Lexer::TokenType::TEXT}};
+      {"11", scoring_exp.substr(0, 2), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(3, 1), Lexer::TokenType::PLUS},
+      {"12", scoring_exp.substr(5, 2), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(6, 1), Lexer::TokenType::MINUS},
+      {"13", scoring_exp.substr(8, 2), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(11, 1), Lexer::TokenType::PLUS},
+      {"14", scoring_exp.substr(13, 2), Lexer::TokenType::TEXT}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<Node> tree_root,
                              parser.ConsumeScoring());
@@ -719,12 +750,13 @@ TEST(ParserTest, ScoringPlusMinus) {
 }
 
 TEST(ParserTest, ScoringTimes) {
-  // Scoring: "1 * 1 * 1"
-  std::vector<Lexer::LexerToken> lexer_tokens = {{"1", Lexer::TokenType::TEXT},
-                                                 {"", Lexer::TokenType::TIMES},
-                                                 {"1", Lexer::TokenType::TEXT},
-                                                 {"", Lexer::TokenType::TIMES},
-                                                 {"1", Lexer::TokenType::TEXT}};
+  std::string_view scoring_exp = "1 * 1 * 1";
+  std::vector<Lexer::LexerToken> lexer_tokens = {
+      {"1", scoring_exp.substr(0, 1), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(2, 1), Lexer::TokenType::TIMES},
+      {"1", scoring_exp.substr(4, 1), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(6, 1), Lexer::TokenType::TIMES},
+      {"1", scoring_exp.substr(8, 1), Lexer::TokenType::TEXT}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<Node> tree_root,
                              parser.ConsumeScoring());
@@ -748,12 +780,13 @@ TEST(ParserTest, ScoringTimes) {
 }
 
 TEST(ParserTest, ScoringDiv) {
-  // Scoring: "1 / 1 / 1"
-  std::vector<Lexer::LexerToken> lexer_tokens = {{"1", Lexer::TokenType::TEXT},
-                                                 {"", Lexer::TokenType::DIV},
-                                                 {"1", Lexer::TokenType::TEXT},
-                                                 {"", Lexer::TokenType::DIV},
-                                                 {"1", Lexer::TokenType::TEXT}};
+  std::string_view scoring_exp = "1 / 1 / 1";
+  std::vector<Lexer::LexerToken> lexer_tokens = {
+      {"1", scoring_exp.substr(0, 1), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(2, 1), Lexer::TokenType::DIV},
+      {"1", scoring_exp.substr(4, 1), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(6, 1), Lexer::TokenType::DIV},
+      {"1", scoring_exp.substr(8, 1), Lexer::TokenType::TEXT}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<Node> tree_root,
                              parser.ConsumeScoring());
@@ -777,13 +810,17 @@ TEST(ParserTest, ScoringDiv) {
 }
 
 TEST(ParserTest, ScoringTimesDiv) {
-  // Scoring: "11 / 12 * 13 / 14 / 15"
+  std::string_view scoring_exp = "11 / 12 * 13 / 14 / 15";
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"11", Lexer::TokenType::TEXT}, {"", Lexer::TokenType::DIV},
-      {"12", Lexer::TokenType::TEXT}, {"", Lexer::TokenType::TIMES},
-      {"13", Lexer::TokenType::TEXT}, {"", Lexer::TokenType::DIV},
-      {"14", Lexer::TokenType::TEXT}, {"", Lexer::TokenType::DIV},
-      {"15", Lexer::TokenType::TEXT}};
+      {"11", scoring_exp.substr(0, 2), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(3, 1), Lexer::TokenType::DIV},
+      {"12", scoring_exp.substr(5, 2), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(8, 1), Lexer::TokenType::TIMES},
+      {"13", scoring_exp.substr(10, 2), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(13, 1), Lexer::TokenType::DIV},
+      {"14", scoring_exp.substr(15, 2), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(18, 1), Lexer::TokenType::DIV},
+      {"15", scoring_exp.substr(20, 2), Lexer::TokenType::TEXT}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<Node> tree_root,
                              parser.ConsumeScoring());
@@ -817,29 +854,29 @@ TEST(ParserTest, ScoringTimesDiv) {
 }
 
 TEST(ParserTest, ComplexScoring) {
-  // Scoring: "1 + pow((2 * sin(3)), 4) + -5 / 6"
+  std::string_view scoring_exp = "1 + pow((2 * sin(3)), 4) + -5 / 6";
   // With parentheses in function arguments.
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"1", Lexer::TokenType::TEXT},
-      {"", Lexer::TokenType::PLUS},
-      {"pow", Lexer::TokenType::FUNCTION_NAME},
-      {"", Lexer::TokenType::LPAREN},
-      {"", Lexer::TokenType::LPAREN},
-      {"2", Lexer::TokenType::TEXT},
-      {"", Lexer::TokenType::TIMES},
-      {"sin", Lexer::TokenType::FUNCTION_NAME},
-      {"", Lexer::TokenType::LPAREN},
-      {"3", Lexer::TokenType::TEXT},
-      {"", Lexer::TokenType::RPAREN},
-      {"", Lexer::TokenType::RPAREN},
-      {"", Lexer::TokenType::COMMA},
-      {"4", Lexer::TokenType::TEXT},
-      {"", Lexer::TokenType::RPAREN},
-      {"", Lexer::TokenType::PLUS},
-      {"", Lexer::TokenType::MINUS},
-      {"5", Lexer::TokenType::TEXT},
-      {"", Lexer::TokenType::DIV},
-      {"6", Lexer::TokenType::TEXT},
+      {"1", scoring_exp.substr(0, 1), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(2, 1), Lexer::TokenType::PLUS},
+      {"pow", scoring_exp.substr(4, 3), Lexer::TokenType::FUNCTION_NAME},
+      {"", scoring_exp.substr(7, 1), Lexer::TokenType::LPAREN},
+      {"", scoring_exp.substr(8, 1), Lexer::TokenType::LPAREN},
+      {"2", scoring_exp.substr(9, 1), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(11, 1), Lexer::TokenType::TIMES},
+      {"sin", scoring_exp.substr(13, 3), Lexer::TokenType::FUNCTION_NAME},
+      {"", scoring_exp.substr(16, 1), Lexer::TokenType::LPAREN},
+      {"3", scoring_exp.substr(17, 1), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(18, 1), Lexer::TokenType::RPAREN},
+      {"", scoring_exp.substr(19, 1), Lexer::TokenType::RPAREN},
+      {"", scoring_exp.substr(20, 1), Lexer::TokenType::COMMA},
+      {"4", scoring_exp.substr(22, 1), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(23, 1), Lexer::TokenType::RPAREN},
+      {"", scoring_exp.substr(25, 1), Lexer::TokenType::PLUS},
+      {"", scoring_exp.substr(27, 1), Lexer::TokenType::MINUS},
+      {"5", scoring_exp.substr(28, 1), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(30, 1), Lexer::TokenType::DIV},
+      {"6", scoring_exp.substr(32, 1), Lexer::TokenType::TEXT},
   };
   Parser parser = Parser::Create(std::move(lexer_tokens));
   ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<Node> tree_root,
@@ -869,27 +906,27 @@ TEST(ParserTest, ComplexScoring) {
                           EqualsNodeInfo("DIV", NodeType::kNaryOperator),
                           EqualsNodeInfo("PLUS", NodeType::kNaryOperator)));
 
-  // Scoring: "1 + pow(2 * sin(3), 4) + -5 / 6"
+  scoring_exp = "1 + pow(2 * sin(3), 4) + -5 / 6";
   // Without parentheses in function arguments.
   lexer_tokens = {
-      {"1", Lexer::TokenType::TEXT},
-      {"", Lexer::TokenType::PLUS},
-      {"pow", Lexer::TokenType::FUNCTION_NAME},
-      {"", Lexer::TokenType::LPAREN},
-      {"2", Lexer::TokenType::TEXT},
-      {"", Lexer::TokenType::TIMES},
-      {"sin", Lexer::TokenType::FUNCTION_NAME},
-      {"", Lexer::TokenType::LPAREN},
-      {"3", Lexer::TokenType::TEXT},
-      {"", Lexer::TokenType::RPAREN},
-      {"", Lexer::TokenType::COMMA},
-      {"4", Lexer::TokenType::TEXT},
-      {"", Lexer::TokenType::RPAREN},
-      {"", Lexer::TokenType::PLUS},
-      {"", Lexer::TokenType::MINUS},
-      {"5", Lexer::TokenType::TEXT},
-      {"", Lexer::TokenType::DIV},
-      {"6", Lexer::TokenType::TEXT},
+      {"1", scoring_exp.substr(0, 1), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(2, 1), Lexer::TokenType::PLUS},
+      {"pow", scoring_exp.substr(4, 3), Lexer::TokenType::FUNCTION_NAME},
+      {"", scoring_exp.substr(7, 1), Lexer::TokenType::LPAREN},
+      {"2", scoring_exp.substr(8, 1), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(10, 1), Lexer::TokenType::TIMES},
+      {"sin", scoring_exp.substr(12, 3), Lexer::TokenType::FUNCTION_NAME},
+      {"", scoring_exp.substr(15, 1), Lexer::TokenType::LPAREN},
+      {"3", scoring_exp.substr(16, 1), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(17, 1), Lexer::TokenType::RPAREN},
+      {"", scoring_exp.substr(18, 1), Lexer::TokenType::COMMA},
+      {"4", scoring_exp.substr(20, 1), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(21, 1), Lexer::TokenType::RPAREN},
+      {"", scoring_exp.substr(23, 1), Lexer::TokenType::PLUS},
+      {"", scoring_exp.substr(25, 1), Lexer::TokenType::MINUS},
+      {"5", scoring_exp.substr(26, 1), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(28, 1), Lexer::TokenType::DIV},
+      {"6", scoring_exp.substr(30, 1), Lexer::TokenType::TEXT},
   };
   parser = Parser::Create(std::move(lexer_tokens));
   ICING_ASSERT_OK_AND_ASSIGN(tree_root, parser.ConsumeScoring());
@@ -899,13 +936,14 @@ TEST(ParserTest, ComplexScoring) {
 }
 
 TEST(ParserTest, ScoringMemberFunction) {
-  // Scoring: this.CreationTimestamp()
+  std::string_view scoring_exp = "this.CreationTimestamp()";
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"this", Lexer::TokenType::TEXT},
-      {"", Lexer::TokenType::DOT},
-      {"CreationTimestamp", Lexer::TokenType::FUNCTION_NAME},
-      {"", Lexer::TokenType::LPAREN},
-      {"", Lexer::TokenType::RPAREN}};
+      {"this", scoring_exp.substr(0, 4), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(4, 1), Lexer::TokenType::DOT},
+      {"CreationTimestamp", scoring_exp.substr(5, 17),
+       Lexer::TokenType::FUNCTION_NAME},
+      {"", scoring_exp.substr(22, 1), Lexer::TokenType::LPAREN},
+      {"", scoring_exp.substr(23, 1), Lexer::TokenType::RPAREN}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<Node> tree_root,
                              parser.ConsumeScoring());
@@ -927,13 +965,13 @@ TEST(ParserTest, ScoringMemberFunction) {
 }
 
 TEST(ParserTest, QueryMemberFunction) {
-  // Query: this.foo()
+  std::string_view query = "this.foo()";
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"this", Lexer::TokenType::TEXT},
-      {"", Lexer::TokenType::DOT},
-      {"foo", Lexer::TokenType::FUNCTION_NAME},
-      {"", Lexer::TokenType::LPAREN},
-      {"", Lexer::TokenType::RPAREN}};
+      {"this", query.substr(0, 4), Lexer::TokenType::TEXT},
+      {"", query.substr(4, 1), Lexer::TokenType::DOT},
+      {"foo", query.substr(5, 3), Lexer::TokenType::FUNCTION_NAME},
+      {"", query.substr(8, 1), Lexer::TokenType::LPAREN},
+      {"", query.substr(9, 1), Lexer::TokenType::RPAREN}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<Node> tree_root,
                              parser.ConsumeQuery());
@@ -954,18 +992,18 @@ TEST(ParserTest, QueryMemberFunction) {
 }
 
 TEST(ParserTest, ScoringComplexMemberFunction) {
-  // Scoring: a.b.fun(c, d)
+  std::string_view scoring_exp = "a.b.fun(c, d)";
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"a", Lexer::TokenType::TEXT},
-      {"", Lexer::TokenType::DOT},
-      {"b", Lexer::TokenType::TEXT},
-      {"", Lexer::TokenType::DOT},
-      {"fun", Lexer::TokenType::FUNCTION_NAME},
-      {"", Lexer::TokenType::LPAREN},
-      {"c", Lexer::TokenType::TEXT},
-      {"", Lexer::TokenType::COMMA},
-      {"d", Lexer::TokenType::TEXT},
-      {"", Lexer::TokenType::RPAREN}};
+      {"a", scoring_exp.substr(0, 1), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(1, 1), Lexer::TokenType::DOT},
+      {"b", scoring_exp.substr(2, 1), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(3, 1), Lexer::TokenType::DOT},
+      {"fun", scoring_exp.substr(4, 3), Lexer::TokenType::FUNCTION_NAME},
+      {"", scoring_exp.substr(7, 1), Lexer::TokenType::LPAREN},
+      {"c", scoring_exp.substr(8, 1), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(9, 1), Lexer::TokenType::COMMA},
+      {"d", scoring_exp.substr(11, 1), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(12, 1), Lexer::TokenType::RPAREN}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<Node> tree_root,
                              parser.ConsumeScoring());
@@ -993,13 +1031,18 @@ TEST(ParserTest, ScoringComplexMemberFunction) {
 }
 
 TEST(ParserTest, QueryComplexMemberFunction) {
-  // Query: this.abc.fun(def, ghi)
+  std::string_view query = "this.abc.fun(def, ghi)";
   std::vector<Lexer::LexerToken> lexer_tokens = {
-      {"this", Lexer::TokenType::TEXT},         {"", Lexer::TokenType::DOT},
-      {"abc", Lexer::TokenType::TEXT},          {"", Lexer::TokenType::DOT},
-      {"fun", Lexer::TokenType::FUNCTION_NAME}, {"", Lexer::TokenType::LPAREN},
-      {"def", Lexer::TokenType::TEXT},          {"", Lexer::TokenType::COMMA},
-      {"ghi", Lexer::TokenType::TEXT},          {"", Lexer::TokenType::RPAREN}};
+      {"this", query.substr(0, 4), Lexer::TokenType::TEXT},
+      {"", query.substr(4, 1), Lexer::TokenType::DOT},
+      {"abc", query.substr(5, 3), Lexer::TokenType::TEXT},
+      {"", query.substr(8, 1), Lexer::TokenType::DOT},
+      {"fun", query.substr(9, 3), Lexer::TokenType::FUNCTION_NAME},
+      {"", query.substr(12, 1), Lexer::TokenType::LPAREN},
+      {"def", query.substr(13, 3), Lexer::TokenType::TEXT},
+      {"", query.substr(16, 1), Lexer::TokenType::COMMA},
+      {"ghi", query.substr(17, 3), Lexer::TokenType::TEXT},
+      {"", query.substr(20, 1), Lexer::TokenType::RPAREN}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   ICING_ASSERT_OK_AND_ASSIGN(std::unique_ptr<Node> tree_root,
                              parser.ConsumeQuery());
@@ -1027,11 +1070,12 @@ TEST(ParserTest, QueryComplexMemberFunction) {
 }
 
 TEST(ParserTest, InvalidScoringToken) {
-  // Scoring: "1 + NOT 1"
-  std::vector<Lexer::LexerToken> lexer_tokens = {{"1", Lexer::TokenType::TEXT},
-                                                 {"", Lexer::TokenType::PLUS},
-                                                 {"", Lexer::TokenType::NOT},
-                                                 {"1", Lexer::TokenType::TEXT}};
+  std::string_view scoring_exp = "1 + NOT 1";
+  std::vector<Lexer::LexerToken> lexer_tokens = {
+      {"1", scoring_exp.substr(0, 1), Lexer::TokenType::TEXT},
+      {"", scoring_exp.substr(2, 1), Lexer::TokenType::PLUS},
+      {"", scoring_exp.substr(4, 3), Lexer::TokenType::NOT},
+      {"1", scoring_exp.substr(8, 1), Lexer::TokenType::TEXT}};
   Parser parser = Parser::Create(std::move(lexer_tokens));
   EXPECT_THAT(parser.ConsumeScoring(),
               StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
diff --git a/icing/query/advanced_query_parser/pending-value.cc b/icing/query/advanced_query_parser/pending-value.cc
index 903e12f..67bdc3a 100644
--- a/icing/query/advanced_query_parser/pending-value.cc
+++ b/icing/query/advanced_query_parser/pending-value.cc
@@ -36,7 +36,7 @@ libtextclassifier3::Status PendingValue::ParseInt() {
         "Unable to parse \"", query_term_.term, "\" as number."));
   }
   data_type_ = DataType::kLong;
-  query_term_ = {"", false};
+  query_term_ = {/*term=*/"", /*raw_term=*/"", /*is_prefix_val=*/false};
   return libtextclassifier3::Status::OK;
 }
 
diff --git a/icing/query/advanced_query_parser/pending-value.h b/icing/query/advanced_query_parser/pending-value.h
index d18789d..1a6717e 100644
--- a/icing/query/advanced_query_parser/pending-value.h
+++ b/icing/query/advanced_query_parser/pending-value.h
@@ -38,17 +38,18 @@ enum class DataType {
 
 struct QueryTerm {
   std::string term;
+  std::string_view raw_term;
   bool is_prefix_val;
 };
 
 // A holder for intermediate results when processing child nodes.
 struct PendingValue {
-  static PendingValue CreateStringPendingValue(QueryTerm query_term) {
-    return PendingValue(std::move(query_term), DataType::kString);
+  static PendingValue CreateStringPendingValue(QueryTerm str) {
+    return PendingValue(std::move(str), DataType::kString);
   }
 
-  static PendingValue CreateTextPendingValue(QueryTerm query_term) {
-    return PendingValue(std::move(query_term), DataType::kText);
+  static PendingValue CreateTextPendingValue(QueryTerm text) {
+    return PendingValue(std::move(text), DataType::kText);
   }
 
   PendingValue() : data_type_(DataType::kNone) {}
@@ -125,7 +126,7 @@ struct PendingValue {
 
  private:
   explicit PendingValue(QueryTerm query_term, DataType data_type)
-      : query_term_({std::move(query_term)}), data_type_(data_type) {}
+      : query_term_(std::move(query_term)), data_type_(data_type) {}
 
   libtextclassifier3::Status CheckDataType(DataType required_data_type) const {
     if (data_type_ == required_data_type) {
@@ -141,7 +142,7 @@ struct PendingValue {
   // iterator_ will be populated when data_type_ is kDocumentIterator.
   std::unique_ptr<DocHitInfoIterator> iterator_;
 
-  // string_vals_ will be populated when data_type_ is kStringList.
+  // string_vals_ will be populated when data_type_ kStringList.
   std::vector<std::string> string_vals_;
 
   // query_term_ will be populated when data_type_ is kString or kText
diff --git a/icing/query/advanced_query_parser/query-visitor.cc b/icing/query/advanced_query_parser/query-visitor.cc
index a1a9c38..31223a5 100644
--- a/icing/query/advanced_query_parser/query-visitor.cc
+++ b/icing/query/advanced_query_parser/query-visitor.cc
@@ -37,9 +37,12 @@
 #include "icing/query/advanced_query_parser/lexer.h"
 #include "icing/query/advanced_query_parser/param.h"
 #include "icing/query/advanced_query_parser/parser.h"
+#include "icing/query/advanced_query_parser/pending-value.h"
+#include "icing/query/advanced_query_parser/util/string-util.h"
 #include "icing/query/query-features.h"
 #include "icing/schema/property-util.h"
 #include "icing/schema/section.h"
+#include "icing/tokenization/token.h"
 #include "icing/tokenization/tokenizer.h"
 #include "icing/util/status-macros.h"
 
@@ -54,32 +57,13 @@ struct CreateList {
     std::vector<std::string> values;
     values.reserve(args.size());
     for (PendingValue& arg : args) {
-      QueryTerm val = std::move(arg).string_val().ValueOrDie();
-      values.push_back(std::move(val.term));
+      QueryTerm string_val = std::move(arg).string_val().ValueOrDie();
+      values.push_back(std::move(string_val.term));
     }
     return PendingValue(std::move(values));
   }
 };
 
-libtextclassifier3::StatusOr<std::string> UnescapeStringValue(
-    std::string_view value) {
-  std::string result;
-  bool in_escape = false;
-  for (char c : value) {
-    if (in_escape) {
-      in_escape = false;
-    } else if (c == '\\') {
-      in_escape = true;
-      continue;
-    } else if (c == '"') {
-      return absl_ports::InvalidArgumentError(
-          "Encountered an unescaped quotation mark!");
-    }
-    result += c;
-  }
-  return result;
-}
-
 bool IsNumericComparator(std::string_view operator_text) {
   if (operator_text.length() < 1 || operator_text.length() > 2) {
     return false;
@@ -168,8 +152,14 @@ void QueryVisitor::PendingPropertyRestricts::AddValidRestricts(
 }
 
 libtextclassifier3::StatusOr<std::unique_ptr<DocHitInfoIterator>>
-QueryVisitor::CreateTermIterator(QueryTerm query_term) {
+QueryVisitor::CreateTermIterator(const QueryTerm& query_term) {
+  if (query_term.is_prefix_val) {
+    // '*' prefix operator was added in list filters
+    features_.insert(kListFilterQueryLanguageFeature);
+  }
   TermMatchType::Code match_type = GetTermMatchType(query_term.is_prefix_val);
+  int unnormalized_term_start =
+      query_term.raw_term.data() - raw_query_text_.data();
   if (!processing_not_) {
     // 1. Add term to property_query_terms_map
     if (pending_property_restricts_.has_active_property_restricts()) {
@@ -183,13 +173,11 @@ QueryVisitor::CreateTermIterator(QueryTerm query_term) {
 
     // 2. If needed add term iterator to query_term_iterators_ map.
     if (needs_term_frequency_info_) {
-    // TODO(b/152934343) Save "term start index" into Node and PendingValue and
-    // pass it into index.GetIterator
       ICING_ASSIGN_OR_RETURN(
           std::unique_ptr<DocHitInfoIterator> term_iterator,
-          index_.GetIterator(query_term.term, /*term_start_index=*/0,
-                             /*unnormalized_term_length=*/0, kSectionIdMaskAll,
-                             match_type, needs_term_frequency_info_));
+          index_.GetIterator(query_term.term, unnormalized_term_start,
+                             query_term.raw_term.length(), kSectionIdMaskAll,
+                             match_type_, needs_term_frequency_info_));
       query_term_iterators_[query_term.term] =
           std::make_unique<DocHitInfoIteratorFilter>(
               std::move(term_iterator), &document_store_, &schema_store_,
@@ -198,10 +186,8 @@ QueryVisitor::CreateTermIterator(QueryTerm query_term) {
   }
 
   // 3. Add the term iterator.
-  // TODO(b/152934343) Save "term start index" into Node and PendingValue and
-  // pass it into index.GetIterator
-  return index_.GetIterator(query_term.term, /*term_start_index=*/0,
-                            /*unnormalized_term_length=*/0, kSectionIdMaskAll,
+  return index_.GetIterator(query_term.term, unnormalized_term_start,
+                            query_term.raw_term.length(), kSectionIdMaskAll,
                             match_type, needs_term_frequency_info_);
 }
 
@@ -266,7 +252,7 @@ libtextclassifier3::StatusOr<PendingValue> QueryVisitor::SearchFunction(
   } else {
     QueryVisitor query_visitor(&index_, &numeric_index_, &document_store_,
                                &schema_store_, &normalizer_, &tokenizer_,
-                               filter_options_, match_type_,
+                               query->raw_term, filter_options_, match_type_,
                                needs_term_frequency_info_,
                                pending_property_restricts_, processing_not_);
     tree_root->Accept(&query_visitor);
@@ -353,24 +339,44 @@ QueryVisitor::PopPendingIterator() {
     // The tokenizer will produce 1+ tokens out of the text. The prefix operator
     // only applies to the final token.
     bool reached_final_token = !token_itr->Advance();
+    // raw_text is the portion of text_value.raw_term that hasn't yet been
+    // matched to any of the tokens that we've processed. escaped_token will
+    // hold the portion of raw_text that corresponds to the current token that
+    // is being processed.
+    std::string_view raw_text = text_value.raw_term;
+    std::string_view raw_token;
     while (!reached_final_token) {
       std::vector<Token> tokens = token_itr->GetTokens();
-      reached_final_token = !token_itr->Advance();
+      if (tokens.size() > 1) {
+        // The tokenizer iterator iterates between token groups. In practice,
+        // the tokenizer used with QueryVisitor (PlainTokenizer) will always
+        // only produce a single token per token group.
+        return absl_ports::InvalidArgumentError(
+            "Encountered unexpected token group with >1 tokens.");
+      }
 
-      // The tokenizer iterator iterates between token groups. In practice, the
-      // tokenizer used with QueryVisitor (PlainTokenizer) will always only
-      // produce a single token per token group.
-      // For simplicity, we will apply the prefix operator to *all* tokens
-      // in the final token group.
-      for (const Token& token : tokens) {
-        normalized_term = normalizer_.NormalizeTerm(token.text);
-        ICING_ASSIGN_OR_RETURN(
-            std::unique_ptr<DocHitInfoIterator> iterator,
-            CreateTermIterator(
-                QueryTerm{std::move(normalized_term),
-                          reached_final_token && text_value.is_prefix_val}));
-        iterators.push_back(std::move(iterator));
+      reached_final_token = !token_itr->Advance();
+      const Token& token = tokens.at(0);
+      if (reached_final_token && token.text.length() == raw_text.length()) {
+        // Unescaped tokens are strictly smaller than their escaped counterparts
+        // This means that if we're at the final token and token.length equals
+        // raw_text, then all of raw_text must correspond to this token.
+        raw_token = raw_text;
+      } else {
+        ICING_ASSIGN_OR_RETURN(raw_token, string_util::FindEscapedToken(
+                                                  raw_text, token.text));
       }
+      normalized_term = normalizer_.NormalizeTerm(token.text);
+      QueryTerm term_value{std::move(normalized_term), raw_token,
+                           reached_final_token && text_value.is_prefix_val};
+      ICING_ASSIGN_OR_RETURN(std::unique_ptr<DocHitInfoIterator> iterator,
+                             CreateTermIterator(std::move(term_value)));
+      iterators.push_back(std::move(iterator));
+
+      // Remove escaped_token from raw_text now that we've processed
+      // raw_text.
+      const char* escaped_token_end = raw_token.data() + raw_token.length();
+      raw_text = raw_text.substr(escaped_token_end - raw_text.data());
     }
 
     // Finally, create an And Iterator. If there's only a single term here, then
@@ -452,7 +458,8 @@ libtextclassifier3::Status QueryVisitor::ProcessNumericComparator(
                          GetInt64Range(node->operator_text(), int_value));
   ICING_ASSIGN_OR_RETURN(
       std::unique_ptr<DocHitInfoIterator> iterator,
-      numeric_index_.GetIterator(text_value.term, range.low, range.high));
+      numeric_index_.GetIterator(text_value.term, range.low, range.high,
+                                 document_store_, schema_store_));
 
   features_.insert(kNumericSearchFeature);
   pending_values_.push(PendingValue(std::move(iterator)));
@@ -618,22 +625,23 @@ void QueryVisitor::VisitFunctionName(const FunctionNameNode* node) {
 
 void QueryVisitor::VisitString(const StringNode* node) {
   // A STRING node can only be a term. Create the iterator now.
-  auto unescaped_string_or = UnescapeStringValue(node->value());
+  auto unescaped_string_or = string_util::UnescapeStringValue(node->value());
   if (!unescaped_string_or.ok()) {
     pending_error_ = std::move(unescaped_string_or).status();
     return;
   }
   std::string unescaped_string = std::move(unescaped_string_or).ValueOrDie();
-  pending_values_.push(PendingValue::CreateStringPendingValue(
-      QueryTerm{std::move(unescaped_string), node->is_prefix()}));
+  QueryTerm val{std::move(unescaped_string), node->raw_value(),
+                node->is_prefix()};
+  pending_values_.push(PendingValue::CreateStringPendingValue(std::move(val)));
 }
 
 void QueryVisitor::VisitText(const TextNode* node) {
   // TEXT nodes could either be a term (and will become DocHitInfoIteratorTerm)
   // or a property name. As such, we just push the TEXT value into pending
   // values and determine which it is at a later point.
-  pending_values_.push(PendingValue::CreateTextPendingValue(
-      QueryTerm{std::move(node->value()), node->is_prefix()}));
+  QueryTerm val{std::move(node->value()), node->raw_value(), node->is_prefix()};
+  pending_values_.push(PendingValue::CreateTextPendingValue(std::move(val)));
 }
 
 void QueryVisitor::VisitMember(const MemberNode* node) {
@@ -668,6 +676,8 @@ void QueryVisitor::VisitMember(const MemberNode* node) {
     libtextclassifier3::StatusOr<QueryTerm> member_or;
     std::vector<std::string> members;
     QueryTerm text_val;
+    const char* start = nullptr;
+    const char* end = nullptr;
     while (!pending_values_.empty() &&
            !pending_values_.top().is_placeholder()) {
       member_or = PopPendingTextValue();
@@ -681,11 +691,19 @@ void QueryVisitor::VisitMember(const MemberNode* node) {
             "Cannot use prefix operator '*' within a property name!");
         return;
       }
+      if (start == nullptr) {
+        start = text_val.raw_term.data();
+        end = text_val.raw_term.data() + text_val.raw_term.length();
+      } else {
+        start = std::min(start, text_val.raw_term.data());
+        end = std::max(end, text_val.raw_term.data() + text_val.raw_term.length());
+      }
       members.push_back(std::move(text_val.term));
     }
     QueryTerm member;
     member.term = absl_ports::StrJoin(members.rbegin(), members.rend(),
                                       property_util::kPropertyPathSeparator);
+    member.raw_term = std::string_view(start, end - start);
     member.is_prefix_val = false;
     pending_value = PendingValue::CreateTextPendingValue(std::move(member));
   }
@@ -739,6 +757,9 @@ void QueryVisitor::VisitFunction(const FunctionNode* node) {
   // 5. Pop placeholder in pending_values and add the result of our function.
   pending_values_.pop();
   pending_values_.push(std::move(eval_result).ValueOrDie());
+
+  // Support for custom functions was added in list filters.
+  features_.insert(kListFilterQueryLanguageFeature);
 }
 
 // TODO(b/265312785) Clarify handling of the interaction between HAS and NOT.
@@ -771,6 +792,15 @@ void QueryVisitor::VisitUnaryOperator(const UnaryOperatorNode* node) {
   if (!status.ok()) {
     pending_error_ = std::move(status);
   }
+
+  if (!is_minus ||
+      pending_property_restricts_.has_active_property_restricts() ||
+      processing_not_) {
+    // 'NOT' operator was added in list filters.
+    // Likewise, mixing property restricts and NOTs were made valid in list
+    // filters.
+    features_.insert(kListFilterQueryLanguageFeature);
+  }
 }
 
 void QueryVisitor::VisitNaryOperator(const NaryOperatorNode* node) {
@@ -780,6 +810,13 @@ void QueryVisitor::VisitNaryOperator(const NaryOperatorNode* node) {
     return;
   }
 
+  if (pending_property_restricts_.has_active_property_restricts() ||
+      processing_not_) {
+    // Likewise, mixing property restricts and NOT with compound statements was
+    // added in list filters.
+    features_.insert(kListFilterQueryLanguageFeature);
+  }
+
   if (node->operator_text() == ":") {
     libtextclassifier3::Status status = ProcessHasOperator(node);
     if (!status.ok()) {
diff --git a/icing/query/advanced_query_parser/query-visitor.h b/icing/query/advanced_query_parser/query-visitor.h
index 7498457..9fcaec0 100644
--- a/icing/query/advanced_query_parser/query-visitor.h
+++ b/icing/query/advanced_query_parser/query-visitor.h
@@ -49,12 +49,12 @@ class QueryVisitor : public AbstractSyntaxTreeVisitor {
       Index* index, const NumericIndex<int64_t>* numeric_index,
       const DocumentStore* document_store, const SchemaStore* schema_store,
       const Normalizer* normalizer, const Tokenizer* tokenizer,
+      std::string_view raw_query_text,
       DocHitInfoIteratorFilter::Options filter_options,
       TermMatchType::Code match_type, bool needs_term_frequency_info)
       : QueryVisitor(index, numeric_index, document_store, schema_store,
-                     normalizer, tokenizer, filter_options, match_type,
-                     needs_term_frequency_info,
-
+                     normalizer, tokenizer, raw_query_text, filter_options,
+                     match_type, needs_term_frequency_info,
                      PendingPropertyRestricts(),
                      /*processing_not=*/false) {}
 
@@ -105,9 +105,9 @@ class QueryVisitor : public AbstractSyntaxTreeVisitor {
       Index* index, const NumericIndex<int64_t>* numeric_index,
       const DocumentStore* document_store, const SchemaStore* schema_store,
       const Normalizer* normalizer, const Tokenizer* tokenizer,
+      std::string_view raw_query_text,
       DocHitInfoIteratorFilter::Options filter_options,
       TermMatchType::Code match_type, bool needs_term_frequency_info,
-
       PendingPropertyRestricts pending_property_restricts, bool processing_not)
       : index_(*index),
         numeric_index_(*numeric_index),
@@ -115,6 +115,7 @@ class QueryVisitor : public AbstractSyntaxTreeVisitor {
         schema_store_(*schema_store),
         normalizer_(*normalizer),
         tokenizer_(*tokenizer),
+        raw_query_text_(raw_query_text),
         filter_options_(std::move(filter_options)),
         match_type_(match_type),
         needs_term_frequency_info_(needs_term_frequency_info),
@@ -133,7 +134,7 @@ class QueryVisitor : public AbstractSyntaxTreeVisitor {
   //   - On success, a DocHitInfoIterator for the provided term
   //   - INVALID_ARGUMENT if unable to create an iterator for the term.
   libtextclassifier3::StatusOr<std::unique_ptr<DocHitInfoIterator>>
-  CreateTermIterator(QueryTerm term);
+  CreateTermIterator(const QueryTerm& term);
 
   // Processes the PendingValue at the top of pending_values_, parses it into a
   // int64_t and pops the top.
@@ -279,6 +280,7 @@ class QueryVisitor : public AbstractSyntaxTreeVisitor {
   const Normalizer& normalizer_;                // Does not own!
   const Tokenizer& tokenizer_;                  // Does not own!
 
+  std::string_view raw_query_text_;
   DocHitInfoIteratorFilter::Options filter_options_;
   TermMatchType::Code match_type_;
   // Whether or not term_frequency information is needed. This affects:
diff --git a/icing/query/advanced_query_parser/query-visitor_test.cc b/icing/query/advanced_query_parser/query-visitor_test.cc
index 033e86b..b560d52 100644
--- a/icing/query/advanced_query_parser/query-visitor_test.cc
+++ b/icing/query/advanced_query_parser/query-visitor_test.cc
@@ -17,6 +17,7 @@
 #include <cstdint>
 #include <limits>
 #include <memory>
+#include <string_view>
 
 #include "icing/text_classifier/lib3/utils/base/status.h"
 #include "gmock/gmock.h"
@@ -225,14 +226,20 @@ TEST_P(QueryVisitorTest, SimpleLessThan) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use,
-              ElementsAre(kNumericSearchFeature));
+  if (GetParam() == QueryType::kSearch) {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kNumericSearchFeature,
+                                     kListFilterQueryLanguageFeature));
+  } else {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kNumericSearchFeature));
+  }
   // "price" is a property restrict here and "2" isn't a "term" - its a numeric
   // value. So QueryTermIterators should be empty.
   EXPECT_THAT(ExtractKeys(query_results.query_term_iterators), IsEmpty());
@@ -262,14 +269,20 @@ TEST_P(QueryVisitorTest, SimpleLessThanEq) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use,
-              ElementsAre(kNumericSearchFeature));
+  if (GetParam() == QueryType::kSearch) {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kNumericSearchFeature,
+                                     kListFilterQueryLanguageFeature));
+  } else {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kNumericSearchFeature));
+  }
   // "price" is a property restrict here and "1" isn't a "term" - its a numeric
   // value. So QueryTermIterators should be empty.
   EXPECT_THAT(ExtractKeys(query_results.query_term_iterators), IsEmpty());
@@ -299,14 +312,20 @@ TEST_P(QueryVisitorTest, SimpleEqual) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use,
-              ElementsAre(kNumericSearchFeature));
+  if (GetParam() == QueryType::kSearch) {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kNumericSearchFeature,
+                                     kListFilterQueryLanguageFeature));
+  } else {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kNumericSearchFeature));
+  }
   // "price" is a property restrict here and "2" isn't a "term" - its a numeric
   // value. So QueryTermIterators should be empty.
   EXPECT_THAT(ExtractKeys(query_results.query_term_iterators), IsEmpty());
@@ -336,14 +355,20 @@ TEST_P(QueryVisitorTest, SimpleGreaterThanEq) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use,
-              ElementsAre(kNumericSearchFeature));
+  if (GetParam() == QueryType::kSearch) {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kNumericSearchFeature,
+                                     kListFilterQueryLanguageFeature));
+  } else {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kNumericSearchFeature));
+  }
   // "price" is a property restrict here and "1" isn't a "term" - its a numeric
   // value. So QueryTermIterators should be empty.
   EXPECT_THAT(ExtractKeys(query_results.query_term_iterators), IsEmpty());
@@ -373,14 +398,20 @@ TEST_P(QueryVisitorTest, SimpleGreaterThan) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use,
-              ElementsAre(kNumericSearchFeature));
+  if (GetParam() == QueryType::kSearch) {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kNumericSearchFeature,
+                                     kListFilterQueryLanguageFeature));
+  } else {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kNumericSearchFeature));
+  }
   // "price" is a property restrict here and "1" isn't a "term" - its a numeric
   // value. So QueryTermIterators should be empty.
   EXPECT_THAT(ExtractKeys(query_results.query_term_iterators), IsEmpty());
@@ -411,14 +442,20 @@ TEST_P(QueryVisitorTest, IntMinLessThanEqual) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use,
-              ElementsAre(kNumericSearchFeature));
+  if (GetParam() == QueryType::kSearch) {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kNumericSearchFeature,
+                                     kListFilterQueryLanguageFeature));
+  } else {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kNumericSearchFeature));
+  }
   // "price" is a property restrict here and int_min isn't a "term" - its a
   // numeric value. So QueryTermIterators should be empty.
   EXPECT_THAT(ExtractKeys(query_results.query_term_iterators), IsEmpty());
@@ -449,14 +486,20 @@ TEST_P(QueryVisitorTest, IntMaxGreaterThanEqual) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use,
-              ElementsAre(kNumericSearchFeature));
+  if (GetParam() == QueryType::kSearch) {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kNumericSearchFeature,
+                                     kListFilterQueryLanguageFeature));
+  } else {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kNumericSearchFeature));
+  }
   // "price" is a property restrict here and int_max isn't a "term" - its a
   // numeric value. So QueryTermIterators should be empty.
   EXPECT_THAT(ExtractKeys(query_results.query_term_iterators), IsEmpty());
@@ -488,14 +531,20 @@ TEST_P(QueryVisitorTest, NestedPropertyLessThan) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use,
-              ElementsAre(kNumericSearchFeature));
+  if (GetParam() == QueryType::kSearch) {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kNumericSearchFeature,
+                                     kListFilterQueryLanguageFeature));
+  } else {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kNumericSearchFeature));
+  }
   // "subscription.price" is a property restrict here and int_max isn't a "term"
   // - its a numeric value. So QueryTermIterators should be empty.
   EXPECT_THAT(ExtractKeys(query_results.query_term_iterators), IsEmpty());
@@ -510,7 +559,7 @@ TEST_P(QueryVisitorTest, IntParsingError) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
@@ -524,7 +573,7 @@ TEST_P(QueryVisitorTest, NotEqualsUnsupported) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
@@ -552,16 +601,19 @@ TEST_P(QueryVisitorTest, LessThanTooManyOperandsInvalid) {
 
   // Create an invalid AST for the query '3 < subscription.price 25' where '<'
   // has three operands
-  auto property_node = std::make_unique<TextNode>("subscription");
-  auto subproperty_node = std::make_unique<TextNode>("price");
+  std::string_view query = "3 < subscription.price 25";
+  auto property_node =
+      std::make_unique<TextNode>("subscription", query.substr(4, 12));
+  auto subproperty_node =
+      std::make_unique<TextNode>("price", query.substr(17, 5));
   std::vector<std::unique_ptr<TextNode>> member_args;
   member_args.push_back(std::move(property_node));
   member_args.push_back(std::move(subproperty_node));
   auto member_node = std::make_unique<MemberNode>(std::move(member_args),
                                                   /*function=*/nullptr);
 
-  auto value_node = std::make_unique<TextNode>("3");
-  auto extra_value_node = std::make_unique<TextNode>("25");
+  auto value_node = std::make_unique<TextNode>("3", query.substr(0, 1));
+  auto extra_value_node = std::make_unique<TextNode>("25", query.substr(23, 2));
   std::vector<std::unique_ptr<Node>> args;
   args.push_back(std::move(value_node));
   args.push_back(std::move(member_node));
@@ -569,7 +621,7 @@ TEST_P(QueryVisitorTest, LessThanTooManyOperandsInvalid) {
   auto root_node = std::make_unique<NaryOperatorNode>("<", std::move(args));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
@@ -580,8 +632,11 @@ TEST_P(QueryVisitorTest, LessThanTooManyOperandsInvalid) {
 TEST_P(QueryVisitorTest, LessThanTooFewOperandsInvalid) {
   // Create an invalid AST for the query 'subscription.price <' where '<'
   // has a single operand
-  auto property_node = std::make_unique<TextNode>("subscription");
-  auto subproperty_node = std::make_unique<TextNode>("price");
+  std::string_view query = "subscription.price <";
+  auto property_node =
+      std::make_unique<TextNode>("subscription", query.substr(0, 12));
+  auto subproperty_node =
+      std::make_unique<TextNode>("price", query.substr(13, 5));
   std::vector<std::unique_ptr<TextNode>> member_args;
   member_args.push_back(std::move(property_node));
   member_args.push_back(std::move(subproperty_node));
@@ -593,7 +648,7 @@ TEST_P(QueryVisitorTest, LessThanTooFewOperandsInvalid) {
   auto root_node = std::make_unique<NaryOperatorNode>("<", std::move(args));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
@@ -624,14 +679,20 @@ TEST_P(QueryVisitorTest, LessThanNonExistentPropertyNotFound) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use,
-              ElementsAre(kNumericSearchFeature));
+  if (GetParam() == QueryType::kSearch) {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kNumericSearchFeature,
+                                     kListFilterQueryLanguageFeature));
+  } else {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kNumericSearchFeature));
+  }
   EXPECT_THAT(ExtractKeys(query_results.query_term_iterators), IsEmpty());
   EXPECT_THAT(query_results.query_terms, IsEmpty());
   EXPECT_THAT(GetDocumentIds(query_results.root_iterator.get()), IsEmpty());
@@ -640,7 +701,7 @@ TEST_P(QueryVisitorTest, LessThanNonExistentPropertyNotFound) {
 TEST_P(QueryVisitorTest, NeverVisitedReturnsInvalid) {
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), "",
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   EXPECT_THAT(std::move(query_visitor).ConsumeResults(),
@@ -669,7 +730,7 @@ TEST_P(QueryVisitorTest, IntMinLessThanInvalid) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
@@ -699,7 +760,7 @@ TEST_P(QueryVisitorTest, IntMaxGreaterThanInvalid) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
@@ -714,7 +775,7 @@ TEST_P(QueryVisitorTest, NumericComparisonPropertyStringIsInvalid) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
@@ -776,14 +837,20 @@ TEST_P(QueryVisitorTest, NumericComparatorDoesntAffectLaterTerms) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use,
-              ElementsAre(kNumericSearchFeature));
+  if (GetParam() == QueryType::kSearch) {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kNumericSearchFeature,
+                                     kListFilterQueryLanguageFeature));
+  } else {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kNumericSearchFeature));
+  }
   EXPECT_THAT(ExtractKeys(query_results.query_term_iterators), IsEmpty());
   EXPECT_THAT(query_results.query_terms, IsEmpty());
   EXPECT_THAT(GetDocumentIds(query_results.root_iterator.get()),
@@ -813,7 +880,7 @@ TEST_P(QueryVisitorTest, SingleTermTermFrequencyEnabled) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
@@ -865,7 +932,7 @@ TEST_P(QueryVisitorTest, SingleTermTermFrequencyDisabled) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/false);
   root_node->Accept(&query_visitor);
@@ -917,7 +984,7 @@ TEST_P(QueryVisitorTest, SingleTermPrefix) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_EXACT,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
@@ -933,7 +1000,7 @@ TEST_P(QueryVisitorTest, SingleTermPrefix) {
   ICING_ASSERT_OK_AND_ASSIGN(root_node, ParseQueryHelper(query));
   QueryVisitor query_visitor_two(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_EXACT,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor_two);
@@ -953,7 +1020,7 @@ TEST_P(QueryVisitorTest, PrefixOperatorAfterPropertyReturnsInvalid) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
@@ -967,7 +1034,7 @@ TEST_P(QueryVisitorTest, PrefixOperatorAfterNumericValueReturnsInvalid) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
@@ -981,7 +1048,7 @@ TEST_P(QueryVisitorTest, PrefixOperatorAfterPropertyRestrictReturnsInvalid) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
@@ -1019,7 +1086,7 @@ TEST_P(QueryVisitorTest, SegmentationWithPrefix) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_EXACT,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
@@ -1042,7 +1109,7 @@ TEST_P(QueryVisitorTest, SegmentationWithPrefix) {
   ICING_ASSERT_OK_AND_ASSIGN(root_node, ParseQueryHelper(query));
   QueryVisitor query_visitor_two(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_EXACT,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor_two);
@@ -1079,14 +1146,20 @@ TEST_P(QueryVisitorTest, SingleVerbatimTerm) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use,
-              ElementsAre(kVerbatimSearchFeature));
+  if (GetParam() == QueryType::kSearch) {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kVerbatimSearchFeature,
+                                     kListFilterQueryLanguageFeature));
+  } else {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kVerbatimSearchFeature));
+  }
   EXPECT_THAT(ExtractKeys(query_results.query_terms), UnorderedElementsAre(""));
   EXPECT_THAT(query_results.query_terms[""],
               UnorderedElementsAre("foo:bar(baz)"));
@@ -1120,14 +1193,15 @@ TEST_P(QueryVisitorTest, SingleVerbatimTermPrefix) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_EXACT,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
   EXPECT_THAT(query_results.features_in_use,
-              ElementsAre(kVerbatimSearchFeature));
+              UnorderedElementsAre(kVerbatimSearchFeature,
+                                   kListFilterQueryLanguageFeature));
   EXPECT_THAT(ExtractKeys(query_results.query_terms), UnorderedElementsAre(""));
   EXPECT_THAT(query_results.query_terms[""], UnorderedElementsAre("foo:bar("));
   EXPECT_THAT(ExtractKeys(query_results.query_term_iterators),
@@ -1172,14 +1246,20 @@ TEST_P(QueryVisitorTest, VerbatimTermEscapingQuote) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use,
-              ElementsAre(kVerbatimSearchFeature));
+  if (GetParam() == QueryType::kSearch) {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kVerbatimSearchFeature,
+                                     kListFilterQueryLanguageFeature));
+  } else {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kVerbatimSearchFeature));
+  }
   EXPECT_THAT(ExtractKeys(query_results.query_terms), UnorderedElementsAre(""));
   EXPECT_THAT(query_results.query_terms[""],
               UnorderedElementsAre(R"(foobar")"));
@@ -1218,14 +1298,20 @@ TEST_P(QueryVisitorTest, VerbatimTermEscapingEscape) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use,
-              ElementsAre(kVerbatimSearchFeature));
+  if (GetParam() == QueryType::kSearch) {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kVerbatimSearchFeature,
+                                     kListFilterQueryLanguageFeature));
+  } else {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kVerbatimSearchFeature));
+  }
   EXPECT_THAT(ExtractKeys(query_results.query_terms), UnorderedElementsAre(""));
   EXPECT_THAT(query_results.query_terms[""],
               UnorderedElementsAre(R"(foobar\)"));
@@ -1266,14 +1352,20 @@ TEST_P(QueryVisitorTest, VerbatimTermEscapingNonSpecialChar) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use,
-              ElementsAre(kVerbatimSearchFeature));
+  if (GetParam() == QueryType::kSearch) {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kVerbatimSearchFeature,
+                                     kListFilterQueryLanguageFeature));
+  } else {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kVerbatimSearchFeature));
+  }
   EXPECT_THAT(ExtractKeys(query_results.query_terms), UnorderedElementsAre(""));
   EXPECT_THAT(query_results.query_terms[""],
               UnorderedElementsAre(R"(foobary)"));
@@ -1287,14 +1379,20 @@ TEST_P(QueryVisitorTest, VerbatimTermEscapingNonSpecialChar) {
   ICING_ASSERT_OK_AND_ASSIGN(root_node, ParseQueryHelper(query));
   QueryVisitor query_visitor_two(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor_two);
   ICING_ASSERT_OK_AND_ASSIGN(query_results,
                              std::move(query_visitor_two).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use,
-              ElementsAre(kVerbatimSearchFeature));
+  if (GetParam() == QueryType::kSearch) {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kVerbatimSearchFeature,
+                                     kListFilterQueryLanguageFeature));
+  } else {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kVerbatimSearchFeature));
+  }
   EXPECT_THAT(ExtractKeys(query_results.query_terms), UnorderedElementsAre(""));
   EXPECT_THAT(query_results.query_terms[""],
               UnorderedElementsAre(R"(foobar\y)"));
@@ -1336,14 +1434,20 @@ TEST_P(QueryVisitorTest, VerbatimTermNewLine) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use,
-              ElementsAre(kVerbatimSearchFeature));
+  if (GetParam() == QueryType::kSearch) {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kVerbatimSearchFeature,
+                                     kListFilterQueryLanguageFeature));
+  } else {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kVerbatimSearchFeature));
+  }
   EXPECT_THAT(ExtractKeys(query_results.query_terms), UnorderedElementsAre(""));
   EXPECT_THAT(query_results.query_terms[""], UnorderedElementsAre("foobar\n"));
   EXPECT_THAT(ExtractKeys(query_results.query_term_iterators),
@@ -1356,14 +1460,20 @@ TEST_P(QueryVisitorTest, VerbatimTermNewLine) {
   ICING_ASSERT_OK_AND_ASSIGN(root_node, ParseQueryHelper(query));
   QueryVisitor query_visitor_two(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor_two);
   ICING_ASSERT_OK_AND_ASSIGN(query_results,
                              std::move(query_visitor_two).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use,
-              ElementsAre(kVerbatimSearchFeature));
+  if (GetParam() == QueryType::kSearch) {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kVerbatimSearchFeature,
+                                     kListFilterQueryLanguageFeature));
+  } else {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kVerbatimSearchFeature));
+  }
   EXPECT_THAT(ExtractKeys(query_results.query_terms), UnorderedElementsAre(""));
   EXPECT_THAT(query_results.query_terms[""],
               UnorderedElementsAre(R"(foobar\n)"));
@@ -1399,14 +1509,20 @@ TEST_P(QueryVisitorTest, VerbatimTermEscapingComplex) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use,
-              ElementsAre(kVerbatimSearchFeature));
+  if (GetParam() == QueryType::kSearch) {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kVerbatimSearchFeature,
+                                     kListFilterQueryLanguageFeature));
+  } else {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kVerbatimSearchFeature));
+  }
   EXPECT_THAT(ExtractKeys(query_results.query_terms), UnorderedElementsAre(""));
   EXPECT_THAT(query_results.query_terms[""],
               UnorderedElementsAre(R"(foo\"bar\nbaz")"));
@@ -1450,7 +1566,7 @@ TEST_P(QueryVisitorTest, SingleMinusTerm) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
@@ -1458,7 +1574,12 @@ TEST_P(QueryVisitorTest, SingleMinusTerm) {
                              std::move(query_visitor).ConsumeResults());
   EXPECT_THAT(ExtractKeys(query_results.query_terms), IsEmpty());
   EXPECT_THAT(query_results.query_term_iterators, IsEmpty());
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  if (GetParam() == QueryType::kSearch) {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kListFilterQueryLanguageFeature));
+  } else {
+    EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  }
   EXPECT_THAT(GetDocumentIds(query_results.root_iterator.get()),
               ElementsAre(kDocumentId2));
 }
@@ -1497,14 +1618,15 @@ TEST_P(QueryVisitorTest, SingleNotTerm) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
   EXPECT_THAT(query_results.query_terms, IsEmpty());
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  EXPECT_THAT(query_results.features_in_use,
+              UnorderedElementsAre(kListFilterQueryLanguageFeature));
   EXPECT_THAT(query_results.query_term_iterators, IsEmpty());
   EXPECT_THAT(GetDocumentIds(query_results.root_iterator.get()),
               ElementsAre(kDocumentId2));
@@ -1549,13 +1671,14 @@ TEST_P(QueryVisitorTest, NestedNotTerms) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  EXPECT_THAT(query_results.features_in_use,
+              UnorderedElementsAre(kListFilterQueryLanguageFeature));
   EXPECT_THAT(ExtractKeys(query_results.query_terms), UnorderedElementsAre(""));
   EXPECT_THAT(query_results.query_terms[""],
               UnorderedElementsAre("foo", "baz"));
@@ -1615,13 +1738,14 @@ TEST_P(QueryVisitorTest, DeeplyNestedNotTerms) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  EXPECT_THAT(query_results.features_in_use,
+              UnorderedElementsAre(kListFilterQueryLanguageFeature));
   EXPECT_THAT(ExtractKeys(query_results.query_terms), UnorderedElementsAre(""));
   EXPECT_THAT(query_results.query_terms[""],
               UnorderedElementsAre("bar", "baz", "bat"));
@@ -1653,13 +1777,18 @@ TEST_P(QueryVisitorTest, ImplicitAndTerms) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  if (GetParam() == QueryType::kSearch) {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kListFilterQueryLanguageFeature));
+  } else {
+    EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  }
   EXPECT_THAT(ExtractKeys(query_results.query_terms), UnorderedElementsAre(""));
   EXPECT_THAT(query_results.query_terms[""],
               UnorderedElementsAre("foo", "bar"));
@@ -1691,13 +1820,18 @@ TEST_P(QueryVisitorTest, ExplicitAndTerms) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  if (GetParam() == QueryType::kSearch) {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kListFilterQueryLanguageFeature));
+  } else {
+    EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  }
   EXPECT_THAT(ExtractKeys(query_results.query_terms), UnorderedElementsAre(""));
   EXPECT_THAT(query_results.query_terms[""],
               UnorderedElementsAre("foo", "bar"));
@@ -1729,13 +1863,18 @@ TEST_P(QueryVisitorTest, OrTerms) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  if (GetParam() == QueryType::kSearch) {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kListFilterQueryLanguageFeature));
+  } else {
+    EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  }
   EXPECT_THAT(ExtractKeys(query_results.query_terms), UnorderedElementsAre(""));
   EXPECT_THAT(query_results.query_terms[""],
               UnorderedElementsAre("foo", "bar"));
@@ -1769,13 +1908,18 @@ TEST_P(QueryVisitorTest, AndOrTermPrecedence) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  if (GetParam() == QueryType::kSearch) {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kListFilterQueryLanguageFeature));
+  } else {
+    EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  }
   EXPECT_THAT(ExtractKeys(query_results.query_terms), UnorderedElementsAre(""));
   EXPECT_THAT(query_results.query_terms[""],
               UnorderedElementsAre("foo", "bar", "baz"));
@@ -1789,13 +1933,18 @@ TEST_P(QueryVisitorTest, AndOrTermPrecedence) {
   ICING_ASSERT_OK_AND_ASSIGN(root_node, ParseQueryHelper(query));
   QueryVisitor query_visitor_two(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor_two);
   ICING_ASSERT_OK_AND_ASSIGN(query_results,
                              std::move(query_visitor_two).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  if (GetParam() == QueryType::kSearch) {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kListFilterQueryLanguageFeature));
+  } else {
+    EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  }
   EXPECT_THAT(ExtractKeys(query_results.query_terms), UnorderedElementsAre(""));
   EXPECT_THAT(query_results.query_terms[""],
               UnorderedElementsAre("foo", "bar", "baz"));
@@ -1808,13 +1957,18 @@ TEST_P(QueryVisitorTest, AndOrTermPrecedence) {
   ICING_ASSERT_OK_AND_ASSIGN(root_node, ParseQueryHelper(query));
   QueryVisitor query_visitor_three(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor_three);
   ICING_ASSERT_OK_AND_ASSIGN(query_results,
                              std::move(query_visitor_three).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  if (GetParam() == QueryType::kSearch) {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kListFilterQueryLanguageFeature));
+  } else {
+    EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  }
   EXPECT_THAT(ExtractKeys(query_results.query_terms), UnorderedElementsAre(""));
   EXPECT_THAT(query_results.query_terms[""],
               UnorderedElementsAre("foo", "bar", "baz"));
@@ -1863,13 +2017,14 @@ TEST_P(QueryVisitorTest, AndOrNotPrecedence) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  EXPECT_THAT(query_results.features_in_use,
+              UnorderedElementsAre(kListFilterQueryLanguageFeature));
   EXPECT_THAT(ExtractKeys(query_results.query_terms), UnorderedElementsAre(""));
   EXPECT_THAT(query_results.query_terms[""],
               UnorderedElementsAre("foo", "baz"));
@@ -1882,13 +2037,14 @@ TEST_P(QueryVisitorTest, AndOrNotPrecedence) {
   ICING_ASSERT_OK_AND_ASSIGN(root_node, ParseQueryHelper(query));
   QueryVisitor query_visitor_two(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor_two);
   ICING_ASSERT_OK_AND_ASSIGN(query_results,
                              std::move(query_visitor_two).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  EXPECT_THAT(query_results.features_in_use,
+              UnorderedElementsAre(kListFilterQueryLanguageFeature));
   EXPECT_THAT(ExtractKeys(query_results.query_terms), UnorderedElementsAre(""));
   EXPECT_THAT(query_results.query_terms[""], UnorderedElementsAre("foo"));
   EXPECT_THAT(ExtractKeys(query_results.query_term_iterators),
@@ -1943,7 +2099,7 @@ TEST_P(QueryVisitorTest, PropertyFilter) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
@@ -1954,7 +2110,12 @@ TEST_P(QueryVisitorTest, PropertyFilter) {
   EXPECT_THAT(query_results.query_terms["prop1"], UnorderedElementsAre("foo"));
   EXPECT_THAT(ExtractKeys(query_results.query_term_iterators),
               UnorderedElementsAre("foo"));
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  if (GetParam() == QueryType::kSearch) {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kListFilterQueryLanguageFeature));
+  } else {
+    EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  }
   EXPECT_THAT(GetDocumentIds(query_results.root_iterator.get()),
               ElementsAre(kDocumentId1, kDocumentId0));
 }
@@ -2011,7 +2172,7 @@ TEST_F(QueryVisitorTest, MultiPropertyFilter) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
@@ -2023,7 +2184,8 @@ TEST_F(QueryVisitorTest, MultiPropertyFilter) {
   EXPECT_THAT(query_results.query_terms["prop2"], UnorderedElementsAre("foo"));
   EXPECT_THAT(ExtractKeys(query_results.query_term_iterators),
               UnorderedElementsAre("foo"));
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  EXPECT_THAT(query_results.features_in_use,
+              UnorderedElementsAre(kListFilterQueryLanguageFeature));
   EXPECT_THAT(GetDocumentIds(query_results.root_iterator.get()),
               ElementsAre(kDocumentId1, kDocumentId0));
 }
@@ -2051,7 +2213,7 @@ TEST_P(QueryVisitorTest, PropertyFilterStringIsInvalid) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
@@ -2105,7 +2267,7 @@ TEST_P(QueryVisitorTest, PropertyFilterNonNormalized) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
@@ -2116,7 +2278,12 @@ TEST_P(QueryVisitorTest, PropertyFilterNonNormalized) {
   EXPECT_THAT(query_results.query_terms["PROP1"], UnorderedElementsAre("foo"));
   EXPECT_THAT(ExtractKeys(query_results.query_term_iterators),
               UnorderedElementsAre("foo"));
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  if (GetParam() == QueryType::kSearch) {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kListFilterQueryLanguageFeature));
+  } else {
+    EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  }
   EXPECT_THAT(GetDocumentIds(query_results.root_iterator.get()),
               ElementsAre(kDocumentId1, kDocumentId0));
 }
@@ -2168,13 +2335,14 @@ TEST_P(QueryVisitorTest, PropertyFilterWithGrouping) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  EXPECT_THAT(query_results.features_in_use,
+              UnorderedElementsAre(kListFilterQueryLanguageFeature));
   EXPECT_THAT(ExtractKeys(query_results.query_terms),
               UnorderedElementsAre("prop1"));
   EXPECT_THAT(query_results.query_terms["prop1"],
@@ -2231,13 +2399,14 @@ TEST_P(QueryVisitorTest, ValidNestedPropertyFilter) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  EXPECT_THAT(query_results.features_in_use,
+              UnorderedElementsAre(kListFilterQueryLanguageFeature));
   EXPECT_THAT(ExtractKeys(query_results.query_terms),
               UnorderedElementsAre("prop1"));
   EXPECT_THAT(query_results.query_terms["prop1"], UnorderedElementsAre("foo"));
@@ -2251,13 +2420,14 @@ TEST_P(QueryVisitorTest, ValidNestedPropertyFilter) {
   ICING_ASSERT_OK_AND_ASSIGN(root_node, ParseQueryHelper(query));
   QueryVisitor query_visitor_two(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor_two);
   ICING_ASSERT_OK_AND_ASSIGN(query_results,
                              std::move(query_visitor_two).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  EXPECT_THAT(query_results.features_in_use,
+              UnorderedElementsAre(kListFilterQueryLanguageFeature));
   EXPECT_THAT(ExtractKeys(query_results.query_terms),
               UnorderedElementsAre("prop1"));
   EXPECT_THAT(query_results.query_terms["prop1"], UnorderedElementsAre("foo"));
@@ -2313,13 +2483,14 @@ TEST_P(QueryVisitorTest, InvalidNestedPropertyFilter) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  EXPECT_THAT(query_results.features_in_use,
+              UnorderedElementsAre(kListFilterQueryLanguageFeature));
   EXPECT_THAT(ExtractKeys(query_results.query_terms), IsEmpty());
   EXPECT_THAT(ExtractKeys(query_results.query_term_iterators), IsEmpty());
   EXPECT_THAT(GetDocumentIds(query_results.root_iterator.get()), IsEmpty());
@@ -2333,13 +2504,14 @@ TEST_P(QueryVisitorTest, InvalidNestedPropertyFilter) {
   ICING_ASSERT_OK_AND_ASSIGN(root_node, ParseQueryHelper(query));
   QueryVisitor query_visitor_two(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor_two);
   ICING_ASSERT_OK_AND_ASSIGN(query_results,
                              std::move(query_visitor_two).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  EXPECT_THAT(query_results.features_in_use,
+              UnorderedElementsAre(kListFilterQueryLanguageFeature));
   EXPECT_THAT(ExtractKeys(query_results.query_terms), IsEmpty());
   EXPECT_THAT(ExtractKeys(query_results.query_term_iterators), IsEmpty());
   EXPECT_THAT(GetDocumentIds(query_results.root_iterator.get()), IsEmpty());
@@ -2395,13 +2567,14 @@ TEST_P(QueryVisitorTest, NotWithPropertyFilter) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  EXPECT_THAT(query_results.features_in_use,
+              UnorderedElementsAre(kListFilterQueryLanguageFeature));
   EXPECT_THAT(ExtractKeys(query_results.query_terms), IsEmpty());
   EXPECT_THAT(query_results.query_term_iterators, IsEmpty());
   EXPECT_THAT(GetDocumentIds(query_results.root_iterator.get()),
@@ -2415,13 +2588,14 @@ TEST_P(QueryVisitorTest, NotWithPropertyFilter) {
   ICING_ASSERT_OK_AND_ASSIGN(root_node, ParseQueryHelper(query));
   QueryVisitor query_visitor_two(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor_two);
   ICING_ASSERT_OK_AND_ASSIGN(query_results,
                              std::move(query_visitor_two).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  EXPECT_THAT(query_results.features_in_use,
+              UnorderedElementsAre(kListFilterQueryLanguageFeature));
   EXPECT_THAT(ExtractKeys(query_results.query_terms), IsEmpty());
   EXPECT_THAT(query_results.query_term_iterators, IsEmpty());
   EXPECT_THAT(GetDocumentIds(query_results.root_iterator.get()),
@@ -2478,14 +2652,15 @@ TEST_P(QueryVisitorTest, PropertyFilterWithNot) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
 
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  EXPECT_THAT(query_results.features_in_use,
+              UnorderedElementsAre(kListFilterQueryLanguageFeature));
   EXPECT_THAT(ExtractKeys(query_results.query_terms),
               UnorderedElementsAre("prop1"));
   EXPECT_THAT(query_results.query_terms["prop1"], UnorderedElementsAre("bar"));
@@ -2501,13 +2676,14 @@ TEST_P(QueryVisitorTest, PropertyFilterWithNot) {
   ICING_ASSERT_OK_AND_ASSIGN(root_node, ParseQueryHelper(query));
   QueryVisitor query_visitor_two(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor_two);
   ICING_ASSERT_OK_AND_ASSIGN(query_results,
                              std::move(query_visitor_two).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  EXPECT_THAT(query_results.features_in_use,
+              UnorderedElementsAre(kListFilterQueryLanguageFeature));
   EXPECT_THAT(ExtractKeys(query_results.query_terms),
               UnorderedElementsAre("prop1"));
   EXPECT_THAT(query_results.query_terms["prop1"], UnorderedElementsAre("bar"));
@@ -2579,13 +2755,18 @@ TEST_P(QueryVisitorTest, SegmentationTest) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  if (GetParam() == QueryType::kSearch) {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kListFilterQueryLanguageFeature));
+  } else {
+    EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  }
   EXPECT_THAT(ExtractKeys(query_results.query_terms), UnorderedElementsAre(""));
   if (IsCfStringTokenization()) {
     EXPECT_THAT(query_results.query_terms[""],
@@ -2692,13 +2873,18 @@ TEST_P(QueryVisitorTest, PropertyRestrictsPopCorrectly) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  if (GetParam() == QueryType::kSearch) {
+    EXPECT_THAT(query_results.features_in_use,
+                UnorderedElementsAre(kListFilterQueryLanguageFeature));
+  } else {
+    EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  }
   EXPECT_THAT(ExtractKeys(query_results.query_terms),
               UnorderedElementsAre("", "prop1"));
   EXPECT_THAT(query_results.query_terms[""],
@@ -2802,13 +2988,14 @@ TEST_P(QueryVisitorTest, UnsatisfiablePropertyRestrictsPopCorrectly) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  EXPECT_THAT(query_results.features_in_use,
+              UnorderedElementsAre(kListFilterQueryLanguageFeature));
   EXPECT_THAT(ExtractKeys(query_results.query_terms),
               UnorderedElementsAre("prop0", "prop2"));
   EXPECT_THAT(query_results.query_terms["prop0"], UnorderedElementsAre("val0"));
@@ -2825,7 +3012,7 @@ TEST_F(QueryVisitorTest, UnsupportedFunctionReturnsInvalidArgument) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
@@ -2839,7 +3026,7 @@ TEST_F(QueryVisitorTest, SearchFunctionTooFewArgumentsReturnsInvalidArgument) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
@@ -2853,7 +3040,7 @@ TEST_F(QueryVisitorTest, SearchFunctionTooManyArgumentsReturnsInvalidArgument) {
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
@@ -2869,7 +3056,7 @@ TEST_F(QueryVisitorTest,
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
@@ -2881,7 +3068,7 @@ TEST_F(QueryVisitorTest,
   ICING_ASSERT_OK_AND_ASSIGN(root_node, ParseQueryHelper(query));
   QueryVisitor query_visitor_two(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor_two);
@@ -2897,7 +3084,7 @@ TEST_F(QueryVisitorTest,
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
@@ -2909,7 +3096,7 @@ TEST_F(QueryVisitorTest,
   ICING_ASSERT_OK_AND_ASSIGN(root_node, ParseQueryHelper(query));
   QueryVisitor query_visitor_two(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor_two);
@@ -2924,7 +3111,7 @@ TEST_F(QueryVisitorTest,
                              ParseQueryHelper(query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
@@ -2984,14 +3171,15 @@ TEST_F(QueryVisitorTest, SearchFunctionNestedFunctionCalls) {
                              ParseQueryHelper(level_two_query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), level_two_query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
 
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  EXPECT_THAT(query_results.features_in_use,
+              UnorderedElementsAre(kListFilterQueryLanguageFeature));
   EXPECT_THAT(ExtractKeys(query_results.query_terms),
               UnorderedElementsAre("prop1"));
   EXPECT_THAT(query_results.query_terms["prop1"],
@@ -3008,13 +3196,14 @@ TEST_F(QueryVisitorTest, SearchFunctionNestedFunctionCalls) {
   QueryVisitor query_visitor_two(
       index_.get(), numeric_index_.get(), document_store_.get(),
       schema_store_.get(), normalizer_.get(), tokenizer_.get(),
-      DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
+      level_three_query, DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor_two);
   ICING_ASSERT_OK_AND_ASSIGN(query_results,
                              std::move(query_visitor_two).ConsumeResults());
 
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  EXPECT_THAT(query_results.features_in_use,
+              UnorderedElementsAre(kListFilterQueryLanguageFeature));
   EXPECT_THAT(ExtractKeys(query_results.query_terms),
               UnorderedElementsAre("prop1"));
   EXPECT_THAT(query_results.query_terms["prop1"],
@@ -3031,13 +3220,14 @@ TEST_F(QueryVisitorTest, SearchFunctionNestedFunctionCalls) {
   QueryVisitor query_visitor_three(
       index_.get(), numeric_index_.get(), document_store_.get(),
       schema_store_.get(), normalizer_.get(), tokenizer_.get(),
-      DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
+      level_four_query, DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor_three);
   ICING_ASSERT_OK_AND_ASSIGN(query_results,
                              std::move(query_visitor_three).ConsumeResults());
 
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  EXPECT_THAT(query_results.features_in_use,
+              UnorderedElementsAre(kListFilterQueryLanguageFeature));
   EXPECT_THAT(ExtractKeys(query_results.query_terms),
               UnorderedElementsAre("prop1"));
   EXPECT_THAT(query_results.query_terms["prop1"],
@@ -3148,14 +3338,15 @@ TEST_F(QueryVisitorTest, SearchFunctionNestedPropertyRestrictsNarrowing) {
                              ParseQueryHelper(level_one_query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), level_one_query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
 
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  EXPECT_THAT(query_results.features_in_use,
+              UnorderedElementsAre(kListFilterQueryLanguageFeature));
   EXPECT_THAT(ExtractKeys(query_results.query_terms),
               UnorderedElementsAre("prop0", "prop1", "prop2", "prop3", "prop4",
                                    "prop5", "prop6", "prop7"));
@@ -3179,14 +3370,15 @@ TEST_F(QueryVisitorTest, SearchFunctionNestedPropertyRestrictsNarrowing) {
   ICING_ASSERT_OK_AND_ASSIGN(root_node, ParseQueryHelper(level_two_query));
   QueryVisitor query_visitor_two(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), level_two_query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor_two);
   ICING_ASSERT_OK_AND_ASSIGN(query_results,
                              std::move(query_visitor_two).ConsumeResults());
 
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  EXPECT_THAT(query_results.features_in_use,
+              UnorderedElementsAre(kListFilterQueryLanguageFeature));
   EXPECT_THAT(ExtractKeys(query_results.query_terms),
               UnorderedElementsAre("prop0", "prop2", "prop4", "prop6"));
   EXPECT_THAT(query_results.query_terms["prop0"], UnorderedElementsAre("foo"));
@@ -3205,13 +3397,14 @@ TEST_F(QueryVisitorTest, SearchFunctionNestedPropertyRestrictsNarrowing) {
   QueryVisitor query_visitor_three(
       index_.get(), numeric_index_.get(), document_store_.get(),
       schema_store_.get(), normalizer_.get(), tokenizer_.get(),
-      DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
+      level_three_query, DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor_three);
   ICING_ASSERT_OK_AND_ASSIGN(query_results,
                              std::move(query_visitor_three).ConsumeResults());
 
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  EXPECT_THAT(query_results.features_in_use,
+              UnorderedElementsAre(kListFilterQueryLanguageFeature));
   EXPECT_THAT(ExtractKeys(query_results.query_terms),
               UnorderedElementsAre("prop0", "prop6"));
   EXPECT_THAT(query_results.query_terms["prop0"], UnorderedElementsAre("foo"));
@@ -3224,7 +3417,7 @@ TEST_F(QueryVisitorTest, SearchFunctionNestedPropertyRestrictsNarrowing) {
 
 // This test will nest `search` calls together with the set of restricts
 // narrowing at each level so that the set of docs matching the query shrinks.
-TEST_F(QueryVisitorTest, SearchFunctionNestedPropertyRestrictsExpandinging) {
+TEST_F(QueryVisitorTest, SearchFunctionNestedPropertyRestrictsExpanding) {
   PropertyConfigProto prop =
       PropertyConfigBuilder()
           .SetName("prop0")
@@ -3322,14 +3515,15 @@ TEST_F(QueryVisitorTest, SearchFunctionNestedPropertyRestrictsExpandinging) {
                              ParseQueryHelper(level_one_query));
   QueryVisitor query_visitor(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), level_one_query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor);
   ICING_ASSERT_OK_AND_ASSIGN(QueryResults query_results,
                              std::move(query_visitor).ConsumeResults());
 
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  EXPECT_THAT(query_results.features_in_use,
+              UnorderedElementsAre(kListFilterQueryLanguageFeature));
   EXPECT_THAT(ExtractKeys(query_results.query_terms),
               UnorderedElementsAre("prop0", "prop6"));
   EXPECT_THAT(query_results.query_terms["prop0"], UnorderedElementsAre("foo"));
@@ -3345,14 +3539,15 @@ TEST_F(QueryVisitorTest, SearchFunctionNestedPropertyRestrictsExpandinging) {
   ICING_ASSERT_OK_AND_ASSIGN(root_node, ParseQueryHelper(level_two_query));
   QueryVisitor query_visitor_two(
       index_.get(), numeric_index_.get(), document_store_.get(),
-      schema_store_.get(), normalizer_.get(), tokenizer_.get(),
+      schema_store_.get(), normalizer_.get(), tokenizer_.get(), level_two_query,
       DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor_two);
   ICING_ASSERT_OK_AND_ASSIGN(query_results,
                              std::move(query_visitor_two).ConsumeResults());
 
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  EXPECT_THAT(query_results.features_in_use,
+              UnorderedElementsAre(kListFilterQueryLanguageFeature));
   EXPECT_THAT(ExtractKeys(query_results.query_terms),
               UnorderedElementsAre("prop0", "prop6"));
   EXPECT_THAT(query_results.query_terms["prop0"], UnorderedElementsAre("foo"));
@@ -3370,13 +3565,14 @@ TEST_F(QueryVisitorTest, SearchFunctionNestedPropertyRestrictsExpandinging) {
   QueryVisitor query_visitor_three(
       index_.get(), numeric_index_.get(), document_store_.get(),
       schema_store_.get(), normalizer_.get(), tokenizer_.get(),
-      DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
+      level_three_query, DocHitInfoIteratorFilter::Options(), TERM_MATCH_PREFIX,
       /*needs_term_frequency_info_=*/true);
   root_node->Accept(&query_visitor_three);
   ICING_ASSERT_OK_AND_ASSIGN(query_results,
                              std::move(query_visitor_three).ConsumeResults());
 
-  EXPECT_THAT(query_results.features_in_use, IsEmpty());
+  EXPECT_THAT(query_results.features_in_use,
+              UnorderedElementsAre(kListFilterQueryLanguageFeature));
   EXPECT_THAT(ExtractKeys(query_results.query_terms),
               UnorderedElementsAre("prop0", "prop6"));
   EXPECT_THAT(query_results.query_terms["prop0"], UnorderedElementsAre("foo"));
diff --git a/icing/query/advanced_query_parser/util/string-util.cc b/icing/query/advanced_query_parser/util/string-util.cc
new file mode 100644
index 0000000..9af2ed6
--- /dev/null
+++ b/icing/query/advanced_query_parser/util/string-util.cc
@@ -0,0 +1,106 @@
+// Copyright (C) 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "icing/query/advanced_query_parser/util/string-util.h"
+
+#include "icing/absl_ports/canonical_errors.h"
+#include "icing/absl_ports/str_cat.h"
+
+namespace icing {
+namespace lib {
+
+namespace string_util {
+
+libtextclassifier3::StatusOr<std::string> UnescapeStringValue(
+    std::string_view value) {
+  std::string result;
+  bool in_escape = false;
+  for (char c : value) {
+    if (in_escape) {
+      in_escape = false;
+    } else if (c == '\\') {
+      in_escape = true;
+      continue;
+    } else if (c == '"') {
+      return absl_ports::InvalidArgumentError(
+          "Encountered an unescaped quotation mark!");
+    }
+    result += c;
+  }
+  return result;
+}
+
+libtextclassifier3::StatusOr<std::string_view> FindEscapedToken(
+    std::string_view escaped_string, std::string_view unescaped_token) {
+  if (unescaped_token.empty()) {
+    return absl_ports::InvalidArgumentError(
+        "Cannot find escaped token in empty unescaped token.");
+  }
+
+  // Find the start of unescaped_token within the escaped_string
+  const char* esc_string_end = escaped_string.data() + escaped_string.length();
+  size_t pos = escaped_string.find(unescaped_token[0]);
+  const char* esc_token_start = (pos == std::string_view::npos)
+                                    ? esc_string_end
+                                    : escaped_string.data() + pos;
+  const char* esc_token_cur = esc_token_start;
+  const char* possible_next_start = nullptr;
+  bool is_escaped = false;
+  int i = 0;
+  for (; i < unescaped_token.length() && esc_token_cur < esc_string_end;
+       ++esc_token_cur) {
+    if (esc_token_cur != esc_token_start &&
+        *esc_token_cur == unescaped_token[0] &&
+        possible_next_start == nullptr) {
+      possible_next_start = esc_token_cur;
+    }
+
+    // Every char in unescaped_token should either be an escape or match the
+    // next char in unescaped_token.
+    if (!is_escaped && *esc_token_cur == '\\') {
+      is_escaped = true;
+    } else if (*esc_token_cur == unescaped_token[i]) {
+      is_escaped = false;
+      ++i;
+    } else {
+      // No match. If we don't have a possible_next_start, then try to find one.
+      if (possible_next_start == nullptr) {
+        pos = escaped_string.find(unescaped_token[0],
+                                  esc_token_cur - escaped_string.data());
+        if (pos == std::string_view::npos) {
+          break;
+        }
+        esc_token_start = escaped_string.data() + pos;
+      } else {
+        esc_token_start = possible_next_start;
+        possible_next_start = nullptr;
+      }
+      // esc_token_start has been reset to a char that equals unescaped_token[0]
+      // The for loop above will advance esc_token_cur so set i to 1.
+      i = 1;
+      esc_token_cur = esc_token_start;
+    }
+  }
+  if (i != unescaped_token.length()) {
+    return absl_ports::InvalidArgumentError(
+        absl_ports::StrCat("Couldn't match chars at token=", unescaped_token,
+                           ") and raw_text=", escaped_string));
+  }
+  return std::string_view(esc_token_start, esc_token_cur - esc_token_start);
+}
+
+}  // namespace string_util
+
+}  // namespace lib
+}  // namespace icing
\ No newline at end of file
diff --git a/icing/query/advanced_query_parser/util/string-util.h b/icing/query/advanced_query_parser/util/string-util.h
new file mode 100644
index 0000000..09fb451
--- /dev/null
+++ b/icing/query/advanced_query_parser/util/string-util.h
@@ -0,0 +1,49 @@
+// Copyright (C) 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ICING_QUERY_ADVANCED_QUERY_PARSER__STRING_UTIL_H_
+#define ICING_QUERY_ADVANCED_QUERY_PARSER__STRING_UTIL_H_
+
+#include <string>
+#include <string_view>
+
+#include "icing/text_classifier/lib3/utils/base/statusor.h"
+
+namespace icing {
+namespace lib {
+
+namespace string_util {
+
+// Returns:
+//   - On success, value with the escapes removed.
+//   - INVALID_ARGUMENT if an non-escaped quote is encountered.
+//  Ex. "fo\\\\o" -> "fo\\o"
+libtextclassifier3::StatusOr<std::string> UnescapeStringValue(
+    std::string_view value);
+
+// Returns:
+//   - On success, string_view pointing to the segment of escaped_string that,
+//     if unescaped, would match unescaped_token.
+//   - INVALID_ARGUMENT
+//  Ex. escaped_string="foo b\\a\\\"r baz", unescaped_token="ba\"r"
+//      returns "b\\a\\\"r"
+libtextclassifier3::StatusOr<std::string_view> FindEscapedToken(
+    std::string_view escaped_string, std::string_view unescaped_token);
+
+}  // namespace string_util
+
+}  // namespace lib
+}  // namespace icing
+
+#endif  // ICING_QUERY_ADVANCED_QUERY_PARSER__STRING_UTIL_H_
diff --git a/icing/query/advanced_query_parser/util/string-util_test.cc b/icing/query/advanced_query_parser/util/string-util_test.cc
new file mode 100644
index 0000000..a7ccf3e
--- /dev/null
+++ b/icing/query/advanced_query_parser/util/string-util_test.cc
@@ -0,0 +1,125 @@
+// Copyright (C) 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "icing/query/advanced_query_parser/util/string-util.h"
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include "icing/testing/common-matchers.h"
+
+namespace icing {
+namespace lib {
+
+namespace {
+
+using ::testing::Eq;
+using ::testing::IsEmpty;
+
+TEST(StringUtilTest, UnescapeStringEmptyString) {
+  EXPECT_THAT(string_util::UnescapeStringValue(""), IsOkAndHolds(IsEmpty()));
+}
+
+TEST(StringUtilTest, UnescapeStringStringWithNoEscapes) {
+  EXPECT_THAT(string_util::UnescapeStringValue("foo"), IsOkAndHolds("foo"));
+  EXPECT_THAT(string_util::UnescapeStringValue("f o o"), IsOkAndHolds("f o o"));
+  EXPECT_THAT(string_util::UnescapeStringValue("f\to\to"),
+              IsOkAndHolds("f\to\to"));
+  EXPECT_THAT(string_util::UnescapeStringValue("f.o.o"), IsOkAndHolds("f.o.o"));
+}
+
+TEST(StringUtilTest, UnescapeStringStringWithEscapes) {
+  EXPECT_THAT(string_util::UnescapeStringValue("f\\oo"), IsOkAndHolds("foo"));
+  EXPECT_THAT(string_util::UnescapeStringValue("f\\\\oo"),
+              IsOkAndHolds("f\\oo"));
+  EXPECT_THAT(string_util::UnescapeStringValue("f\\\"oo"),
+              IsOkAndHolds("f\"oo"));
+  EXPECT_THAT(string_util::UnescapeStringValue("foo\\"), IsOkAndHolds("foo"));
+  EXPECT_THAT(string_util::UnescapeStringValue("foo b\\a\\\"r baz"),
+              IsOkAndHolds("foo ba\"r baz"));
+  EXPECT_THAT(string_util::UnescapeStringValue("bar b\\aar bar\\s bart"),
+              IsOkAndHolds("bar baar bars bart"));
+  EXPECT_THAT(string_util::UnescapeStringValue("\\\\\\\\a"),
+              IsOkAndHolds("\\\\a"));
+}
+
+TEST(StringUtilTest, UnescapeStringQuoteWithoutEscape) {
+  EXPECT_THAT(string_util::UnescapeStringValue("f\\o\"o"),
+              StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
+  EXPECT_THAT(string_util::UnescapeStringValue("f\"oo"),
+              StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
+}
+
+TEST(StringUtilTest, FindEscapedTokenEmptyUnescapedToken) {
+  EXPECT_THAT(string_util::FindEscapedToken("foo b\\a\\\"r baz", ""),
+              StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
+}
+
+TEST(StringUtilTest, FindEscapedTokenTokenNotPresent) {
+  EXPECT_THAT(string_util::FindEscapedToken("foo b\\a\\\"r baz", "elephant"),
+              StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
+  EXPECT_THAT(string_util::FindEscapedToken("foo b\\a\\\"r baz", "bat"),
+              StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
+  EXPECT_THAT(string_util::FindEscapedToken("foo b\\a\\\"r baz", "taz"),
+              StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
+  EXPECT_THAT(string_util::FindEscapedToken("foo b\\a\\\"r baz", "bazz"),
+              StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
+}
+
+TEST(StringUtilTest, FindEscapedTokenMatchInMiddleToken) {
+  EXPECT_THAT(string_util::FindEscapedToken("babar", "bar"),
+              IsOkAndHolds("bar"));
+}
+
+TEST(StringUtilTest, FindEscapedTokenMatches) {
+  EXPECT_THAT(string_util::FindEscapedToken("foo b\\a\\\"r baz", "ba\"r"),
+              IsOkAndHolds("b\\a\\\"r"));
+  EXPECT_THAT(string_util::FindEscapedToken("\\\\\\\\a", "\\\\a"),
+              IsOkAndHolds("\\\\\\\\a"));
+}
+
+TEST(StringUtilTest, FindEscapedTokenTraversesThroughEscapedText) {
+  std::string_view escaped_text = "bar b\\aar bar\\s bart";
+  ICING_ASSERT_OK_AND_ASSIGN(
+      std::string_view result,
+      string_util::FindEscapedToken(escaped_text, "bar"));
+  // escaped_text = "bar b\\aar bar\\s bart";
+  // escaped_token   ^  ^
+  EXPECT_THAT(result, Eq("bar"));
+
+  // escaped_text = "b\\aar bar\\s bart";
+  // escaped_token          ^  ^
+  const char* result_end = result.data() + result.length();
+  escaped_text = escaped_text.substr(result_end - escaped_text.data());
+  ICING_ASSERT_OK_AND_ASSIGN(
+      result, string_util::FindEscapedToken(escaped_text, "bar"));
+  EXPECT_THAT(result, Eq("bar"));
+
+  // escaped_text = "\\s bart";
+  // escaped_token       ^  ^
+  result_end = result.data() + result.length();
+  escaped_text = escaped_text.substr(result_end - escaped_text.data());
+  ICING_ASSERT_OK_AND_ASSIGN(
+      result, string_util::FindEscapedToken(escaped_text, "bar"));
+  EXPECT_THAT(result, Eq("bar"));
+
+  result_end = result.data() + result.length();
+  escaped_text = escaped_text.substr(result_end - escaped_text.data());
+  EXPECT_THAT(string_util::FindEscapedToken(escaped_text, "bar"),
+              StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
+}
+
+}  // namespace
+
+}  // namespace lib
+}  // namespace icing
\ No newline at end of file
diff --git a/icing/query/query-features.h b/icing/query/query-features.h
index 1471063..9fafba5 100644
--- a/icing/query/query-features.h
+++ b/icing/query/query-features.h
@@ -36,8 +36,14 @@ constexpr Feature kNumericSearchFeature =
 constexpr Feature kVerbatimSearchFeature =
     "VERBATIM_SEARCH";  // Features#VERBATIM_SEARCH
 
-// TODO(b/208654892): Add this as an enabled feature in the query visitor when
-// it gets invoked.
+// This feature covers all additions (other than numeric search and verbatim
+// search) to the query language to bring it into better alignment with the list
+// filters spec.
+// This includes:
+//   - support for function calls
+//   - expanding support for negation and property restriction expressions
+//   - prefix operator '*'
+//   - 'NOT' operator
 constexpr Feature kListFilterQueryLanguageFeature =
     "LIST_FILTER_QUERY_LANGUAGE";  // Features#LIST_FILTER_QUERY_LANGUAGE
 
diff --git a/icing/query/query-processor.cc b/icing/query/query-processor.cc
index 9b03a0e..6760fad 100644
--- a/icing/query/query-processor.cc
+++ b/icing/query/query-processor.cc
@@ -203,8 +203,8 @@ libtextclassifier3::StatusOr<QueryResults> QueryProcessor::ParseAdvancedQuery(
       ranking_strategy == ScoringSpecProto::RankingStrategy::RELEVANCE_SCORE;
   QueryVisitor query_visitor(
       &index_, &numeric_index_, &document_store_, &schema_store_, &normalizer_,
-      plain_tokenizer.get(), std::move(options), search_spec.term_match_type(),
-      needs_term_frequency_info);
+      plain_tokenizer.get(), search_spec.query(), std::move(options),
+      search_spec.term_match_type(), needs_term_frequency_info);
   tree_root->Accept(&query_visitor);
   return std::move(query_visitor).ConsumeResults();
 }
diff --git a/icing/query/suggestion-processor_test.cc b/icing/query/suggestion-processor_test.cc
index e161099..d4ecec0 100644
--- a/icing/query/suggestion-processor_test.cc
+++ b/icing/query/suggestion-processor_test.cc
@@ -14,6 +14,9 @@
 
 #include "icing/query/suggestion-processor.h"
 
+#include <string>
+#include <vector>
+
 #include "gmock/gmock.h"
 #include "icing/document-builder.h"
 #include "icing/index/numeric/dummy-numeric-index.h"
@@ -36,10 +39,19 @@ namespace lib {
 namespace {
 
 using ::testing::IsEmpty;
-using ::testing::SizeIs;
 using ::testing::Test;
 using ::testing::UnorderedElementsAre;
 
+std::vector<std::string> RetrieveSuggestionsText(
+    const std::vector<TermMetadata>& terms) {
+  std::vector<std::string> suggestions;
+  suggestions.reserve(terms.size());
+  for (const TermMetadata& term : terms) {
+    suggestions.push_back(term.content);
+  }
+  return suggestions;
+}
+
 class SuggestionProcessorTest : public Test {
  protected:
   SuggestionProcessorTest()
@@ -181,8 +193,7 @@ TEST_F(SuggestionProcessorTest, MultipleTermsTest_And) {
   ICING_ASSERT_OK_AND_ASSIGN(
       std::vector<TermMetadata> terms,
       suggestion_processor_->QuerySuggestions(suggestion_spec));
-  EXPECT_THAT(terms.at(0).content, "bar foo");
-  EXPECT_THAT(terms, SizeIs(1));
+  EXPECT_THAT(RetrieveSuggestionsText(terms), UnorderedElementsAre("bar foo"));
 }
 
 TEST_F(SuggestionProcessorTest, MultipleTermsTest_AndNary) {
@@ -228,8 +239,8 @@ TEST_F(SuggestionProcessorTest, MultipleTermsTest_AndNary) {
   ICING_ASSERT_OK_AND_ASSIGN(
       std::vector<TermMetadata> terms,
       suggestion_processor_->QuerySuggestions(suggestion_spec));
-  EXPECT_THAT(terms.at(0).content, "bar cat foo");
-  EXPECT_THAT(terms, SizeIs(1));
+  EXPECT_THAT(RetrieveSuggestionsText(terms),
+              UnorderedElementsAre("bar cat foo"));
 }
 
 TEST_F(SuggestionProcessorTest, MultipleTermsTest_Or) {
@@ -277,11 +288,7 @@ TEST_F(SuggestionProcessorTest, MultipleTermsTest_Or) {
   ICING_ASSERT_OK_AND_ASSIGN(
       std::vector<TermMetadata> terms,
       suggestion_processor_->QuerySuggestions(suggestion_spec));
-  std::vector<std::string> suggestions;
-  for (TermMetadata term : terms) {
-    suggestions.push_back(term.content);
-  }
-  EXPECT_THAT(suggestions,
+  EXPECT_THAT(RetrieveSuggestionsText(terms),
               UnorderedElementsAre("bar OR cat fo", "bar OR cat foo"));
 }
 
@@ -340,14 +347,11 @@ TEST_F(SuggestionProcessorTest, MultipleTermsTest_OrNary) {
   ICING_ASSERT_OK_AND_ASSIGN(
       std::vector<TermMetadata> terms,
       suggestion_processor_->QuerySuggestions(suggestion_spec));
-  std::vector<std::string> suggestions;
-  for (TermMetadata term : terms) {
-    suggestions.push_back(term.content);
-  }
   // "fo" in document1, "foo" in document2 and "fool" in document3 could match.
-  EXPECT_THAT(suggestions, UnorderedElementsAre("bar OR cat OR lot fo",
-                                                "bar OR cat OR lot foo",
-                                                "bar OR cat OR lot fool"));
+  EXPECT_THAT(
+      RetrieveSuggestionsText(terms),
+      UnorderedElementsAre("bar OR cat OR lot fo", "bar OR cat OR lot foo",
+                           "bar OR cat OR lot fool"));
 }
 
 TEST_F(SuggestionProcessorTest, MultipleTermsTest_NormalizedTerm) {
@@ -394,22 +398,17 @@ TEST_F(SuggestionProcessorTest, MultipleTermsTest_NormalizedTerm) {
   ICING_ASSERT_OK_AND_ASSIGN(
       std::vector<TermMetadata> terms,
       suggestion_processor_->QuerySuggestions(suggestion_spec));
-  std::vector<std::string> suggestions;
-  for (TermMetadata term : terms) {
-    suggestions.push_back(term.content);
-  }
   // The term is normalized.
-  EXPECT_THAT(suggestions, UnorderedElementsAre("bar foo", "bar fool"));
-  suggestions.clear();
+  EXPECT_THAT(RetrieveSuggestionsText(terms),
+              UnorderedElementsAre("bar foo", "bar fool"));
+
   // Search for "bar AND ḞÖ"
   suggestion_spec.set_prefix("bar ḞÖ");
   ICING_ASSERT_OK_AND_ASSIGN(
       terms, suggestion_processor_->QuerySuggestions(suggestion_spec));
-  for (TermMetadata term : terms) {
-    suggestions.push_back(term.content);
-  }
   // The term is normalized.
-  EXPECT_THAT(suggestions, UnorderedElementsAre("bar foo", "bar fool"));
+  EXPECT_THAT(RetrieveSuggestionsText(terms),
+              UnorderedElementsAre("bar foo", "bar fool"));
 }
 
 TEST_F(SuggestionProcessorTest, NonExistentPrefixTest) {
@@ -441,7 +440,6 @@ TEST_F(SuggestionProcessorTest, NonExistentPrefixTest) {
   ICING_ASSERT_OK_AND_ASSIGN(
       std::vector<TermMetadata> terms,
       suggestion_processor_->QuerySuggestions(suggestion_spec));
-
   EXPECT_THAT(terms, IsEmpty());
 }
 
@@ -474,7 +472,6 @@ TEST_F(SuggestionProcessorTest, PrefixTrailingSpaceTest) {
   ICING_ASSERT_OK_AND_ASSIGN(
       std::vector<TermMetadata> terms,
       suggestion_processor_->QuerySuggestions(suggestion_spec));
-
   EXPECT_THAT(terms, IsEmpty());
 }
 
@@ -506,23 +503,22 @@ TEST_F(SuggestionProcessorTest, NormalizePrefixTest) {
   ICING_ASSERT_OK_AND_ASSIGN(
       std::vector<TermMetadata> terms,
       suggestion_processor_->QuerySuggestions(suggestion_spec));
-  EXPECT_THAT(terms.at(0).content, "foo");
+  EXPECT_THAT(RetrieveSuggestionsText(terms), UnorderedElementsAre("foo"));
 
   suggestion_spec.set_prefix("fO");
   ICING_ASSERT_OK_AND_ASSIGN(
       terms, suggestion_processor_->QuerySuggestions(suggestion_spec));
-  EXPECT_THAT(terms.at(0).content, "foo");
+  EXPECT_THAT(RetrieveSuggestionsText(terms), UnorderedElementsAre("foo"));
 
   suggestion_spec.set_prefix("Fo");
   ICING_ASSERT_OK_AND_ASSIGN(
       terms, suggestion_processor_->QuerySuggestions(suggestion_spec));
-  EXPECT_THAT(terms.at(0).content, "foo");
+  EXPECT_THAT(RetrieveSuggestionsText(terms), UnorderedElementsAre("foo"));
 
   suggestion_spec.set_prefix("FO");
   ICING_ASSERT_OK_AND_ASSIGN(
       terms, suggestion_processor_->QuerySuggestions(suggestion_spec));
-
-  EXPECT_THAT(terms.at(0).content, "foo");
+  EXPECT_THAT(RetrieveSuggestionsText(terms), UnorderedElementsAre("foo"));
 }
 
 TEST_F(SuggestionProcessorTest, ParenthesesOperatorPrefixTest) {
@@ -593,20 +589,34 @@ TEST_F(SuggestionProcessorTest, OtherSpecialPrefixTest) {
   suggestion_spec.mutable_scoring_spec()->set_scoring_match_type(
       TermMatchType::PREFIX);
 
-  ICING_ASSERT_OK_AND_ASSIGN(
-      std::vector<TermMetadata> terms,
-      suggestion_processor_->QuerySuggestions(suggestion_spec));
-  EXPECT_THAT(terms, IsEmpty());
+  auto terms_or = suggestion_processor_->QuerySuggestions(suggestion_spec);
+  if (SearchSpecProto::default_instance().search_type() ==
+      SearchSpecProto::SearchType::ICING_RAW_QUERY) {
+    ICING_ASSERT_OK_AND_ASSIGN(std::vector<TermMetadata> terms, terms_or);
+    EXPECT_THAT(terms, IsEmpty());
+  } else {
+    EXPECT_THAT(terms_or,
+                StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
+  }
 
+  // TODO(b/208654892): Update handling for hyphens to only consider it a hyphen
+  // within a TEXT token (rather than a MINUS token) when surrounded on both
+  // sides by TEXT rather than just preceded by TEXT.
   suggestion_spec.set_prefix("f-");
-  ICING_ASSERT_OK_AND_ASSIGN(
-      terms, suggestion_processor_->QuerySuggestions(suggestion_spec));
+  terms_or = suggestion_processor_->QuerySuggestions(suggestion_spec);
+  ICING_ASSERT_OK_AND_ASSIGN(std::vector<TermMetadata> terms, terms_or);
   EXPECT_THAT(terms, IsEmpty());
 
   suggestion_spec.set_prefix("f OR");
-  ICING_ASSERT_OK_AND_ASSIGN(
-      terms, suggestion_processor_->QuerySuggestions(suggestion_spec));
-  EXPECT_THAT(terms, IsEmpty());
+  terms_or = suggestion_processor_->QuerySuggestions(suggestion_spec);
+  if (SearchSpecProto::default_instance().search_type() ==
+      SearchSpecProto::SearchType::ICING_RAW_QUERY) {
+    ICING_ASSERT_OK_AND_ASSIGN(std::vector<TermMetadata> terms, terms_or);
+    EXPECT_THAT(terms, IsEmpty());
+  } else {
+    EXPECT_THAT(terms_or,
+                StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
+  }
 }
 
 TEST_F(SuggestionProcessorTest, InvalidPrefixTest) {
@@ -635,10 +645,15 @@ TEST_F(SuggestionProcessorTest, InvalidPrefixTest) {
   suggestion_spec.mutable_scoring_spec()->set_scoring_match_type(
       TermMatchType::PREFIX);
 
-  ICING_ASSERT_OK_AND_ASSIGN(
-      std::vector<TermMetadata> terms,
-      suggestion_processor_->QuerySuggestions(suggestion_spec));
-  EXPECT_THAT(terms, IsEmpty());
+  auto terms_or = suggestion_processor_->QuerySuggestions(suggestion_spec);
+  if (SearchSpecProto::default_instance().search_type() ==
+      SearchSpecProto::SearchType::ICING_RAW_QUERY) {
+    ICING_ASSERT_OK_AND_ASSIGN(std::vector<TermMetadata> terms, terms_or);
+    EXPECT_THAT(terms, IsEmpty());
+  } else {
+    EXPECT_THAT(terms_or,
+                StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
+  }
 }
 
 }  // namespace
diff --git a/icing/schema/joinable-property-manager.cc b/icing/schema/joinable-property-manager.cc
index 3977b6b..1606abb 100644
--- a/icing/schema/joinable-property-manager.cc
+++ b/icing/schema/joinable-property-manager.cc
@@ -156,8 +156,7 @@ JoinablePropertyManager::GetJoinablePropertyMetadata(
                         .property_path_to_id_map.find(property_path);
   if (iter == joinable_property_metadata_cache_[schema_type_id]
                   .property_path_to_id_map.end()) {
-    return absl_ports::NotFoundError(
-        "Property path is not joinable or doesn't exist");
+    return nullptr;
   }
 
   JoinablePropertyId joinable_property_id = iter->second;
diff --git a/icing/schema/joinable-property-manager.h b/icing/schema/joinable-property-manager.h
index c7038ce..3ee5963 100644
--- a/icing/schema/joinable-property-manager.h
+++ b/icing/schema/joinable-property-manager.h
@@ -100,9 +100,9 @@ class JoinablePropertyManager {
   //
   // Returns:
   //   - Valid pointer to JoinablePropertyMetadata on success
+  //   - nullptr if property_path doesn't exist (or is not joinable) in the
+  //     joinable metadata list of the schema
   //   - INVALID_ARGUMENT_ERROR if schema type id is invalid
-  //   - NOT_FOUND_ERROR if property_path doesn't exist (or is not joinable) in
-  //     the joinable metadata list of the schema
   libtextclassifier3::StatusOr<const JoinablePropertyMetadata*>
   GetJoinablePropertyMetadata(SchemaTypeId schema_type_id,
                               const std::string& property_path) const;
diff --git a/icing/schema/joinable-property-manager_test.cc b/icing/schema/joinable-property-manager_test.cc
index d9a3841..ceaaa18 100644
--- a/icing/schema/joinable-property-manager_test.cc
+++ b/icing/schema/joinable-property-manager_test.cc
@@ -42,6 +42,7 @@ namespace lib {
 namespace {
 
 using ::testing::ElementsAre;
+using ::testing::IsNull;
 using ::testing::Pointee;
 using ::testing::SizeIs;
 
@@ -491,11 +492,11 @@ TEST_F(JoinablePropertyManagerTest, GetJoinablePropertyMetadataByPathNotExist) {
   EXPECT_THAT(
       schema_type_manager->joinable_property_manager()
           .GetJoinablePropertyMetadata(/*schema_type_id=*/0, "nonExistingPath"),
-      StatusIs(libtextclassifier3::StatusCode::NOT_FOUND));
+      IsOkAndHolds(IsNull()));
   EXPECT_THAT(schema_type_manager->joinable_property_manager()
                   .GetJoinablePropertyMetadata(/*schema_type_id=*/1,
                                                "emails.nonExistingPath"),
-              StatusIs(libtextclassifier3::StatusCode::NOT_FOUND));
+              IsOkAndHolds(IsNull()));
 }
 
 // Note: valid GetMetadataList has been tested in
diff --git a/icing/schema/schema-store.cc b/icing/schema/schema-store.cc
index 0e0c917..065157e 100644
--- a/icing/schema/schema-store.cc
+++ b/icing/schema/schema-store.cc
@@ -369,11 +369,6 @@ SchemaStore::SetSchema(SchemaProto&& new_schema,
                        bool ignore_errors_and_delete_documents) {
   ICING_ASSIGN_OR_RETURN(SchemaUtil::DependentMap new_dependent_map,
                          SchemaUtil::Validate(new_schema));
-  // TODO(b/256022027): validate and extract joinable properties.
-  //   - Joinable config in non-string properties should be ignored, since
-  //     currently we only support string joining.
-  //   - If set joinable, the property itself and all of its nested properties
-  //     should not have REPEATED cardinality.
 
   SetSchemaResult result;
 
diff --git a/icing/schema/schema-store.h b/icing/schema/schema-store.h
index 601d22a..5ad714e 100644
--- a/icing/schema/schema-store.h
+++ b/icing/schema/schema-store.h
@@ -225,10 +225,10 @@ class SchemaStore {
   //
   // Returns:
   //   Valid pointer to JoinablePropertyMetadata on success
+  //   nullptr if property_path doesn't exist (or is not joinable) in the
+  //     joinable metadata list of the schema
   //   FAILED_PRECONDITION if schema hasn't been set yet
   //   INVALID_ARGUMENT if schema type id is invalid
-  //   NOT_FOUND if property_path doesn't exist (or is not joinable) in the
-  //     joinable metadata list of the schema
   libtextclassifier3::StatusOr<const JoinablePropertyMetadata*>
   GetJoinablePropertyMetadata(SchemaTypeId schema_type_id,
                               const std::string& property_path) const;
diff --git a/icing/schema/schema-util.cc b/icing/schema/schema-util.cc
index 0589ada..ea0d85a 100644
--- a/icing/schema/schema-util.cc
+++ b/icing/schema/schema-util.cc
@@ -15,6 +15,7 @@
 #include "icing/schema/schema-util.h"
 
 #include <cstdint>
+#include <queue>
 #include <string>
 #include <string_view>
 #include <unordered_map>
@@ -143,7 +144,7 @@ void AddIncompatibleChangeToDelta(
   auto dependent_types_itr =
       new_schema_dependent_map.find(old_type_config.schema_type());
   if (dependent_types_itr != new_schema_dependent_map.end()) {
-    for (std::string_view dependent_type : dependent_types_itr->second) {
+    for (const auto& [dependent_type, _] : dependent_types_itr->second) {
       // The types from new_schema that depend on the current
       // old_type_config may not present in old_schema.
       // Those types will be listed at schema_delta.schema_types_new
@@ -176,14 +177,15 @@ libtextclassifier3::Status ExpandTranstiveDependents(
     return libtextclassifier3::Status::OK;
   }
   pending_expansions->insert(type);
-  std::unordered_set<std::string_view> expanded_dependents;
+  std::unordered_map<std::string_view, std::vector<const PropertyConfigProto*>>
+      expanded_dependents;
 
   // Add all of the direct dependents.
   expanded_dependents.reserve(itr->second.size());
   expanded_dependents.insert(itr->second.begin(), itr->second.end());
 
   // Iterate through each direct dependent and add their indirect dependents.
-  for (std::string_view dep : itr->second) {
+  for (const auto& [dep, _] : itr->second) {
     // 1. Check if we're in the middle of expanding this type - IOW there's a
     // cycle!
     if (pending_expansions->count(dep) > 0) {
@@ -206,8 +208,12 @@ libtextclassifier3::Status ExpandTranstiveDependents(
     auto dep_expanded_itr = expanded_dependent_map->find(dep);
     expanded_dependents.reserve(expanded_dependents.size() +
                                 dep_expanded_itr->second.size());
-    expanded_dependents.insert(dep_expanded_itr->second.begin(),
-                               dep_expanded_itr->second.end());
+    for (const auto& [dep_dependent, _] : dep_expanded_itr->second) {
+      // Insert a transitive dependent `dep_dependent` for `type`. Also since
+      // there is no direct edge between `type` and `dep_dependent`, the direct
+      // edge (i.e. PropertyConfigProto*) vector is empty.
+      expanded_dependents.insert({dep_dependent, {}});
+    }
   }
   expanded_dependent_map->insert({type, std::move(expanded_dependents)});
   pending_expansions->erase(type);
@@ -283,7 +289,8 @@ BuildTransitiveDependentGraph(const SchemaProto& schema) {
         if (known_types.count(property_schema_type) == 0) {
           unknown_types.insert(property_schema_type);
         }
-        dependent_map[property_schema_type].insert(schema_type);
+        dependent_map[property_schema_type][schema_type].push_back(
+            &property_config);
       }
     }
   }
@@ -305,6 +312,9 @@ libtextclassifier3::StatusOr<SchemaUtil::DependentMap> SchemaUtil::Validate(
   // already.
   std::unordered_set<std::string_view> known_property_names;
 
+  // Tracks PropertyConfigs containing joinable properties.
+  std::unordered_set<std::string_view> schema_types_with_joinable_property;
+
   // 2. Validate the properties of each type.
   for (const auto& type_config : schema.types()) {
     std::string_view schema_type(type_config.schema_type());
@@ -351,6 +361,55 @@ libtextclassifier3::StatusOr<SchemaUtil::DependentMap> SchemaUtil::Validate(
             property_config.string_indexing_config(), data_type, schema_type,
             property_name));
       }
+
+      ICING_RETURN_IF_ERROR(ValidateJoinableConfig(
+          property_config.joinable_config(), data_type,
+          property_config.cardinality(), schema_type, property_name));
+      if (property_config.joinable_config().value_type() !=
+          JoinableConfig::ValueType::NONE) {
+        schema_types_with_joinable_property.insert(schema_type);
+      }
+    }
+  }
+
+  // BFS traverse the dependent graph to make sure that no nested levels
+  // (properties with DOCUMENT data type) have REPEATED cardinality while
+  // depending on schema types with joinable property.
+  std::queue<std::string_view> frontier;
+  for (const auto& schema_type : schema_types_with_joinable_property) {
+    frontier.push(schema_type);
+  }
+  std::unordered_set<std::string_view> traversed =
+      std::move(schema_types_with_joinable_property);
+  while (!frontier.empty()) {
+    std::string_view schema_type = frontier.front();
+    frontier.pop();
+
+    const auto it = dependent_map.find(schema_type);
+    if (it == dependent_map.end()) {
+      continue;
+    }
+
+    // Check every type that has a property of type schema_type.
+    for (const auto& [next_schema_type, property_configs] : it->second) {
+      // Check all properties in "next_schema_type" that are of type
+      // "schema_type".
+      for (const PropertyConfigProto* property_config : property_configs) {
+        if (property_config != nullptr &&
+            property_config->cardinality() ==
+                PropertyConfigProto::Cardinality::REPEATED) {
+          return absl_ports::InvalidArgumentError(absl_ports::StrCat(
+              "Schema type '", next_schema_type,
+              "' cannot have REPEATED nested document property '",
+              property_config->property_name(),
+              "' while connecting to some joinable properties"));
+        }
+      }
+
+      if (traversed.count(next_schema_type) == 0) {
+        traversed.insert(next_schema_type);
+        frontier.push(next_schema_type);
+      }
     }
   }
 
@@ -440,6 +499,35 @@ libtextclassifier3::Status SchemaUtil::ValidateStringIndexingConfig(
   return libtextclassifier3::Status::OK;
 }
 
+libtextclassifier3::Status SchemaUtil::ValidateJoinableConfig(
+    const JoinableConfig& config, PropertyConfigProto::DataType::Code data_type,
+    PropertyConfigProto::Cardinality::Code cardinality,
+    std::string_view schema_type, std::string_view property_name) {
+  if (config.value_type() == JoinableConfig::ValueType::QUALIFIED_ID) {
+    if (data_type != PropertyConfigProto::DataType::STRING) {
+      return absl_ports::InvalidArgumentError(
+          absl_ports::StrCat("Qualified id joinable property '", property_name,
+                             "' is required to have STRING data type"));
+    }
+
+    if (cardinality == PropertyConfigProto::Cardinality::REPEATED) {
+      return absl_ports::InvalidArgumentError(
+          absl_ports::StrCat("Qualified id joinable property '", property_name,
+                             "' cannot have REPEATED cardinality"));
+    }
+  }
+
+  if (config.propagate_delete() &&
+      config.value_type() != JoinableConfig::ValueType::QUALIFIED_ID) {
+    return absl_ports::InvalidArgumentError(
+        absl_ports::StrCat("Field 'property_name' '", property_name,
+                           "' is required to have QUALIFIED_ID joinable "
+                           "value type with delete propagation enabled"));
+  }
+
+  return libtextclassifier3::Status::OK;
+}
+
 void SchemaUtil::BuildTypeConfigMap(
     const SchemaProto& schema, SchemaUtil::TypeConfigMap* type_config_map) {
   type_config_map->clear();
diff --git a/icing/schema/schema-util.h b/icing/schema/schema-util.h
index e5747bb..47bb76b 100644
--- a/icing/schema/schema-util.h
+++ b/icing/schema/schema-util.h
@@ -34,9 +34,19 @@ class SchemaUtil {
       std::unordered_map<std::string, const SchemaTypeConfigProto>;
 
   // If A -> B is indicated in the map, then type A must be built before
-  // building type B, i.e. B depends on A.
-  using DependentMap = std::unordered_map<std::string_view,
-                                          std::unordered_set<std::string_view>>;
+  // building type B, i.e. B has a property of type A. Also include all
+  // PropertyConfigProto (with DOCUMENT data_type) pointers which directly
+  // connects type A and B. IOW, this vector of PropertyConfigProto* are "direct
+  // edges" connecting A and B directly. It will be an empty vector if A and B
+  // are not "directly" connected, but instead via another intermediate level of
+  // schema type. For example, the actual dependency is A -> C -> B, so there
+  // will be A -> C and C -> B with valid PropertyConfigProto* respectively in
+  // this map, but we will also expand transitive dependents: add A -> B into
+  // dependent map with empty vector of "edges".
+  using DependentMap = std::unordered_map<
+      std::string_view,
+      std::unordered_map<std::string_view,
+                         std::vector<const PropertyConfigProto*>>>;
 
   struct SchemaDelta {
     // Which schema types were present in the old schema, but were deleted from
@@ -113,6 +123,11 @@ class SchemaUtil {
   //      itself, thus creating an infinite loop.
   //  13. Two SchemaTypeConfigProtos cannot have properties that reference each
   //      other's schema_type, thus creating an infinite loop.
+  //  14. PropertyConfigProtos.joinable_config must be valid. See
+  //      ValidateJoinableConfig for more details.
+  //  15. Any PropertyConfigProtos with nested DOCUMENT data type must not have
+  //      REPEATED cardinality if they reference a schema type containing
+  //      joinable property.
   //
   //  TODO(b/171996137): Clarify 12 and 13 are only for indexed properties, once
   //  document properties can be opted out of indexing.
@@ -121,7 +136,7 @@ class SchemaUtil {
   //   On success, a dependent map from each types to their dependent types
   //   that depend on it directly or indirectly.
   //   ALREADY_EXISTS for case 1 and 2
-  //   INVALID_ARGUMENT for 3-13
+  //   INVALID_ARGUMENT for 3-15
   static libtextclassifier3::StatusOr<DependentMap> Validate(
       const SchemaProto& schema);
 
@@ -145,6 +160,8 @@ class SchemaUtil {
   //      `SchemaDelta.schema_types_deleted`
   //   3. A schema type's new definition would mean any existing data of the old
   //      definition is now incompatible.
+  //   4. The derived join index would be incompatible. This is held in
+  //      `SchemaDelta.join_incompatible`.
   //
   // For case 1, the two schemas would result in an incompatible index if:
   //   1.1. The new SchemaProto has a different set of indexed properties than
@@ -167,6 +184,11 @@ class SchemaUtil {
   //        scale defined as:
   //          LEAST <REPEATED - OPTIONAL - REQUIRED> MOST
   //
+  // For case 4, the two schemas would result in an incompatible join if:
+  //   4.1. A SchematypeConfig exists in the new SchemaProto that has a
+  //        different set of joinable properties than it did in the old
+  //        SchemaProto.
+  //
   // A property is defined by the combination of the
   // SchemaTypeConfig.schema_type and the PropertyConfigProto.property_name.
   //
@@ -227,6 +249,22 @@ class SchemaUtil {
       const StringIndexingConfig& config,
       PropertyConfigProto::DataType::Code data_type,
       std::string_view schema_type, std::string_view property_name);
+
+  // Checks that the 'joinable_config' satisfies the following rules:
+  //   1. If the data type matches joinable value type
+  //      a. Only STRING data types can use QUALIFIED_ID joinable value type
+  //   2. Only QUALIFIED_ID joinable value type can have delete propagation
+  //      enabled
+  //   3. Any joinable property should have non-REPEATED cardinality
+  //
+  // Returns:
+  //   INVALID_ARGUMENT if any of the rules are not followed
+  //   OK on success
+  static libtextclassifier3::Status ValidateJoinableConfig(
+      const JoinableConfig& config,
+      PropertyConfigProto::DataType::Code data_type,
+      PropertyConfigProto::Cardinality::Code cardinality,
+      std::string_view schema_type, std::string_view property_name);
 };
 
 }  // namespace lib
diff --git a/icing/schema/schema-util_test.cc b/icing/schema/schema-util_test.cc
index 44d8def..2d1e683 100644
--- a/icing/schema/schema-util_test.cc
+++ b/icing/schema/schema-util_test.cc
@@ -30,9 +30,13 @@ namespace icing {
 namespace lib {
 namespace {
 
+using portable_equals_proto::EqualsProto;
 using ::testing::Eq;
 using ::testing::HasSubstr;
 using ::testing::IsEmpty;
+using ::testing::Pair;
+using ::testing::Pointee;
+using ::testing::UnorderedElementsAre;
 
 // Properties/fields in a schema type
 constexpr char kEmailType[] = "EmailMessage";
@@ -118,12 +122,32 @@ TEST(SchemaUtilTest, DependentGraphAlphabeticalOrder) {
   ICING_ASSERT_OK_AND_ASSIGN(SchemaUtil::DependentMap d_map,
                              SchemaUtil::Validate(schema));
   EXPECT_THAT(d_map, testing::SizeIs(5));
-  EXPECT_THAT(d_map["F"],
-              testing::UnorderedElementsAre("A", "B", "C", "D", "E"));
-  EXPECT_THAT(d_map["E"], testing::UnorderedElementsAre("A", "B", "C", "D"));
-  EXPECT_THAT(d_map["D"], testing::UnorderedElementsAre("A", "B"));
-  EXPECT_THAT(d_map["C"], testing::UnorderedElementsAre("A", "B"));
-  EXPECT_THAT(d_map["B"], testing::UnorderedElementsAre("A"));
+  EXPECT_THAT(
+      d_map["F"],
+      UnorderedElementsAre(Pair("A", IsEmpty()), Pair("B", IsEmpty()),
+                           Pair("C", IsEmpty()), Pair("D", IsEmpty()),
+                           Pair("E", UnorderedElementsAre(Pointee(
+                                         EqualsProto(type_e.properties(0)))))));
+  EXPECT_THAT(d_map["E"],
+              UnorderedElementsAre(
+                  Pair("A", IsEmpty()), Pair("B", IsEmpty()),
+                  Pair("C", UnorderedElementsAre(
+                                Pointee(EqualsProto(type_c.properties(0))))),
+                  Pair("D", UnorderedElementsAre(
+                                Pointee(EqualsProto(type_d.properties(0)))))));
+  EXPECT_THAT(
+      d_map["D"],
+      UnorderedElementsAre(Pair("A", IsEmpty()),
+                           Pair("B", UnorderedElementsAre(Pointee(
+                                         EqualsProto(type_b.properties(1)))))));
+  EXPECT_THAT(
+      d_map["C"],
+      UnorderedElementsAre(Pair("A", IsEmpty()),
+                           Pair("B", UnorderedElementsAre(Pointee(
+                                         EqualsProto(type_b.properties(0)))))));
+  EXPECT_THAT(d_map["B"], UnorderedElementsAre(Pair(
+                              "A", UnorderedElementsAre(Pointee(
+                                       EqualsProto(type_a.properties(0)))))));
 }
 
 TEST(SchemaUtilTest, DependentGraphReverseAlphabeticalOrder) {
@@ -206,12 +230,32 @@ TEST(SchemaUtilTest, DependentGraphReverseAlphabeticalOrder) {
   ICING_ASSERT_OK_AND_ASSIGN(SchemaUtil::DependentMap d_map,
                              SchemaUtil::Validate(schema));
   EXPECT_THAT(d_map, testing::SizeIs(5));
-  EXPECT_THAT(d_map["F"],
-              testing::UnorderedElementsAre("A", "B", "C", "D", "E"));
-  EXPECT_THAT(d_map["E"], testing::UnorderedElementsAre("A", "B", "C", "D"));
-  EXPECT_THAT(d_map["D"], testing::UnorderedElementsAre("A", "B"));
-  EXPECT_THAT(d_map["C"], testing::UnorderedElementsAre("A", "B"));
-  EXPECT_THAT(d_map["B"], testing::UnorderedElementsAre("A"));
+  EXPECT_THAT(
+      d_map["F"],
+      UnorderedElementsAre(Pair("A", IsEmpty()), Pair("B", IsEmpty()),
+                           Pair("C", IsEmpty()), Pair("D", IsEmpty()),
+                           Pair("E", UnorderedElementsAre(Pointee(
+                                         EqualsProto(type_e.properties(0)))))));
+  EXPECT_THAT(d_map["E"],
+              UnorderedElementsAre(
+                  Pair("A", IsEmpty()), Pair("B", IsEmpty()),
+                  Pair("C", UnorderedElementsAre(
+                                Pointee(EqualsProto(type_c.properties(0))))),
+                  Pair("D", UnorderedElementsAre(
+                                Pointee(EqualsProto(type_d.properties(0)))))));
+  EXPECT_THAT(
+      d_map["D"],
+      UnorderedElementsAre(Pair("A", IsEmpty()),
+                           Pair("B", UnorderedElementsAre(Pointee(
+                                         EqualsProto(type_b.properties(1)))))));
+  EXPECT_THAT(
+      d_map["C"],
+      UnorderedElementsAre(Pair("A", IsEmpty()),
+                           Pair("B", UnorderedElementsAre(Pointee(
+                                         EqualsProto(type_b.properties(0)))))));
+  EXPECT_THAT(d_map["B"], UnorderedElementsAre(Pair(
+                              "A", UnorderedElementsAre(Pointee(
+                                       EqualsProto(type_a.properties(0)))))));
 }
 
 TEST(SchemaUtilTest, DependentGraphMixedOrder) {
@@ -293,12 +337,32 @@ TEST(SchemaUtilTest, DependentGraphMixedOrder) {
   ICING_ASSERT_OK_AND_ASSIGN(SchemaUtil::DependentMap d_map,
                              SchemaUtil::Validate(schema));
   EXPECT_THAT(d_map, testing::SizeIs(5));
-  EXPECT_THAT(d_map["F"],
-              testing::UnorderedElementsAre("A", "B", "C", "D", "E"));
-  EXPECT_THAT(d_map["E"], testing::UnorderedElementsAre("A", "B", "C", "D"));
-  EXPECT_THAT(d_map["D"], testing::UnorderedElementsAre("A", "B"));
-  EXPECT_THAT(d_map["C"], testing::UnorderedElementsAre("A", "B"));
-  EXPECT_THAT(d_map["B"], testing::UnorderedElementsAre("A"));
+  EXPECT_THAT(
+      d_map["F"],
+      UnorderedElementsAre(Pair("A", IsEmpty()), Pair("B", IsEmpty()),
+                           Pair("C", IsEmpty()), Pair("D", IsEmpty()),
+                           Pair("E", UnorderedElementsAre(Pointee(
+                                         EqualsProto(type_e.properties(0)))))));
+  EXPECT_THAT(d_map["E"],
+              UnorderedElementsAre(
+                  Pair("A", IsEmpty()), Pair("B", IsEmpty()),
+                  Pair("C", UnorderedElementsAre(
+                                Pointee(EqualsProto(type_c.properties(0))))),
+                  Pair("D", UnorderedElementsAre(
+                                Pointee(EqualsProto(type_d.properties(0)))))));
+  EXPECT_THAT(
+      d_map["D"],
+      UnorderedElementsAre(Pair("A", IsEmpty()),
+                           Pair("B", UnorderedElementsAre(Pointee(
+                                         EqualsProto(type_b.properties(1)))))));
+  EXPECT_THAT(
+      d_map["C"],
+      UnorderedElementsAre(Pair("A", IsEmpty()),
+                           Pair("B", UnorderedElementsAre(Pointee(
+                                         EqualsProto(type_b.properties(0)))))));
+  EXPECT_THAT(d_map["B"], UnorderedElementsAre(Pair(
+                              "A", UnorderedElementsAre(Pointee(
+                                       EqualsProto(type_a.properties(0)))))));
 }
 
 TEST(SchemaUtilTest, TopLevelCycle) {
@@ -888,7 +952,8 @@ TEST(SchemaUtilTest, DifferentSchemaTypeIsIncompatible) {
   SchemaUtil::SchemaDelta schema_delta;
   schema_delta.schema_types_incompatible.emplace(kEmailType);
   // kEmailType depends on kMessageType
-  SchemaUtil::DependentMap dependents_map = {{kMessageType, {kEmailType}}};
+  SchemaUtil::DependentMap dependents_map = {
+      {kMessageType, {{kEmailType, {}}}}};
   SchemaUtil::SchemaDelta actual = SchemaUtil::ComputeCompatibilityDelta(
       old_schema, new_schema, dependents_map);
   EXPECT_THAT(actual, Eq(schema_delta));
@@ -1403,7 +1468,7 @@ TEST(SchemaUtilTest, IndexNestedDocumentsIndexIncompatible) {
   // unaffected.
   SchemaUtil::SchemaDelta schema_delta;
   schema_delta.schema_types_index_incompatible.emplace(kPersonType);
-  SchemaUtil::DependentMap dependents_map = {{kEmailType, {kPersonType}}};
+  SchemaUtil::DependentMap dependents_map = {{kEmailType, {{kPersonType, {}}}}};
   SchemaUtil::SchemaDelta actual = SchemaUtil::ComputeCompatibilityDelta(
       no_nested_index_schema, nested_index_schema, dependents_map);
   EXPECT_THAT(actual, Eq(schema_delta));
@@ -1466,6 +1531,547 @@ TEST(SchemaUtilTest, ValidateStringIndexingConfigShouldHaveTokenizer) {
   EXPECT_THAT(SchemaUtil::Validate(schema), IsOk());
 }
 
+TEST(SchemaUtilTest,
+     ValidateJoinablePropertyTypeQualifiedIdShouldHaveStringDataType) {
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("MyType").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("Foo")
+                  .SetDataType(TYPE_INT64)
+                  .SetJoinable(JOINABLE_VALUE_TYPE_QUALIFIED_ID,
+                               /*propagate_delete=*/false)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
+  // Error if data type is not STRING for qualified id joinable value type.
+  EXPECT_THAT(SchemaUtil::Validate(schema),
+              StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
+
+  // Passes once we set STRING as the data type.
+  schema = SchemaBuilder()
+               .AddType(SchemaTypeConfigBuilder().SetType("MyType").AddProperty(
+                   PropertyConfigBuilder()
+                       .SetName("Foo")
+                       .SetDataType(TYPE_STRING)
+                       .SetJoinable(JOINABLE_VALUE_TYPE_QUALIFIED_ID,
+                                    /*propagate_delete=*/false)
+                       .SetCardinality(CARDINALITY_REQUIRED)))
+               .Build();
+  EXPECT_THAT(SchemaUtil::Validate(schema), IsOk());
+}
+
+TEST(SchemaUtilTest, ValidateJoinablePropertyShouldNotHaveRepeatedCardinality) {
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("MyType").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("Foo")
+                  .SetDataType(TYPE_STRING)
+                  .SetJoinable(JOINABLE_VALUE_TYPE_QUALIFIED_ID,
+                               /*propagate_delete=*/false)
+                  .SetCardinality(CARDINALITY_REPEATED)))
+          .Build();
+
+  // Error if using REPEATED cardinality for joinable property.
+  EXPECT_THAT(SchemaUtil::Validate(schema),
+              StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
+
+  // Passes once we use OPTIONAL cardinality with joinable property.
+  schema = SchemaBuilder()
+               .AddType(SchemaTypeConfigBuilder().SetType("MyType").AddProperty(
+                   PropertyConfigBuilder()
+                       .SetName("Foo")
+                       .SetDataType(TYPE_STRING)
+                       .SetJoinable(JOINABLE_VALUE_TYPE_QUALIFIED_ID,
+                                    /*propagate_delete=*/false)
+                       .SetCardinality(CARDINALITY_OPTIONAL)))
+               .Build();
+  EXPECT_THAT(SchemaUtil::Validate(schema), IsOk());
+
+  // Passes once we use REQUIRED cardinality with joinable property.
+  schema = SchemaBuilder()
+               .AddType(SchemaTypeConfigBuilder().SetType("MyType").AddProperty(
+                   PropertyConfigBuilder()
+                       .SetName("Foo")
+                       .SetDataType(TYPE_STRING)
+                       .SetJoinable(JOINABLE_VALUE_TYPE_QUALIFIED_ID,
+                                    /*propagate_delete=*/false)
+                       .SetCardinality(CARDINALITY_REQUIRED)))
+               .Build();
+  EXPECT_THAT(SchemaUtil::Validate(schema), IsOk());
+
+  // Passes once we use REPEATED cardinality with non-joinable property.
+  schema = SchemaBuilder()
+               .AddType(SchemaTypeConfigBuilder().SetType("MyType").AddProperty(
+                   PropertyConfigBuilder()
+                       .SetName("Foo")
+                       .SetDataType(TYPE_STRING)
+                       .SetJoinable(JOINABLE_VALUE_TYPE_NONE,
+                                    /*propagate_delete=*/false)
+                       .SetCardinality(CARDINALITY_REPEATED)))
+               .Build();
+  EXPECT_THAT(SchemaUtil::Validate(schema), IsOk());
+}
+
+TEST(SchemaUtilTest,
+     ValidateJoinablePropertyWithDeletePropagationShouldHaveTypeQualifiedId) {
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("MyType").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("Foo")
+                  .SetDataType(TYPE_STRING)
+                  .SetJoinable(JOINABLE_VALUE_TYPE_NONE,
+                               /*propagate_delete=*/true)
+                  .SetCardinality(CARDINALITY_REQUIRED)))
+          .Build();
+
+  // Error if enabling delete propagation with non qualified id joinable value
+  // type.
+  EXPECT_THAT(SchemaUtil::Validate(schema),
+              StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
+
+  // Passes once we set qualified id joinable value type with delete propagation
+  // enabled.
+  schema = SchemaBuilder()
+               .AddType(SchemaTypeConfigBuilder().SetType("MyType").AddProperty(
+                   PropertyConfigBuilder()
+                       .SetName("Foo")
+                       .SetDataType(TYPE_STRING)
+                       .SetJoinable(JOINABLE_VALUE_TYPE_QUALIFIED_ID,
+                                    /*propagate_delete=*/true)
+                       .SetCardinality(CARDINALITY_REQUIRED)))
+               .Build();
+  EXPECT_THAT(SchemaUtil::Validate(schema), IsOk());
+
+  // Passes once we disable delete propagation.
+  schema = SchemaBuilder()
+               .AddType(SchemaTypeConfigBuilder().SetType("MyType").AddProperty(
+                   PropertyConfigBuilder()
+                       .SetName("Foo")
+                       .SetDataType(TYPE_STRING)
+                       .SetJoinable(JOINABLE_VALUE_TYPE_NONE,
+                                    /*propagate_delete=*/false)
+                       .SetCardinality(CARDINALITY_REQUIRED)))
+               .Build();
+  EXPECT_THAT(SchemaUtil::Validate(schema), IsOk());
+}
+
+TEST(SchemaUtilTest,
+     ValidateNestedJoinablePropertyShouldNotHaveNestedRepeatedCardinality) {
+  // Dependency and nested document property cardinality:
+  //   "C" --(REPEATED)--> "B" --(OPTIONAL)--> "A"
+  // where "A" contains joinable property. This should not be allowed.
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("A").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("Foo")
+                  .SetDataType(TYPE_STRING)
+                  .SetJoinable(JOINABLE_VALUE_TYPE_QUALIFIED_ID,
+                               /*propagate_delete=*/false)
+                  .SetCardinality(CARDINALITY_OPTIONAL)))
+          .AddType(SchemaTypeConfigBuilder().SetType("B").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("a")
+                  .SetDataTypeDocument("A",
+                                       /*index_nested_properties=*/false)
+                  .SetCardinality(CARDINALITY_OPTIONAL)))
+          .AddType(SchemaTypeConfigBuilder().SetType("C").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("b")
+                  .SetDataTypeDocument("B",
+                                       /*index_nested_properties=*/false)
+                  .SetCardinality(CARDINALITY_REPEATED)))
+          .Build();
+  EXPECT_THAT(SchemaUtil::Validate(schema),
+              StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
+
+  // Passes once we use non-REPEATED cardinality for "C.b", i.e. the dependency
+  // and nested document property cardinality becomes:
+  //   "C" --(OPTIONAL)--> "B" --(OPTIONAL)--> "A"
+  schema = SchemaBuilder()
+               .AddType(SchemaTypeConfigBuilder().SetType("A").AddProperty(
+                   PropertyConfigBuilder()
+                       .SetName("Foo")
+                       .SetDataType(TYPE_STRING)
+                       .SetJoinable(JOINABLE_VALUE_TYPE_QUALIFIED_ID,
+                                    /*propagate_delete=*/false)
+                       .SetCardinality(CARDINALITY_OPTIONAL)))
+               .AddType(SchemaTypeConfigBuilder().SetType("B").AddProperty(
+                   PropertyConfigBuilder()
+                       .SetName("a")
+                       .SetDataTypeDocument("A",
+                                            /*index_nested_properties=*/false)
+                       .SetCardinality(CARDINALITY_OPTIONAL)))
+               .AddType(SchemaTypeConfigBuilder().SetType("C").AddProperty(
+                   PropertyConfigBuilder()
+                       .SetName("b")
+                       .SetDataTypeDocument("B",
+                                            /*index_nested_properties=*/false)
+                       .SetCardinality(CARDINALITY_OPTIONAL)))
+               .Build();
+  EXPECT_THAT(SchemaUtil::Validate(schema), IsOk());
+}
+
+TEST(
+    SchemaUtilTest,
+    ValidateNestedJoinablePropertyShouldAllowRepeatedCardinalityIfNoJoinableProperty) {
+  // Dependency and nested document property cardinality:
+  //   "C" --(OPTIONAL)--> "B" --(REPEATED)--> "A"
+  // where only "B" contains joinable property. This should be allowed.
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("A").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("Foo")
+                  .SetDataType(TYPE_STRING)
+                  .SetJoinable(JOINABLE_VALUE_TYPE_NONE,
+                               /*propagate_delete=*/false)
+                  .SetCardinality(CARDINALITY_OPTIONAL)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("B")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("a")
+                                        .SetDataTypeDocument(
+                                            "A",
+                                            /*index_nested_properties=*/false)
+                                        .SetCardinality(CARDINALITY_REPEATED))
+                       .AddProperty(
+                           PropertyConfigBuilder()
+                               .SetName("Bar")
+                               .SetDataType(TYPE_STRING)
+                               .SetJoinable(JOINABLE_VALUE_TYPE_QUALIFIED_ID,
+                                            /*propagate_delete=*/false)
+                               .SetCardinality(CARDINALITY_OPTIONAL)))
+          .AddType(SchemaTypeConfigBuilder().SetType("C").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("b")
+                  .SetDataTypeDocument("B",
+                                       /*index_nested_properties=*/false)
+                  .SetCardinality(CARDINALITY_OPTIONAL)))
+          .Build();
+
+  // Passes since nested schema type with REPEATED cardinality doesn't have
+  // joinable property.
+  EXPECT_THAT(SchemaUtil::Validate(schema), IsOk());
+}
+
+TEST(SchemaUtilTest,
+     ValidateNestedJoinablePropertyMultiplePropertiesWithSameSchema) {
+  // Dependency and nested document property cardinality:
+  //        --(a1: OPTIONAL)--
+  //      /                    \
+  // B --                        --> A
+  //      \                    /
+  //        --(a2: REPEATED)--
+  // where "A" contains joinable property. This should not be allowed.
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("A").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("Foo")
+                  .SetDataType(TYPE_STRING)
+                  .SetJoinable(JOINABLE_VALUE_TYPE_QUALIFIED_ID,
+                               /*propagate_delete=*/false)
+                  .SetCardinality(CARDINALITY_OPTIONAL)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("B")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("a1")
+                                        .SetDataTypeDocument(
+                                            "A",
+                                            /*index_nested_properties=*/false)
+                                        .SetCardinality(CARDINALITY_OPTIONAL))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("a2")
+                                        .SetDataTypeDocument(
+                                            "A",
+                                            /*index_nested_properties=*/false)
+                                        .SetCardinality(CARDINALITY_REPEATED)))
+          .Build();
+  EXPECT_THAT(SchemaUtil::Validate(schema),
+              StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
+
+  // Passes once we use non-REPEATED cardinality for "B.a2", i.e. the dependency
+  // and nested document property cardinality becomes:
+  //        --(a1: OPTIONAL)--
+  //      /                    \
+  // B --                        --> A
+  //      \                    /
+  //        --(a2: OPTIONAL)--
+  schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("A").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("Foo")
+                  .SetDataType(TYPE_STRING)
+                  .SetJoinable(JOINABLE_VALUE_TYPE_QUALIFIED_ID,
+                               /*propagate_delete=*/false)
+                  .SetCardinality(CARDINALITY_OPTIONAL)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("B")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("a1")
+                                        .SetDataTypeDocument(
+                                            "A",
+                                            /*index_nested_properties=*/false)
+                                        .SetCardinality(CARDINALITY_OPTIONAL))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("a2")
+                                        .SetDataTypeDocument(
+                                            "A",
+                                            /*index_nested_properties=*/false)
+                                        .SetCardinality(CARDINALITY_OPTIONAL)))
+          .Build();
+  EXPECT_THAT(SchemaUtil::Validate(schema), IsOk());
+}
+
+TEST(SchemaUtilTest, ValidateNestedJoinablePropertyDiamondRelationship) {
+  // Dependency and nested document property cardinality:
+  //           B
+  //         /   \
+  // (OPTIONAL) (OPTIONAL)
+  //       /       \
+  // D ---           --> A
+  //       \       /
+  // (OPTIONAL) (OPTIONAL)
+  //         \   /
+  //           C
+  // where "A" contains joinable property. This should be allowed.
+  SchemaProto schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("A").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("Foo")
+                  .SetDataType(TYPE_STRING)
+                  .SetJoinable(JOINABLE_VALUE_TYPE_QUALIFIED_ID,
+                               /*propagate_delete=*/false)
+                  .SetCardinality(CARDINALITY_OPTIONAL)))
+          .AddType(SchemaTypeConfigBuilder().SetType("B").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("a")
+                  .SetDataTypeDocument("A",
+                                       /*index_nested_properties=*/false)
+                  .SetCardinality(CARDINALITY_OPTIONAL)))
+          .AddType(SchemaTypeConfigBuilder().SetType("C").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("a")
+                  .SetDataTypeDocument("A",
+                                       /*index_nested_properties=*/false)
+                  .SetCardinality(CARDINALITY_OPTIONAL)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("D")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("b")
+                                        .SetDataTypeDocument(
+                                            "B",
+                                            /*index_nested_properties=*/false)
+                                        .SetCardinality(CARDINALITY_OPTIONAL))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("c")
+                                        .SetDataTypeDocument(
+                                            "C",
+                                            /*index_nested_properties=*/false)
+                                        .SetCardinality(CARDINALITY_OPTIONAL)))
+          .Build();
+  EXPECT_THAT(SchemaUtil::Validate(schema), IsOk());
+
+  // Fails once we change any of edge to REPEATED cardinality.
+  //           B
+  //         /   \
+  // (REPEATED) (OPTIONAL)
+  //       /       \
+  // D ---           --> A
+  //       \       /
+  // (OPTIONAL) (OPTIONAL)
+  //         \   /
+  //           C
+  schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("A").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("Foo")
+                  .SetDataType(TYPE_STRING)
+                  .SetJoinable(JOINABLE_VALUE_TYPE_QUALIFIED_ID,
+                               /*propagate_delete=*/false)
+                  .SetCardinality(CARDINALITY_OPTIONAL)))
+          .AddType(SchemaTypeConfigBuilder().SetType("B").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("a")
+                  .SetDataTypeDocument("A",
+                                       /*index_nested_properties=*/false)
+                  .SetCardinality(CARDINALITY_OPTIONAL)))
+          .AddType(SchemaTypeConfigBuilder().SetType("C").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("a")
+                  .SetDataTypeDocument("A",
+                                       /*index_nested_properties=*/false)
+                  .SetCardinality(CARDINALITY_OPTIONAL)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("D")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("b")
+                                        .SetDataTypeDocument(
+                                            "B",
+                                            /*index_nested_properties=*/false)
+                                        .SetCardinality(CARDINALITY_REPEATED))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("c")
+                                        .SetDataTypeDocument(
+                                            "C",
+                                            /*index_nested_properties=*/false)
+                                        .SetCardinality(CARDINALITY_OPTIONAL)))
+          .Build();
+  EXPECT_THAT(SchemaUtil::Validate(schema),
+              StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
+
+  //           B
+  //         /   \
+  // (OPTIONAL) (REPEATED)
+  //       /       \
+  // D ---           --> A
+  //       \       /
+  // (OPTIONAL) (OPTIONAL)
+  //         \   /
+  //           C
+  schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("A").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("Foo")
+                  .SetDataType(TYPE_STRING)
+                  .SetJoinable(JOINABLE_VALUE_TYPE_QUALIFIED_ID,
+                               /*propagate_delete=*/false)
+                  .SetCardinality(CARDINALITY_OPTIONAL)))
+          .AddType(SchemaTypeConfigBuilder().SetType("B").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("a")
+                  .SetDataTypeDocument("A",
+                                       /*index_nested_properties=*/false)
+                  .SetCardinality(CARDINALITY_REPEATED)))
+          .AddType(SchemaTypeConfigBuilder().SetType("C").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("a")
+                  .SetDataTypeDocument("A",
+                                       /*index_nested_properties=*/false)
+                  .SetCardinality(CARDINALITY_OPTIONAL)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("D")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("b")
+                                        .SetDataTypeDocument(
+                                            "B",
+                                            /*index_nested_properties=*/false)
+                                        .SetCardinality(CARDINALITY_OPTIONAL))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("c")
+                                        .SetDataTypeDocument(
+                                            "C",
+                                            /*index_nested_properties=*/false)
+                                        .SetCardinality(CARDINALITY_OPTIONAL)))
+          .Build();
+  EXPECT_THAT(SchemaUtil::Validate(schema),
+              StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
+
+  //           B
+  //         /   \
+  // (OPTIONAL) (OPTIONAL)
+  //       /       \
+  // D ---           --> A
+  //       \       /
+  // (REPEATED) (OPTIONAL)
+  //         \   /
+  //           C
+  schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("A").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("Foo")
+                  .SetDataType(TYPE_STRING)
+                  .SetJoinable(JOINABLE_VALUE_TYPE_QUALIFIED_ID,
+                               /*propagate_delete=*/false)
+                  .SetCardinality(CARDINALITY_OPTIONAL)))
+          .AddType(SchemaTypeConfigBuilder().SetType("B").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("a")
+                  .SetDataTypeDocument("A",
+                                       /*index_nested_properties=*/false)
+                  .SetCardinality(CARDINALITY_OPTIONAL)))
+          .AddType(SchemaTypeConfigBuilder().SetType("C").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("a")
+                  .SetDataTypeDocument("A",
+                                       /*index_nested_properties=*/false)
+                  .SetCardinality(CARDINALITY_OPTIONAL)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("D")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("b")
+                                        .SetDataTypeDocument(
+                                            "B",
+                                            /*index_nested_properties=*/false)
+                                        .SetCardinality(CARDINALITY_OPTIONAL))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("c")
+                                        .SetDataTypeDocument(
+                                            "C",
+                                            /*index_nested_properties=*/false)
+                                        .SetCardinality(CARDINALITY_REPEATED)))
+          .Build();
+  EXPECT_THAT(SchemaUtil::Validate(schema),
+              StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
+
+  //           B
+  //         /   \
+  // (OPTIONAL) (OPTIONAL)
+  //       /       \
+  // D ---           --> A
+  //       \       /
+  // (OPTIONAL) (REPEATED)
+  //         \   /
+  //           C
+  schema =
+      SchemaBuilder()
+          .AddType(SchemaTypeConfigBuilder().SetType("A").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("Foo")
+                  .SetDataType(TYPE_STRING)
+                  .SetJoinable(JOINABLE_VALUE_TYPE_QUALIFIED_ID,
+                               /*propagate_delete=*/false)
+                  .SetCardinality(CARDINALITY_OPTIONAL)))
+          .AddType(SchemaTypeConfigBuilder().SetType("B").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("a")
+                  .SetDataTypeDocument("A",
+                                       /*index_nested_properties=*/false)
+                  .SetCardinality(CARDINALITY_OPTIONAL)))
+          .AddType(SchemaTypeConfigBuilder().SetType("C").AddProperty(
+              PropertyConfigBuilder()
+                  .SetName("a")
+                  .SetDataTypeDocument("A",
+                                       /*index_nested_properties=*/false)
+                  .SetCardinality(CARDINALITY_REPEATED)))
+          .AddType(SchemaTypeConfigBuilder()
+                       .SetType("D")
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("b")
+                                        .SetDataTypeDocument(
+                                            "B",
+                                            /*index_nested_properties=*/false)
+                                        .SetCardinality(CARDINALITY_OPTIONAL))
+                       .AddProperty(PropertyConfigBuilder()
+                                        .SetName("c")
+                                        .SetDataTypeDocument(
+                                            "C",
+                                            /*index_nested_properties=*/false)
+                                        .SetCardinality(CARDINALITY_OPTIONAL)))
+          .Build();
+  EXPECT_THAT(SchemaUtil::Validate(schema),
+              StatusIs(libtextclassifier3::StatusCode::INVALID_ARGUMENT));
+}
+
 TEST(SchemaUtilTest, MultipleReferencesToSameNestedSchemaOk) {
   SchemaProto schema =
       SchemaBuilder()
diff --git a/icing/store/document-store.cc b/icing/store/document-store.cc
index 35ee172..710ff58 100644
--- a/icing/store/document-store.cc
+++ b/icing/store/document-store.cc
@@ -89,17 +89,6 @@ constexpr int32_t kUriMapperMaxSize = 36 * 1024 * 1024;  // 36 MiB
 constexpr int32_t kNamespaceMapperMaxSize = 3 * 128 * 1024;  // 384 KiB
 constexpr int32_t kCorpusMapperMaxSize = 3 * 128 * 1024;     // 384 KiB
 
-// Whether to use namespace id or namespace name to build up fingerprint for
-// document_key_mapper_ and corpus_mapper_.
-// Note: Changing this flag will require a reconstruction of the internal
-// mappers in the document store. A easy way to trigger a rebuild is to change
-// the kMagic value.
-//
-// TODO(b/259969017) Flip this flag to true at the time when we switch to use
-// persistent hash map for document_key_mapper_ so that we just need one
-// reconstruction of the internal mappers.
-constexpr bool kNamespaceIdFingerprint = false;
-
 DocumentWrapper CreateDocumentWrapper(DocumentProto&& document) {
   DocumentWrapper document_wrapper;
   *document_wrapper.mutable_document() = std::move(document);
@@ -157,23 +146,6 @@ std::string EncodeNamespaceId(NamespaceId namespace_id) {
   return encoding;
 }
 
-std::string MakeFingerprint(NamespaceId namespace_id,
-                            std::string_view namespace_,
-                            std::string_view uri_or_schema) {
-  if (!kNamespaceIdFingerprint) {
-    // Using a 64-bit fingerprint to represent the key could lead to collisions.
-    // But, even with 200K unique keys, the probability of collision is about
-    // one-in-a-billion (https://en.wikipedia.org/wiki/Birthday_attack).
-    uint64_t fprint = tc3farmhash::Fingerprint64(
-        absl_ports::StrCat(namespace_, uri_or_schema));
-    return fingerprint_util::GetFingerprintString(fprint);
-  } else {
-    return absl_ports::StrCat(EncodeNamespaceId(namespace_id),
-                              encode_util::EncodeIntToCString(
-                                  tc3farmhash::Fingerprint64(uri_or_schema)));
-  }
-}
-
 int64_t CalculateExpirationTimestampMs(int64_t creation_timestamp_ms,
                                        int64_t ttl_ms) {
   if (ttl_ms == 0) {
@@ -236,15 +208,34 @@ std::unordered_map<NamespaceId, std::string> GetNamespaceIdsToNamespaces(
 
 }  // namespace
 
+std::string DocumentStore::MakeFingerprint(
+    NamespaceId namespace_id, std::string_view namespace_,
+    std::string_view uri_or_schema) const {
+  if (!namespace_id_fingerprint_) {
+    // Using a 64-bit fingerprint to represent the key could lead to collisions.
+    // But, even with 200K unique keys, the probability of collision is about
+    // one-in-a-billion (https://en.wikipedia.org/wiki/Birthday_attack).
+    uint64_t fprint = tc3farmhash::Fingerprint64(
+        absl_ports::StrCat(namespace_, uri_or_schema));
+    return fingerprint_util::GetFingerprintString(fprint);
+  } else {
+    return absl_ports::StrCat(EncodeNamespaceId(namespace_id),
+                              encode_util::EncodeIntToCString(
+                                  tc3farmhash::Fingerprint64(uri_or_schema)));
+  }
+}
+
 DocumentStore::DocumentStore(const Filesystem* filesystem,
                              const std::string_view base_dir,
                              const Clock* clock,
-                             const SchemaStore* schema_store)
+                             const SchemaStore* schema_store,
+                             bool namespace_id_fingerprint)
     : filesystem_(filesystem),
       base_dir_(base_dir),
       clock_(*clock),
       schema_store_(schema_store),
-      document_validator_(schema_store) {}
+      document_validator_(schema_store),
+      namespace_id_fingerprint_(namespace_id_fingerprint) {}
 
 libtextclassifier3::StatusOr<DocumentId> DocumentStore::Put(
     const DocumentProto& document, int32_t num_tokens,
@@ -271,14 +262,14 @@ DocumentStore::~DocumentStore() {
 libtextclassifier3::StatusOr<DocumentStore::CreateResult> DocumentStore::Create(
     const Filesystem* filesystem, const std::string& base_dir,
     const Clock* clock, const SchemaStore* schema_store,
-    bool force_recovery_and_revalidate_documents,
+    bool force_recovery_and_revalidate_documents, bool namespace_id_fingerprint,
     InitializeStatsProto* initialize_stats) {
   ICING_RETURN_ERROR_IF_NULL(filesystem);
   ICING_RETURN_ERROR_IF_NULL(clock);
   ICING_RETURN_ERROR_IF_NULL(schema_store);
 
-  auto document_store = std::unique_ptr<DocumentStore>(
-      new DocumentStore(filesystem, base_dir, clock, schema_store));
+  auto document_store = std::unique_ptr<DocumentStore>(new DocumentStore(
+      filesystem, base_dir, clock, schema_store, namespace_id_fingerprint));
   ICING_ASSIGN_OR_RETURN(
       DataLoss data_loss,
       document_store->Initialize(force_recovery_and_revalidate_documents,
@@ -386,7 +377,8 @@ libtextclassifier3::Status DocumentStore::InitializeExistingDerivedFiles() {
         absl_ports::StrCat("Couldn't read: ", MakeHeaderFilename(base_dir_)));
   }
 
-  if (header.magic != DocumentStore::Header::kMagic) {
+  if (header.magic !=
+      DocumentStore::Header::GetCurrentMagic(namespace_id_fingerprint_)) {
     return absl_ports::InternalError(absl_ports::StrCat(
         "Invalid header kMagic for file: ", MakeHeaderFilename(base_dir_)));
   }
@@ -859,7 +851,8 @@ bool DocumentStore::HeaderExists() {
 libtextclassifier3::Status DocumentStore::UpdateHeader(const Crc32& checksum) {
   // Write the header
   DocumentStore::Header header;
-  header.magic = DocumentStore::Header::kMagic;
+  header.magic =
+      DocumentStore::Header::GetCurrentMagic(namespace_id_fingerprint_);
   header.checksum = checksum.Get();
 
   // This should overwrite the header.
diff --git a/icing/store/document-store.h b/icing/store/document-store.h
index 3e02636..7c414d7 100644
--- a/icing/store/document-store.h
+++ b/icing/store/document-store.h
@@ -59,13 +59,19 @@ namespace lib {
 class DocumentStore {
  public:
   struct Header {
-    static constexpr int32_t kMagic = 0x746f7265;
+    static int32_t GetCurrentMagic(bool namespace_id_fingerprint) {
+      return namespace_id_fingerprint ? kNewMagic : kOldMagic;
+    }
 
     // Holds the magic as a quick sanity check against file corruption.
     int32_t magic;
 
     // Checksum of the DocumentStore's sub-component's checksums.
     uint32_t checksum;
+
+   private:
+    static constexpr int32_t kOldMagic = 0x746f7265;
+    static constexpr int32_t kNewMagic = 0x1b99c8b0;
   };
 
   struct OptimizeInfo {
@@ -136,6 +142,7 @@ class DocumentStore {
       const Filesystem* filesystem, const std::string& base_dir,
       const Clock* clock, const SchemaStore* schema_store,
       bool force_recovery_and_revalidate_documents = false,
+      bool namespace_id_fingerprint = false,
       InitializeStatsProto* initialize_stats = nullptr);
 
   // Returns the maximum DocumentId that the DocumentStore has assigned. If
@@ -472,7 +479,8 @@ class DocumentStore {
  private:
   // Use DocumentStore::Create() to instantiate.
   DocumentStore(const Filesystem* filesystem, std::string_view base_dir,
-                const Clock* clock, const SchemaStore* schema_store);
+                const Clock* clock, const SchemaStore* schema_store,
+                bool namespace_id_fingerprint);
 
   const Filesystem* const filesystem_;
   const std::string base_dir_;
@@ -485,6 +493,10 @@ class DocumentStore {
   // Used to validate incoming documents
   DocumentValidator document_validator_;
 
+  // Whether to use namespace id or namespace name to build up fingerprint for
+  // document_key_mapper_ and corpus_mapper_.
+  bool namespace_id_fingerprint_;
+
   // A log used to store all documents, it serves as a ground truth of doc
   // store. key_mapper_ and document_id_mapper_ can be regenerated from it.
   std::unique_ptr<PortableFileBackedProtoLog<DocumentWrapper>> document_log_;
@@ -733,6 +745,13 @@ class DocumentStore {
   libtextclassifier3::StatusOr<
       google::protobuf::RepeatedPtrField<DocumentDebugInfoProto::CorpusInfo>>
   CollectCorpusInfo() const;
+
+  // Build fingerprint for the keys of document_key_mapper_ and corpus_mapper_.
+  // Note that namespace_id_fingerprint_ controls the way that a fingerprint is
+  // built.
+  std::string MakeFingerprint(NamespaceId namespace_id,
+                              std::string_view namespace_,
+                              std::string_view uri_or_schema) const;
 };
 
 }  // namespace lib
diff --git a/icing/store/document-store_test.cc b/icing/store/document-store_test.cc
index a115e11..81da191 100644
--- a/icing/store/document-store_test.cc
+++ b/icing/store/document-store_test.cc
@@ -207,7 +207,8 @@ class DocumentStoreTest : public ::testing::Test {
     const std::string header_file =
         absl_ports::StrCat(document_store_dir_, "/document_store_header");
     DocumentStore::Header header;
-    header.magic = DocumentStore::Header::kMagic;
+    header.magic = DocumentStore::Header::GetCurrentMagic(
+        /*namespace_id_fingerprint=*/false);
     header.checksum = 10;  // Arbitrary garbage checksum
     filesystem_.DeleteFile(header_file.c_str());
     filesystem_.Write(header_file.c_str(), &header, sizeof(header));
@@ -3285,10 +3286,10 @@ TEST_F(DocumentStoreTest, LoadScoreCacheAndInitializeSuccessfully) {
   InitializeStatsProto initialize_stats;
   ICING_ASSERT_OK_AND_ASSIGN(
       DocumentStore::CreateResult create_result,
-      DocumentStore::Create(&filesystem_, document_store_dir_, &fake_clock_,
-                            schema_store_.get(),
-                            /*force_recovery_and_revalidate_documents=*/false,
-                            &initialize_stats));
+      DocumentStore::Create(
+          &filesystem_, document_store_dir_, &fake_clock_, schema_store_.get(),
+          /*force_recovery_and_revalidate_documents=*/false,
+          /*namespace_id_fingerprint=*/false, &initialize_stats));
   std::unique_ptr<DocumentStore> doc_store =
       std::move(create_result.document_store);
   // The document log is using the legacy v0 format so that a migration is
@@ -3489,10 +3490,10 @@ TEST_F(DocumentStoreTest, InitializeForceRecoveryUpdatesTypeIds) {
     InitializeStatsProto initialize_stats;
     ICING_ASSERT_OK_AND_ASSIGN(
         DocumentStore::CreateResult create_result,
-        DocumentStore::Create(&filesystem_, document_store_dir_, &fake_clock_,
-                              schema_store.get(),
-                              /*force_recovery_and_revalidate_documents=*/true,
-                              &initialize_stats));
+        DocumentStore::Create(
+            &filesystem_, document_store_dir_, &fake_clock_, schema_store.get(),
+            /*force_recovery_and_revalidate_documents=*/true,
+            /*namespace_id_fingerprint=*/false, &initialize_stats));
     std::unique_ptr<DocumentStore> doc_store =
         std::move(create_result.document_store);
 
@@ -3875,10 +3876,10 @@ TEST_F(DocumentStoreTest, MigrateToPortableFileBackedProtoLog) {
   InitializeStatsProto initialize_stats;
   ICING_ASSERT_OK_AND_ASSIGN(
       DocumentStore::CreateResult create_result,
-      DocumentStore::Create(&filesystem_, document_store_dir, &fake_clock_,
-                            schema_store.get(),
-                            /*force_recovery_and_revalidate_documents=*/false,
-                            &initialize_stats));
+      DocumentStore::Create(
+          &filesystem_, document_store_dir, &fake_clock_, schema_store.get(),
+          /*force_recovery_and_revalidate_documents=*/false,
+          /*namespace_id_fingerprint=*/false, &initialize_stats));
   std::unique_ptr<DocumentStore> document_store =
       std::move(create_result.document_store);
 
diff --git a/icing/tokenization/icu/icu-language-segmenter-factory.cc b/icing/tokenization/icu/icu-language-segmenter-factory.cc
index 363bc6d..7b095b4 100644
--- a/icing/tokenization/icu/icu-language-segmenter-factory.cc
+++ b/icing/tokenization/icu/icu-language-segmenter-factory.cc
@@ -47,7 +47,7 @@ libtextclassifier3::StatusOr<std::unique_ptr<LanguageSegmenter>> Create(
                        << " not supported. Converting to locale " << ULOC_US;
     options.locale = ULOC_US;
   }
-  return std::make_unique<IcuLanguageSegmenter>(std::move(options.locale));
+  return IcuLanguageSegmenter::Create(std::move(options.locale));
 }
 
 }  // namespace language_segmenter_factory
diff --git a/icing/tokenization/icu/icu-language-segmenter.cc b/icing/tokenization/icu/icu-language-segmenter.cc
index fd790cf..59bcc18 100644
--- a/icing/tokenization/icu/icu-language-segmenter.cc
+++ b/icing/tokenization/icu/icu-language-segmenter.cc
@@ -24,6 +24,7 @@
 #include "icing/text_classifier/lib3/utils/base/status.h"
 #include "icing/text_classifier/lib3/utils/base/statusor.h"
 #include "icing/absl_ports/canonical_errors.h"
+#include "icing/absl_ports/mutex.h"
 #include "icing/legacy/core/icing-string-util.h"
 #include "icing/util/character-iterator.h"
 #include "icing/util/i18n-utils.h"
@@ -48,9 +49,11 @@ class IcuLanguageSegmenterIterator : public LanguageSegmenter::Iterator {
   //   INTERNAL_ERROR if unable to create
   static libtextclassifier3::StatusOr<
       std::unique_ptr<LanguageSegmenter::Iterator>>
-  Create(std::string_view text, std::string_view locale) {
+  Create(const IcuLanguageSegmenter* creator, UBreakIterator* break_iterator,
+         std::string_view text, std::string_view locale) {
     std::unique_ptr<IcuLanguageSegmenterIterator> iterator(
-        new IcuLanguageSegmenterIterator(text, locale));
+        new IcuLanguageSegmenterIterator(creator, break_iterator, text,
+                                         locale));
     if (iterator->Initialize()) {
       return iterator;
     }
@@ -58,8 +61,8 @@ class IcuLanguageSegmenterIterator : public LanguageSegmenter::Iterator {
   }
 
   ~IcuLanguageSegmenterIterator() {
-    ubrk_close(break_iterator_);
     utext_close(u_text_);
+    creator_.ReturnBreakIterator(break_iterator_);
   }
 
   // Advances to the next term. Returns false if it has reached the end.
@@ -244,9 +247,12 @@ class IcuLanguageSegmenterIterator : public LanguageSegmenter::Iterator {
   }
 
  private:
-  explicit IcuLanguageSegmenterIterator(std::string_view text,
+  explicit IcuLanguageSegmenterIterator(const IcuLanguageSegmenter* creator,
+                                        UBreakIterator* break_iterator,
+                                        std::string_view text,
                                         std::string_view locale)
-      : break_iterator_(nullptr),
+      : creator_(*creator),
+        break_iterator_(break_iterator),
         text_(text),
         locale_(locale),
         u_text_(nullptr),
@@ -256,13 +262,14 @@ class IcuLanguageSegmenterIterator : public LanguageSegmenter::Iterator {
 
   // Returns true on success
   bool Initialize() {
+    if (break_iterator_ == nullptr) {
+      return false;
+    }
     UErrorCode status = U_ZERO_ERROR;
     u_text_ = utext_openUTF8(nullptr, text_.data(), text_.length(), &status);
     if (u_text_ == nullptr) {
       return false;
     }
-    break_iterator_ = ubrk_open(UBRK_WORD, locale_.data(), /*text=*/nullptr,
-                                /*textLength=*/0, &status);
     ubrk_setUText(break_iterator_, u_text_, &status);
     return !U_FAILURE(status);
   }
@@ -290,9 +297,11 @@ class IcuLanguageSegmenterIterator : public LanguageSegmenter::Iterator {
     term_start_index_ = 0;
   }
 
+  const IcuLanguageSegmenter& creator_;  // Does not own.
+
   // The underlying class that does the segmentation, ubrk_close() must be
   // called after using.
-  UBreakIterator* break_iterator_;
+  UBreakIterator* break_iterator_;  // Does not own
 
   // Text to be segmented
   std::string_view text_;
@@ -321,19 +330,62 @@ class IcuLanguageSegmenterIterator : public LanguageSegmenter::Iterator {
   int term_end_index_exclusive_;
 };
 
-IcuLanguageSegmenter::IcuLanguageSegmenter(std::string locale)
-    : locale_(std::move(locale)) {}
+/* static */ libtextclassifier3::StatusOr<std::unique_ptr<IcuLanguageSegmenter>>
+IcuLanguageSegmenter::Create(std::string&& locale) {
+  UErrorCode status = U_ZERO_ERROR;
+  UBreakIterator* break_iterator = ubrk_open(
+      UBRK_WORD, locale.c_str(), /*text=*/nullptr, /*textLength=*/0, &status);
+  if (U_FAILURE(status) || break_iterator == nullptr) {
+    return absl_ports::AbortedError(
+        "Unable to create ICU break_iterator for language segmentation");
+  }
+  return std::unique_ptr<IcuLanguageSegmenter>(
+      new IcuLanguageSegmenter(std::move(locale), break_iterator));
+}
+
+UBreakIterator* IcuLanguageSegmenter::ProduceBreakIterator() const {
+  UBreakIterator* itr = nullptr;
+  {
+    absl_ports::unique_lock l(&mutex_);
+    if (cached_break_iterator_ != nullptr) {
+      itr = cached_break_iterator_;
+      cached_break_iterator_ = nullptr;
+    }
+  }
+  if (itr == nullptr) {
+    UErrorCode status = U_ZERO_ERROR;
+    itr = ubrk_open(UBRK_WORD, locale_.c_str(), /*text=*/nullptr,
+                    /*textLength=*/0, &status);
+    if (U_FAILURE(status)) {
+      itr = nullptr;
+    }
+  }
+  return itr;
+}
+
+void IcuLanguageSegmenter::ReturnBreakIterator(UBreakIterator* itr) const {
+  {
+    absl_ports::unique_lock l(&mutex_);
+    if (cached_break_iterator_ == nullptr) {
+      cached_break_iterator_ = itr;
+      return;
+    }
+  }
+  ubrk_close(itr);
+}
 
 libtextclassifier3::StatusOr<std::unique_ptr<LanguageSegmenter::Iterator>>
 IcuLanguageSegmenter::Segment(const std::string_view text,
                               LanguageSegmenter::AccessType) const {
-  return IcuLanguageSegmenterIterator::Create(text, locale_);
+  return IcuLanguageSegmenterIterator::Create(this, ProduceBreakIterator(),
+                                              text, locale_);
 }
 
 libtextclassifier3::StatusOr<std::vector<std::string_view>>
 IcuLanguageSegmenter::GetAllTerms(const std::string_view text) const {
-  ICING_ASSIGN_OR_RETURN(std::unique_ptr<LanguageSegmenter::Iterator> iterator,
-                         IcuLanguageSegmenterIterator::Create(text, locale_));
+  ICING_ASSIGN_OR_RETURN(
+      std::unique_ptr<LanguageSegmenter::Iterator> iterator,
+      Segment(text, LanguageSegmenter::AccessType::kForwardIterator));
   std::vector<std::string_view> terms;
   while (iterator->Advance()) {
     terms.push_back(iterator->GetTerm());
diff --git a/icing/tokenization/icu/icu-language-segmenter.h b/icing/tokenization/icu/icu-language-segmenter.h
index f9cfbcb..e22c5d2 100644
--- a/icing/tokenization/icu/icu-language-segmenter.h
+++ b/icing/tokenization/icu/icu-language-segmenter.h
@@ -22,7 +22,9 @@
 #include <vector>
 
 #include "icing/text_classifier/lib3/utils/base/statusor.h"
+#include "icing/absl_ports/mutex.h"
 #include "icing/tokenization/language-segmenter.h"
+#include "unicode/ubrk.h"
 
 namespace icing {
 namespace lib {
@@ -41,7 +43,14 @@ namespace lib {
 // class. Other special tokenization logic will be in each tokenizer.
 class IcuLanguageSegmenter : public LanguageSegmenter {
  public:
-  explicit IcuLanguageSegmenter(std::string locale);
+  static libtextclassifier3::StatusOr<std::unique_ptr<IcuLanguageSegmenter>>
+  Create(std::string&& locale);
+
+  ~IcuLanguageSegmenter() override {
+    if (cached_break_iterator_ != nullptr) {
+      ubrk_close(cached_break_iterator_);
+    }
+  }
 
   IcuLanguageSegmenter(const IcuLanguageSegmenter&) = delete;
   IcuLanguageSegmenter& operator=(const IcuLanguageSegmenter&) = delete;
@@ -69,8 +78,32 @@ class IcuLanguageSegmenter : public LanguageSegmenter {
       std::string_view text) const override;
 
  private:
+  // Declared a friend so that it can call AcceptBreakIterator.
+  friend class IcuLanguageSegmenterIterator;
+
+  explicit IcuLanguageSegmenter(std::string&& locale, UBreakIterator* iterator)
+      : locale_(std::move(locale)), cached_break_iterator_(iterator) {}
+
+  // Returns a UBreakIterator that the caller owns.
+  // If cached_break_iterator_ is non-null, transfers ownership to caller and
+  // sets cached_break_iterator_ to null.
+  // If cached_break_iterator is null, creates a new UBreakIterator and
+  // transfers ownership to caller.
+  UBreakIterator* ProduceBreakIterator() const;
+
+  // Caller transfers ownership of itr to IcuLanguageSegmenter.
+  // If cached_break_iterator_ is null, itr becomes the cached_break_iterator_
+  // If cached_break_iterator_ is non-null, then itr will be closed.
+  void ReturnBreakIterator(UBreakIterator* itr) const;
+
   // Used to help segment text
   const std::string locale_;
+
+  // The underlying class that does the segmentation, ubrk_close() must be
+  // called after using.
+  mutable UBreakIterator* cached_break_iterator_ ICING_LOCKS_EXCLUDED(mutex_);
+
+  mutable absl_ports::shared_mutex mutex_;
 };
 
 }  // namespace lib
diff --git a/icing/tokenization/icu/icu-language-segmenter_test.cc b/icing/tokenization/icu/icu-language-segmenter_test.cc
index c88b992..d1bf5c6 100644
--- a/icing/tokenization/icu/icu-language-segmenter_test.cc
+++ b/icing/tokenization/icu/icu-language-segmenter_test.cc
@@ -1352,6 +1352,53 @@ TEST_P(IcuLanguageSegmenterAllLocalesTest, QuerySyntax) {
                                  "subproperty2", ":", "term3"));
 }
 
+TEST_P(IcuLanguageSegmenterAllLocalesTest, MultipleLangSegmentersTest) {
+  ICING_ASSERT_OK_AND_ASSIGN(
+      auto language_segmenter,
+      language_segmenter_factory::Create(
+          GetSegmenterOptions(GetLocale(), jni_cache_.get())));
+
+  ICING_ASSERT_OK_AND_ASSIGN(
+      std::unique_ptr<LanguageSegmenter::Iterator> iterator_one,
+      language_segmenter->Segment(
+          "foo bar baz", LanguageSegmenter::AccessType::kForwardIterator));
+  ICING_ASSERT_OK_AND_ASSIGN(
+      std::unique_ptr<LanguageSegmenter::Iterator> iterator_two,
+      language_segmenter->Segment(
+          "abra kadabra alakazam",
+          LanguageSegmenter::AccessType::kForwardIterator));
+
+  ASSERT_TRUE(iterator_one->Advance());
+  ASSERT_TRUE(iterator_two->Advance());
+  EXPECT_THAT(iterator_one->GetTerm(), Eq("foo"));
+  EXPECT_THAT(iterator_two->GetTerm(), Eq("abra"));
+
+  ASSERT_TRUE(iterator_one->Advance());
+  ASSERT_TRUE(iterator_two->Advance());
+  EXPECT_THAT(iterator_one->GetTerm(), Eq(" "));
+  EXPECT_THAT(iterator_two->GetTerm(), Eq(" "));
+
+  ASSERT_TRUE(iterator_one->Advance());
+  EXPECT_THAT(iterator_one->GetTerm(), Eq("bar"));
+  EXPECT_THAT(iterator_two->GetTerm(), Eq(" "));
+  ASSERT_TRUE(iterator_two->Advance());
+  EXPECT_THAT(iterator_one->GetTerm(), Eq("bar"));
+  EXPECT_THAT(iterator_two->GetTerm(), Eq("kadabra"));
+
+  ASSERT_TRUE(iterator_one->Advance());
+  ASSERT_TRUE(iterator_two->Advance());
+  EXPECT_THAT(iterator_one->GetTerm(), Eq(" "));
+  EXPECT_THAT(iterator_two->GetTerm(), Eq(" "));
+
+  ASSERT_TRUE(iterator_two->Advance());
+  ASSERT_TRUE(iterator_one->Advance());
+  EXPECT_THAT(iterator_one->GetTerm(), Eq("baz"));
+  EXPECT_THAT(iterator_two->GetTerm(), Eq("alakazam"));
+
+  ASSERT_FALSE(iterator_two->Advance());
+  ASSERT_FALSE(iterator_one->Advance());
+}
+
 INSTANTIATE_TEST_SUITE_P(
     LocaleName, IcuLanguageSegmenterAllLocalesTest,
     testing::Values(ULOC_US, ULOC_UK, ULOC_CANADA, ULOC_CANADA_FRENCH,
diff --git a/icing/tokenization/rfc822-tokenizer_test.cc b/icing/tokenization/rfc822-tokenizer_test.cc
index 6b95a07..e1a7fc8 100644
--- a/icing/tokenization/rfc822-tokenizer_test.cc
+++ b/icing/tokenization/rfc822-tokenizer_test.cc
@@ -21,10 +21,7 @@
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 #include "icing/testing/common-matchers.h"
-#include "icing/testing/jni-test-helpers.h"
-#include "icing/tokenization/language-segmenter-factory.h"
 #include "icing/tokenization/language-segmenter.h"
-#include "unicode/uloc.h"
 
 namespace icing {
 namespace lib {
@@ -32,21 +29,7 @@ namespace {
 using ::testing::ElementsAre;
 using ::testing::IsEmpty;
 
-class Rfc822TokenizerTest : public testing::Test {
- protected:
-  void SetUp() override {
-    jni_cache_ = GetTestJniCache();
-    language_segmenter_factory::SegmenterOptions options(ULOC_US,
-                                                         jni_cache_.get());
-    ICING_ASSERT_OK_AND_ASSIGN(
-        language_segmenter_,
-        language_segmenter_factory::Create(std::move(options)));
-  }
-  std::unique_ptr<const JniCache> jni_cache_;
-  std::unique_ptr<LanguageSegmenter> language_segmenter_;
-};
-
-TEST_F(Rfc822TokenizerTest, StartingState) {
+TEST(Rfc822TokenizerTest, StartingState) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
   std::string text = "a@g.c";
   auto token_iterator =
@@ -59,7 +42,7 @@ TEST_F(Rfc822TokenizerTest, StartingState) {
   ASSERT_THAT(token_iterator->GetTokens(), Not(IsEmpty()));
 }
 
-TEST_F(Rfc822TokenizerTest, EmptyMiddleToken) {
+TEST(Rfc822TokenizerTest, EmptyMiddleToken) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
 
   std::string s("<alex>,,<tom>");
@@ -77,7 +60,7 @@ TEST_F(Rfc822TokenizerTest, EmptyMiddleToken) {
           EqualsToken(Token::Type::RFC822_ADDRESS_COMPONENT_HOST, "tom"))));
 }
 
-TEST_F(Rfc822TokenizerTest, Simple) {
+TEST(Rfc822TokenizerTest, Simple) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
 
   std::string_view s("<你alex@google.com>");
@@ -94,7 +77,7 @@ TEST_F(Rfc822TokenizerTest, Simple) {
           EqualsToken(Token::Type::RFC822_ADDRESS_COMPONENT_HOST, "com"))));
 }
 
-TEST_F(Rfc822TokenizerTest, Small) {
+TEST(Rfc822TokenizerTest, Small) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
 
   std::string s = "\"a\"";
@@ -127,7 +110,7 @@ TEST_F(Rfc822TokenizerTest, Small) {
                                EqualsToken(Token::Type::RFC822_COMMENT, "a"))));
 }
 
-TEST_F(Rfc822TokenizerTest, PB) {
+TEST(Rfc822TokenizerTest, PB) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
 
   std::string_view s("peanut (comment) butter, <alex@google.com>");
@@ -154,7 +137,7 @@ TEST_F(Rfc822TokenizerTest, PB) {
           EqualsToken(Token::Type::RFC822_ADDRESS_COMPONENT_HOST, "com"))));
 }
 
-TEST_F(Rfc822TokenizerTest, NoBrackets) {
+TEST(Rfc822TokenizerTest, NoBrackets) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
 
   std::string_view s("alex@google.com");
@@ -171,7 +154,7 @@ TEST_F(Rfc822TokenizerTest, NoBrackets) {
           EqualsToken(Token::Type::RFC822_HOST_ADDRESS, "google.com"))));
 }
 
-TEST_F(Rfc822TokenizerTest, TwoAddresses) {
+TEST(Rfc822TokenizerTest, TwoAddresses) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
 
   std::string_view s("<你alex@google.com>; <alexsav@gmail.com>");
@@ -195,7 +178,7 @@ TEST_F(Rfc822TokenizerTest, TwoAddresses) {
           EqualsToken(Token::Type::RFC822_ADDRESS_COMPONENT_HOST, "com"))));
 }
 
-TEST_F(Rfc822TokenizerTest, Comment) {
+TEST(Rfc822TokenizerTest, Comment) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
 
   std::string_view s("(a comment) <alex@google.com>");
@@ -214,7 +197,7 @@ TEST_F(Rfc822TokenizerTest, Comment) {
           EqualsToken(Token::Type::RFC822_ADDRESS_COMPONENT_HOST, "com"))));
 }
 
-TEST_F(Rfc822TokenizerTest, NameAndComment) {
+TEST(Rfc822TokenizerTest, NameAndComment) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
 
   std::string_view s("\"a name\" also a name <alex@google.com>");
@@ -237,7 +220,7 @@ TEST_F(Rfc822TokenizerTest, NameAndComment) {
 }
 
 // Test from tokenizer_test.cc.
-TEST_F(Rfc822TokenizerTest, Rfc822SanityCheck) {
+TEST(Rfc822TokenizerTest, Rfc822SanityCheck) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
 
   std::string addr1("A name (A comment) <address@domain.com>");
@@ -297,7 +280,7 @@ TEST_F(Rfc822TokenizerTest, Rfc822SanityCheck) {
 }
 
 // Tests from rfc822 converter.
-TEST_F(Rfc822TokenizerTest, SimpleRfcText) {
+TEST(Rfc822TokenizerTest, SimpleRfcText) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
   std::string test_string =
       "foo@google.com,bar@google.com,baz@google.com,foo+hello@google.com,baz@"
@@ -349,7 +332,7 @@ TEST_F(Rfc822TokenizerTest, SimpleRfcText) {
           EqualsToken(Token::Type::RFC822_HOST_ADDRESS, "corp.google.com"))));
 }
 
-TEST_F(Rfc822TokenizerTest, ComplicatedRfcText) {
+TEST(Rfc822TokenizerTest, ComplicatedRfcText) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
   std::string test_string =
       R"raw("Weird, But&(Also)\\Valid" Name (!With, "an" \\odd\\ cmt too¡) <Foo B(a)r,Baz@g.co>
@@ -390,7 +373,7 @@ TEST_F(Rfc822TokenizerTest, ComplicatedRfcText) {
           EqualsToken(Token::Type::RFC822_ADDRESS_COMPONENT_HOST, "com"))));
 }
 
-TEST_F(Rfc822TokenizerTest, FromHtmlBugs) {
+TEST(Rfc822TokenizerTest, FromHtmlBugs) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
   // This input used to cause HTML parsing exception. We don't do HTML parsing
   // any more (b/8388100) so we are just checking that it does not crash and
@@ -422,7 +405,7 @@ TEST_F(Rfc822TokenizerTest, FromHtmlBugs) {
           EqualsToken(Token::Type::RFC822_ADDRESS_COMPONENT_HOST, "com"))));
 }
 
-TEST_F(Rfc822TokenizerTest, EmptyComponentsTest) {
+TEST(Rfc822TokenizerTest, EmptyComponentsTest) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
   EXPECT_THAT(rfc822_tokenizer.TokenizeAll(""),
               IsOkAndHolds(testing::IsEmpty()));
@@ -463,7 +446,7 @@ TEST_F(Rfc822TokenizerTest, EmptyComponentsTest) {
                   EqualsToken(Token::Type::RFC822_COMMENT, "comment"))));
 }
 
-TEST_F(Rfc822TokenizerTest, NameTest) {
+TEST(Rfc822TokenizerTest, NameTest) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
 
   // Name spread between address or comment.
@@ -529,7 +512,7 @@ TEST_F(Rfc822TokenizerTest, NameTest) {
           EqualsToken(Token::Type::RFC822_ADDRESS_COMPONENT_HOST, "addr"))));
 }
 
-TEST_F(Rfc822TokenizerTest, CommentEscapeTest) {
+TEST(Rfc822TokenizerTest, CommentEscapeTest) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
   // '(', ')', '\\' chars should be escaped. All other escaped chars should be
   // unescaped.
@@ -564,7 +547,7 @@ TEST_F(Rfc822TokenizerTest, CommentEscapeTest) {
           EqualsToken(Token::Type::RFC822_HOST_ADDRESS, "name"))));
 }
 
-TEST_F(Rfc822TokenizerTest, QuoteEscapeTest) {
+TEST(Rfc822TokenizerTest, QuoteEscapeTest) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
   // All names that include non-alphanumeric chars must be quoted and have '\\'
   // and '"' chars escaped.
@@ -593,7 +576,7 @@ TEST_F(Rfc822TokenizerTest, QuoteEscapeTest) {
           EqualsToken(Token::Type::RFC822_HOST_ADDRESS, R"(n\\a\m\"e)"))));
 }
 
-TEST_F(Rfc822TokenizerTest, UnterminatedComponentTest) {
+TEST(Rfc822TokenizerTest, UnterminatedComponentTest) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
 
   EXPECT_THAT(
@@ -661,7 +644,7 @@ TEST_F(Rfc822TokenizerTest, UnterminatedComponentTest) {
           EqualsToken(Token::Type::RFC822_COMMENT, "comment"))));
 }
 
-TEST_F(Rfc822TokenizerTest, Tokenize) {
+TEST(Rfc822TokenizerTest, Tokenize) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
 
   std::string text =
@@ -714,7 +697,7 @@ TEST_F(Rfc822TokenizerTest, Tokenize) {
           EqualsToken(Token::Type::RFC822_COMMENT, "something"))));
 }
 
-TEST_F(Rfc822TokenizerTest, EdgeCases) {
+TEST(Rfc822TokenizerTest, EdgeCases) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
 
   // Text to trigger the scenario where you have a non-alphabetic followed
@@ -776,7 +759,7 @@ TEST_F(Rfc822TokenizerTest, EdgeCases) {
           EqualsToken(Token::Type::RFC822_ADDRESS_COMPONENT_HOST, "com"))));
 }
 
-TEST_F(Rfc822TokenizerTest, NumberInAddress) {
+TEST(Rfc822TokenizerTest, NumberInAddress) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
   std::string text = "<3alex@google.com>";
   EXPECT_THAT(
@@ -791,7 +774,7 @@ TEST_F(Rfc822TokenizerTest, NumberInAddress) {
           EqualsToken(Token::Type::RFC822_ADDRESS_COMPONENT_HOST, "com"))));
 }
 
-TEST_F(Rfc822TokenizerTest, DoubleQuoteDoubleSlash) {
+TEST(Rfc822TokenizerTest, DoubleQuoteDoubleSlash) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
   std::string text = R"("alex\"")";
   EXPECT_THAT(
@@ -813,7 +796,7 @@ TEST_F(Rfc822TokenizerTest, DoubleQuoteDoubleSlash) {
           EqualsToken(Token::Type::RFC822_HOST_ADDRESS, R"(alex\\\a)"))));
 }
 
-TEST_F(Rfc822TokenizerTest, TwoEmails) {
+TEST(Rfc822TokenizerTest, TwoEmails) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
   std::string text = "tjbarron@google.com alexsav@google.com";
   EXPECT_THAT(
@@ -835,7 +818,7 @@ TEST_F(Rfc822TokenizerTest, TwoEmails) {
           EqualsToken(Token::Type::RFC822_HOST_ADDRESS, "google.com"))));
 }
 
-TEST_F(Rfc822TokenizerTest, BackSlashes) {
+TEST(Rfc822TokenizerTest, BackSlashes) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
   std::string text = R"("\name")";
   EXPECT_THAT(
@@ -859,7 +842,7 @@ TEST_F(Rfc822TokenizerTest, BackSlashes) {
           EqualsToken(Token::Type::RFC822_HOST_ADDRESS, "foo\\@gmail"))));
 }
 
-TEST_F(Rfc822TokenizerTest, BigWhitespace) {
+TEST(Rfc822TokenizerTest, BigWhitespace) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
   std::string text = "\"quoted\"              <address>";
   EXPECT_THAT(
@@ -872,7 +855,7 @@ TEST_F(Rfc822TokenizerTest, BigWhitespace) {
           EqualsToken(Token::Type::RFC822_ADDRESS_COMPONENT_HOST, "address"))));
 }
 
-TEST_F(Rfc822TokenizerTest, AtSignFirst) {
+TEST(Rfc822TokenizerTest, AtSignFirst) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
   std::string text = "\"@foo\"";
   EXPECT_THAT(
@@ -884,7 +867,7 @@ TEST_F(Rfc822TokenizerTest, AtSignFirst) {
           EqualsToken(Token::Type::RFC822_HOST_ADDRESS, "foo"))));
 }
 
-TEST_F(Rfc822TokenizerTest, SlashThenUnicode) {
+TEST(Rfc822TokenizerTest, SlashThenUnicode) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
   std::string text = R"("quoted\你cjk")";
   EXPECT_THAT(
@@ -897,7 +880,7 @@ TEST_F(Rfc822TokenizerTest, SlashThenUnicode) {
           EqualsToken(Token::Type::RFC822_HOST_ADDRESS, "quoted\\你cjk"))));
 }
 
-TEST_F(Rfc822TokenizerTest, AddressEmptyAddress) {
+TEST(Rfc822TokenizerTest, AddressEmptyAddress) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
   std::string text = "<address> <> Name";
   EXPECT_THAT(
@@ -910,7 +893,7 @@ TEST_F(Rfc822TokenizerTest, AddressEmptyAddress) {
           EqualsToken(Token::Type::RFC822_NAME, "Name"))));
 }
 
-TEST_F(Rfc822TokenizerTest, ProperComment) {
+TEST(Rfc822TokenizerTest, ProperComment) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
   std::string text = "(comment)alex@google.com";
   EXPECT_THAT(
@@ -926,7 +909,7 @@ TEST_F(Rfc822TokenizerTest, ProperComment) {
           EqualsToken(Token::Type::RFC822_HOST_ADDRESS, "google.com"))));
 }
 
-TEST_F(Rfc822TokenizerTest, SmallNameToEmail) {
+TEST(Rfc822TokenizerTest, SmallNameToEmail) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
   std::string text = "a@g.c,b@g.c";
   EXPECT_THAT(rfc822_tokenizer.TokenizeAll(text),
@@ -958,7 +941,7 @@ TEST_F(Rfc822TokenizerTest, SmallNameToEmail) {
                   EqualsToken(Token::Type::RFC822_HOST_ADDRESS, "g.c"))));
 }
 
-TEST_F(Rfc822TokenizerTest, AtSignLast) {
+TEST(Rfc822TokenizerTest, AtSignLast) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
   std::string_view text("<alex@>, tim@");
   EXPECT_THAT(
@@ -974,13 +957,13 @@ TEST_F(Rfc822TokenizerTest, AtSignLast) {
           EqualsToken(Token::Type::RFC822_LOCAL_ADDRESS, "tim"))));
 }
 
-TEST_F(Rfc822TokenizerTest, Commas) {
+TEST(Rfc822TokenizerTest, Commas) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
   std::string text = ",,,,,,,,,,,,,,,,,,,,,,,,,,;";
   EXPECT_THAT(rfc822_tokenizer.TokenizeAll(text), IsOkAndHolds(IsEmpty()));
 }
 
-TEST_F(Rfc822TokenizerTest, ResetToTokenStartingAfter) {
+TEST(Rfc822TokenizerTest, ResetToTokenStartingAfter) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
   std::string text = "a@g.c,b@g.c";
   auto token_iterator =
@@ -999,7 +982,7 @@ TEST_F(Rfc822TokenizerTest, ResetToTokenStartingAfter) {
   ASSERT_FALSE(token_iterator->ResetToTokenStartingAfter(6));
 }
 
-TEST_F(Rfc822TokenizerTest, ResetToTokenEndingBefore) {
+TEST(Rfc822TokenizerTest, ResetToTokenEndingBefore) {
   Rfc822Tokenizer rfc822_tokenizer = Rfc822Tokenizer();
   std::string text = "a@g.c,b@g.c";
   auto token_iterator =
diff --git a/icing/util/tokenized-document.cc b/icing/util/tokenized-document.cc
index 1c11c3c..004181e 100644
--- a/icing/util/tokenized-document.cc
+++ b/icing/util/tokenized-document.cc
@@ -20,6 +20,7 @@
 
 #include "icing/text_classifier/lib3/utils/base/status.h"
 #include "icing/proto/document.pb.h"
+#include "icing/schema/joinable-property.h"
 #include "icing/schema/schema-store.h"
 #include "icing/schema/section.h"
 #include "icing/tokenization/language-segmenter.h"
@@ -74,6 +75,9 @@ TokenizedDocument::Create(const SchemaStore* schema_store,
   ICING_ASSIGN_OR_RETURN(SectionGroup section_group,
                          schema_store->ExtractSections(document));
 
+  ICING_ASSIGN_OR_RETURN(JoinablePropertyGroup joinable_property_group,
+                         schema_store->ExtractJoinableProperties(document));
+
   // Tokenize string sections
   ICING_ASSIGN_OR_RETURN(
       std::vector<TokenizedSection> tokenized_string_sections,
@@ -82,7 +86,8 @@ TokenizedDocument::Create(const SchemaStore* schema_store,
 
   return TokenizedDocument(std::move(document),
                            std::move(tokenized_string_sections),
-                           std::move(section_group.integer_sections));
+                           std::move(section_group.integer_sections),
+                           std::move(joinable_property_group));
 }
 
 }  // namespace lib
diff --git a/icing/util/tokenized-document.h b/icing/util/tokenized-document.h
index 5729df2..7cc34e3 100644
--- a/icing/util/tokenized-document.h
+++ b/icing/util/tokenized-document.h
@@ -21,6 +21,7 @@
 
 #include "icing/text_classifier/lib3/utils/base/statusor.h"
 #include "icing/proto/document.pb.h"
+#include "icing/schema/joinable-property.h"
 #include "icing/schema/schema-store.h"
 #include "icing/schema/section.h"
 #include "icing/tokenization/language-segmenter.h"
@@ -62,19 +63,27 @@ class TokenizedDocument {
     return integer_sections_;
   }
 
+  const std::vector<JoinableProperty<std::string_view>>&
+  qualified_id_join_properties() const {
+    return joinable_property_group_.qualified_id_properties;
+  }
+
  private:
   // Use TokenizedDocument::Create() to instantiate.
   explicit TokenizedDocument(
       DocumentProto&& document,
       std::vector<TokenizedSection>&& tokenized_string_sections,
-      std::vector<Section<int64_t>>&& integer_sections)
+      std::vector<Section<int64_t>>&& integer_sections,
+      JoinablePropertyGroup&& joinable_property_group)
       : document_(std::move(document)),
         tokenized_string_sections_(std::move(tokenized_string_sections)),
-        integer_sections_(std::move(integer_sections)) {}
+        integer_sections_(std::move(integer_sections)),
+        joinable_property_group_(std::move(joinable_property_group)) {}
 
   DocumentProto document_;
   std::vector<TokenizedSection> tokenized_string_sections_;
   std::vector<Section<int64_t>> integer_sections_;
+  JoinablePropertyGroup joinable_property_group_;
 };
 
 }  // namespace lib
diff --git a/icing/util/tokenized-document_test.cc b/icing/util/tokenized-document_test.cc
index 3497bef..f2a9214 100644
--- a/icing/util/tokenized-document_test.cc
+++ b/icing/util/tokenized-document_test.cc
@@ -27,6 +27,7 @@
 #include "icing/proto/schema.pb.h"
 #include "icing/proto/term.pb.h"
 #include "icing/schema-builder.h"
+#include "icing/schema/joinable-property.h"
 #include "icing/schema/schema-store.h"
 #include "icing/schema/section.h"
 #include "icing/testing/common-matchers.h"
@@ -50,19 +51,29 @@ using ::testing::IsEmpty;
 using ::testing::SizeIs;
 
 // schema types
-constexpr std::string_view kFakeType = "FakeType";
+static constexpr std::string_view kFakeType = "FakeType";
 
 // Indexable properties and section Id. Section Id is determined by the
 // lexicographical order of indexable property path.
-constexpr std::string_view kIndexableIntegerProperty1 = "indexableInteger1";
-constexpr std::string_view kIndexableIntegerProperty2 = "indexableInteger2";
-constexpr std::string_view kStringExactProperty = "stringExact";
-constexpr std::string_view kStringPrefixProperty = "stringPrefix";
-
-constexpr SectionId kIndexableInteger1SectionId = 0;
-constexpr SectionId kIndexableInteger2SectionId = 1;
-constexpr SectionId kStringExactSectionId = 2;
-constexpr SectionId kStringPrefixSectionId = 3;
+static constexpr std::string_view kIndexableIntegerProperty1 =
+    "indexableInteger1";
+static constexpr std::string_view kIndexableIntegerProperty2 =
+    "indexableInteger2";
+static constexpr std::string_view kStringExactProperty = "stringExact";
+static constexpr std::string_view kStringPrefixProperty = "stringPrefix";
+
+static constexpr SectionId kIndexableInteger1SectionId = 0;
+static constexpr SectionId kIndexableInteger2SectionId = 1;
+static constexpr SectionId kStringExactSectionId = 2;
+static constexpr SectionId kStringPrefixSectionId = 3;
+
+// Joinable properties and joinable property id. Joinable property id is
+// determined by the lexicographical order of joinable property path.
+static constexpr std::string_view kQualifiedId1 = "qualifiedId1";
+static constexpr std::string_view kQualifiedId2 = "qualifiedId2";
+
+static constexpr JoinablePropertyId kQualifiedId1JoinablePropertyId = 0;
+static constexpr JoinablePropertyId kQualifiedId2JoinablePropertyId = 1;
 
 const SectionMetadata kIndexableInteger1SectionMetadata(
     kIndexableInteger1SectionId, TYPE_INT64, TOKENIZER_NONE, TERM_MATCH_UNKNOWN,
@@ -80,7 +91,15 @@ const SectionMetadata kStringPrefixSectionMetadata(
     kStringPrefixSectionId, TYPE_STRING, TOKENIZER_PLAIN, TERM_MATCH_PREFIX,
     NUMERIC_MATCH_UNKNOWN, std::string(kStringPrefixProperty));
 
-// Other non-indexable properties.
+const JoinablePropertyMetadata kQualifiedId1JoinablePropertyMetadata(
+    kQualifiedId1JoinablePropertyId, TYPE_STRING,
+    JOINABLE_VALUE_TYPE_QUALIFIED_ID, std::string(kQualifiedId1));
+
+const JoinablePropertyMetadata kQualifiedId2JoinablePropertyMetadata(
+    kQualifiedId2JoinablePropertyId, TYPE_STRING,
+    JOINABLE_VALUE_TYPE_QUALIFIED_ID, std::string(kQualifiedId2));
+
+// Other non-indexable/joinable properties.
 constexpr std::string_view kUnindexedStringProperty = "unindexedString";
 constexpr std::string_view kUnindexedIntegerProperty = "unindexedInteger";
 
@@ -137,6 +156,16 @@ class TokenizedDocumentTest : public ::testing::Test {
                                      .SetName(kStringPrefixProperty)
                                      .SetDataTypeString(TERM_MATCH_PREFIX,
                                                         TOKENIZER_PLAIN)
+                                     .SetCardinality(CARDINALITY_OPTIONAL))
+                    .AddProperty(PropertyConfigBuilder()
+                                     .SetName(kQualifiedId1)
+                                     .SetDataTypeJoinableString(
+                                         JOINABLE_VALUE_TYPE_QUALIFIED_ID)
+                                     .SetCardinality(CARDINALITY_OPTIONAL))
+                    .AddProperty(PropertyConfigBuilder()
+                                     .SetName(kQualifiedId2)
+                                     .SetDataTypeJoinableString(
+                                         JOINABLE_VALUE_TYPE_QUALIFIED_ID)
                                      .SetCardinality(CARDINALITY_OPTIONAL)))
             .Build();
     ICING_ASSERT_OK(schema_store_->SetSchema(schema));
@@ -177,6 +206,8 @@ TEST_F(TokenizedDocumentTest, CreateAll) {
           .AddInt64Property(std::string(kUnindexedIntegerProperty), 789)
           .AddInt64Property(std::string(kIndexableIntegerProperty1), 1, 2, 3)
           .AddInt64Property(std::string(kIndexableIntegerProperty2), 456)
+          .AddStringProperty(std::string(kQualifiedId1), "pkg$db/ns#uri1")
+          .AddStringProperty(std::string(kQualifiedId2), "pkg$db/ns#uri2")
           .Build();
 
   ICING_ASSERT_OK_AND_ASSIGN(
@@ -210,6 +241,17 @@ TEST_F(TokenizedDocumentTest, CreateAll) {
               Eq(kIndexableInteger2SectionMetadata));
   EXPECT_THAT(tokenized_document.integer_sections().at(1).content,
               ElementsAre(456));
+
+  // Qualified id join properties
+  EXPECT_THAT(tokenized_document.qualified_id_join_properties(), SizeIs(2));
+  EXPECT_THAT(tokenized_document.qualified_id_join_properties().at(0).metadata,
+              Eq(kQualifiedId1JoinablePropertyMetadata));
+  EXPECT_THAT(tokenized_document.qualified_id_join_properties().at(0).values,
+              ElementsAre("pkg$db/ns#uri1"));
+  EXPECT_THAT(tokenized_document.qualified_id_join_properties().at(1).metadata,
+              Eq(kQualifiedId2JoinablePropertyMetadata));
+  EXPECT_THAT(tokenized_document.qualified_id_join_properties().at(1).values,
+              ElementsAre("pkg$db/ns#uri2"));
 }
 
 TEST_F(TokenizedDocumentTest, CreateNoIndexableIntegerProperties) {
@@ -233,6 +275,9 @@ TEST_F(TokenizedDocumentTest, CreateNoIndexableIntegerProperties) {
 
   // integer sections
   EXPECT_THAT(tokenized_document.integer_sections(), IsEmpty());
+
+  // Qualified id join properties
+  EXPECT_THAT(tokenized_document.qualified_id_join_properties(), IsEmpty());
 }
 
 TEST_F(TokenizedDocumentTest, CreateMultipleIndexableIntegerProperties) {
@@ -266,6 +311,9 @@ TEST_F(TokenizedDocumentTest, CreateMultipleIndexableIntegerProperties) {
               Eq(kIndexableInteger2SectionMetadata));
   EXPECT_THAT(tokenized_document.integer_sections().at(1).content,
               ElementsAre(456));
+
+  // Qualified id join properties
+  EXPECT_THAT(tokenized_document.qualified_id_join_properties(), IsEmpty());
 }
 
 TEST_F(TokenizedDocumentTest, CreateNoIndexableStringProperties) {
@@ -290,6 +338,9 @@ TEST_F(TokenizedDocumentTest, CreateNoIndexableStringProperties) {
 
   // integer sections
   EXPECT_THAT(tokenized_document.integer_sections(), IsEmpty());
+
+  // Qualified id join properties
+  EXPECT_THAT(tokenized_document.qualified_id_join_properties(), IsEmpty());
 }
 
 TEST_F(TokenizedDocumentTest, CreateMultipleIndexableStringProperties) {
@@ -327,6 +378,73 @@ TEST_F(TokenizedDocumentTest, CreateMultipleIndexableStringProperties) {
 
   // integer sections
   EXPECT_THAT(tokenized_document.integer_sections(), IsEmpty());
+
+  // Qualified id join properties
+  EXPECT_THAT(tokenized_document.qualified_id_join_properties(), IsEmpty());
+}
+
+TEST_F(TokenizedDocumentTest, CreateNoJoinQualifiedIdProperties) {
+  DocumentProto document =
+      DocumentBuilder()
+          .SetKey("icing", "fake_type/1")
+          .SetSchema(std::string(kFakeType))
+          .AddStringProperty(std::string(kUnindexedStringProperty),
+                             "hello world unindexed")
+          .Build();
+
+  ICING_ASSERT_OK_AND_ASSIGN(
+      TokenizedDocument tokenized_document,
+      TokenizedDocument::Create(schema_store_.get(), lang_segmenter_.get(),
+                                document));
+
+  EXPECT_THAT(tokenized_document.document(), EqualsProto(document));
+  EXPECT_THAT(tokenized_document.num_string_tokens(), Eq(0));
+
+  // string sections
+  EXPECT_THAT(tokenized_document.tokenized_string_sections(), IsEmpty());
+
+  // integer sections
+  EXPECT_THAT(tokenized_document.integer_sections(), IsEmpty());
+
+  // Qualified id join properties
+  EXPECT_THAT(tokenized_document.qualified_id_join_properties(), IsEmpty());
+}
+
+TEST_F(TokenizedDocumentTest, CreateMultipleJoinQualifiedIdProperties) {
+  DocumentProto document =
+      DocumentBuilder()
+          .SetKey("icing", "fake_type/1")
+          .SetSchema(std::string(kFakeType))
+          .AddStringProperty(std::string(kUnindexedStringProperty),
+                             "hello world unindexed")
+          .AddStringProperty(std::string(kQualifiedId1), "pkg$db/ns#uri1")
+          .AddStringProperty(std::string(kQualifiedId2), "pkg$db/ns#uri2")
+          .Build();
+
+  ICING_ASSERT_OK_AND_ASSIGN(
+      TokenizedDocument tokenized_document,
+      TokenizedDocument::Create(schema_store_.get(), lang_segmenter_.get(),
+                                document));
+
+  EXPECT_THAT(tokenized_document.document(), EqualsProto(document));
+  EXPECT_THAT(tokenized_document.num_string_tokens(), Eq(0));
+
+  // string sections
+  EXPECT_THAT(tokenized_document.tokenized_string_sections(), IsEmpty());
+
+  // integer sections
+  EXPECT_THAT(tokenized_document.integer_sections(), IsEmpty());
+
+  // Qualified id join properties
+  EXPECT_THAT(tokenized_document.qualified_id_join_properties(), SizeIs(2));
+  EXPECT_THAT(tokenized_document.qualified_id_join_properties().at(0).metadata,
+              Eq(kQualifiedId1JoinablePropertyMetadata));
+  EXPECT_THAT(tokenized_document.qualified_id_join_properties().at(0).values,
+              ElementsAre("pkg$db/ns#uri1"));
+  EXPECT_THAT(tokenized_document.qualified_id_join_properties().at(1).metadata,
+              Eq(kQualifiedId2JoinablePropertyMetadata));
+  EXPECT_THAT(tokenized_document.qualified_id_join_properties().at(1).values,
+              ElementsAre("pkg$db/ns#uri2"));
 }
 
 }  // namespace
diff --git a/proto/icing/index/numeric/wildcard-property-storage.proto b/proto/icing/index/numeric/wildcard-property-storage.proto
new file mode 100644
index 0000000..7f02b77
--- /dev/null
+++ b/proto/icing/index/numeric/wildcard-property-storage.proto
@@ -0,0 +1,22 @@
+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+syntax = "proto2";
+
+package icing.lib;
+
+// Next tag: 2
+message WildcardPropertyStorage {
+  repeated string property_entries = 1;
+}
diff --git a/proto/icing/proto/initialize.proto b/proto/icing/proto/initialize.proto
index 7fe1e6f..40a0d0c 100644
--- a/proto/icing/proto/initialize.proto
+++ b/proto/icing/proto/initialize.proto
@@ -23,7 +23,7 @@ option java_package = "com.google.android.icing.proto";
 option java_multiple_files = true;
 option objc_class_prefix = "ICNG";
 
-// Next tag: 5
+// Next tag: 7
 message IcingSearchEngineOptions {
   // Directory to persist files for Icing. Required.
   // If Icing was previously initialized with this directory, it will reload
@@ -58,6 +58,23 @@ message IcingSearchEngineOptions {
   // Optional.
   optional int32 index_merge_size = 4 [default = 1048576];  // 1 MiB
 
+  // Whether to use namespace id or namespace name to build up fingerprint for
+  // document_key_mapper_ and corpus_mapper_ in document store.
+  // TODO(b/259969017) Flip the default value of this flag to true at the time
+  // when we switch to use persistent hash map for document_key_mapper_ so that
+  // we just need one reconstruction of the internal mappers.
+  optional bool document_store_namespace_id_fingerprint = 5;
+
+  // The threshold of the percentage of invalid documents to rebuild index
+  // during optimize, i.e. we rebuild index if and only if
+  // |invalid_documents| / |all_documents| >= optimize_rebuild_index_threshold
+  //
+  // Rebuilding the index could be faster than optimizing the index if we have
+  // removed most of the documents.
+  // Based on benchmarks, 85%~95% seems to be a good threshold for most cases.
+  //
+  // Default to 0 for better rollout of the new index optimize.
+  optional float optimize_rebuild_index_threshold = 6 [default = 0.0];
   reserved 2;
 }
 
diff --git a/proto/icing/proto/logging.proto b/proto/icing/proto/logging.proto
index feb2643..edfcf40 100644
--- a/proto/icing/proto/logging.proto
+++ b/proto/icing/proto/logging.proto
@@ -23,7 +23,7 @@ option java_multiple_files = true;
 option objc_class_prefix = "ICNG";
 
 // Stats of the top-level function IcingSearchEngine::Initialize().
-// Next tag: 13
+// Next tag: 14
 message InitializeStatsProto {
   // Overall time used for the function call.
   optional int32 latency_ms = 1;
@@ -105,6 +105,12 @@ message InitializeStatsProto {
   // - SCHEMA_CHANGES_OUT_OF_SYNC
   // - IO_ERROR
   optional RecoveryCause integer_index_restoration_cause = 12;
+
+  // Possible recovery causes for qualified id join index:
+  // - INCONSISTENT_WITH_GROUND_TRUTH
+  // - SCHEMA_CHANGES_OUT_OF_SYNC
+  // - IO_ERROR
+  optional RecoveryCause qualified_id_join_index_restoration_cause = 13;
 }
 
 // Stats of the top-level function IcingSearchEngine::Put().
diff --git a/proto/icing/proto/search.proto b/proto/icing/proto/search.proto
index c9e2b1d..8bdbf0c 100644
--- a/proto/icing/proto/search.proto
+++ b/proto/icing/proto/search.proto
@@ -85,7 +85,8 @@ message SearchSpecProto {
   // enable testing.
   // TODO(b/208654892) Remove this field once EXPERIMENTAL_ICING_ADVANCED_QUERY
   // is fully supported.
-  optional SearchType.Code search_type = 6 [default = ICING_RAW_QUERY];
+  optional SearchType.Code search_type = 6
+      [default = EXPERIMENTAL_ICING_ADVANCED_QUERY];
 
   // OPTIONAL: If this field is present, join documents based on a nested
   // SearchSpec.
diff --git a/synced_AOSP_CL_number.txt b/synced_AOSP_CL_number.txt
index 232fbe0..5ff4997 100644
--- a/synced_AOSP_CL_number.txt
+++ b/synced_AOSP_CL_number.txt
@@ -1 +1 @@
-set(synced_AOSP_CL_number=-514555603)
+set(synced_AOSP_CL_number=516534290)