FHybridSearchIndex

Singleton that owns all search indices (vector + BM25) and fuses results using Reciprocal Rank Fusion (RRF).

API > API/Plugins > API/Plugins/SemanticSearch

Singleton that owns all search indices (vector + BM25) and fuses results using Reciprocal Rank Fusion (RRF).

All mutations, searches, and index queries are serialized through an internal command queue with a dedicated consumer thread. Public methods enqueue work (microsecond lock) and return immediately; async operations deliver results via game-thread callbacks. GetCachedIndexStats() provides a lock-free snapshot of index metrics that is safe to call from any thread.

   
Name FHybridSearchIndex
Type class
Header File /Engine/Plugins/Experimental/SemanticSearch/Source/SemanticSearch/Public/HybridSearchIndex.h
Include Path #include "HybridSearchIndex.h"

Syntax

class FHybridSearchIndex

Constructors

Name Remarks Include Path Unreal Specifiers

FHybridSearchIndex()

   HybridSearchIndex.h  

Destructors

Name Remarks Include Path Unreal Specifiers

~FHybridSearchIndex()

   HybridSearchIndex.h  

Variables

Protected

Name Type Remarks Include Path Unreal Specifiers
bInitialized std::atomic< bool >   HybridSearchIndex.h  
BM25Index TUniquePtr< FBM25Index >   HybridSearchIndex.h  
FailedAssets TSet< int64 > Retryable failures. In-session only; cleared by the "Retry failed" button and on force-rebuild. HybridSearchIndex.h  
IndexId std::atomic< uint32 >   HybridSearchIndex.h  
OnIndexChangedDelegate FOnIndexChanged   HybridSearchIndex.h  
PreProcessorFailedAssets TSet< int64 > Permanent failures. HybridSearchIndex.h  
QueueData TUniquePtr< FCommandQueueData >   HybridSearchIndex.h  
VectorIndex TSharedPtr< IVectorIndex >   HybridSearchIndex.h  

Functions

Public

Name Remarks Include Path Unreal Specifiers

void Add ( FAssetData Asset,
TArray< float > Embedding,
FString Caption,
TArray< FString > Keywords,
uint32 IndexId
)

 Add a single asset to both indices. Lazily creates vector index on first call. HybridSearchIndex.h  

void AddQuantized ( FAssetData Asset,
TArray< uint8 > QuantizedCodes,
FString Caption,
TArray< FString > Keywords,
uint32 IndexId
)

 Add a single asset using pre-quantized codes (no float embedding). HybridSearchIndex.h  

void ClearBM25()

 Clear the BM25 text index. HybridSearchIndex.h  

void ClearFailedState ( int64 AssetId
)

 Remove an asset ID from both failed sets. Used by the retry button. HybridSearchIndex.h  

void ContainsAsync ( TArray< int64 > IDs,
TFunction< void(TSet< int64 >&&)> Callback
)

 Async contains check. Tests which IDs are present in the index on the consumer thread. HybridSearchIndex.h  

void DiscardPendingMutations()

 Discard all pending mutations (used during cancel). HybridSearchIndex.h  

void EnsureInitialized ( int32 EmbeddingDimension
)

 Ensure the index is initialized with a valid (possibly empty) vector index. HybridSearchIndex.h  

void ExtractEmbeddingsAsync ( TArray< int64 > CandidateIDs,
TFunction< void(TArray< int64 >&&IDs, TArray< float >&&Vectors, int32 Dimension)> Callback
)

 Async extraction of all stored vectors for training. Runs on the consumer thread. HybridSearchIndex.h  

FIoHash GetCachedCodebookHash()

 Get the codebook hash from cached stats. Returns default FIoHash if not quantized/trained. HybridSearchIndex.h  
Get a snapshot of index stats. HybridSearchIndex.h  

uint32 GetIndexId()

 Get the current index ID (changes on index swap/invalidation). HybridSearchIndex.h  

void InvalidateIndexId()

 Invalidate the current IndexId so stale callbacks are dropped. HybridSearchIndex.h  

void IsFailedAsync ( TArray< int64 > IDs,
TFunction< void(TSet< int64 >&&)> Callback
)

 Async failed-set check. HybridSearchIndex.h  

bool IsHybridEnabled()

 Whether BM25 hybrid search is enabled (from settings). HybridSearchIndex.h  

void IsRetryableFailedAsync ( TArray< int64 > IDs,
TFunction< void(TSet< int64 >&&)> Callback
)

 Async retryable-failed check. HybridSearchIndex.h  

bool LoadFromFile ( const FString& FilePath,
TMap< int64, FIoHash >& OutPackageHashes
)

 Load a previously saved index from a file. HybridSearchIndex.h  

void LoadPreProcessorFailedFromFile ( const FString& FilePath
)

 Load the pre-processor-failed ID list from a sidecar file. HybridSearchIndex.h  

void MarkFailed ( int64 AssetId,
EAssetIndexFailureReason Reason,
uint32 IndexId
)

 Record that an asset failed to index. HybridSearchIndex.h  

FOnIndexChanged & OnIndexChanged ()

 Delegate broadcast when the index changes (e.g. after switching type or retraining). HybridSearchIndex.h  

void PurgePreProcessorFailedNotIn ( TSet< int64 > ValidIDs
)

 Purge pre-processor-failed IDs that are not in the given set of currently-valid IDs. HybridSearchIndex.h  

void QuantizeAsync ( TArray< float > Embedding,
TFunction< void(TArray< uint8 >&&, bool bSuccess)> Callback
)

 Async quantize. HybridSearchIndex.h  

void Remove ( FAssetData Asset
)

 Remove a single asset from both indices. HybridSearchIndex.h  

void RemoveById ( int64 AssetId
)

 Remove by pre-computed ID. HybridSearchIndex.h  

void RemoveByPath ( FString AssetPath
)

 Remove by path string (for when the asset has already been deleted). HybridSearchIndex.h  
Reset BM25 and failed sets (enqueued to consumer thread). HybridSearchIndex.h  

void Save ( FString FilePath,
FString PreProcessorFailedPath,
TMap< int64, FIoHash > PackageHashes
)

 Save the full index (vector + BM25 + package hashes) to a file, and the pre-processor-failed ID list to a sidecar file alongside it. HybridSearchIndex.h  

void SearchAsync ( FString QueryText,
TArray< float > QueryEmbedding,
int32 K,
TArray< int64 > IDFilter,
float DistanceCutoff,
TFunction< void(TArray< FHybridSearchResult >&&)> Callback
)

 Async search. Fuses vector + BM25 results via RRF. HybridSearchIndex.h  

void SetVectorIndex ( TSharedPtr< IVectorIndex > NewIndex
)

 Replace the vector index. Used during index type switching. HybridSearchIndex.h  

void StartCommandQueue()

 Start the background consumer thread. HybridSearchIndex.h  

void StopCommandQueue()

 Stop the background consumer thread and join. HybridSearchIndex.h  

Static

Name Remarks Include Path Unreal Specifiers

static FHybridSearchIndex & Get()

   HybridSearchIndex.h  

static FString GetCodebookPath ( ESemanticSearchIndexType Type
)

 Get the path to the shared codebook file for the given index type (in plugin Resources/). HybridSearchIndex.h  

static void WriteBytesToFile ( const FString& FilePath,
TArray64< uint8 > Bytes
)

   HybridSearchIndex.h  

Ask questions and help your peers Developer Forums

Write your own tutorials or read those from others Learning Library

On this page