Package org.apache.lucene.codecs.lucene99

Class Lucene99HnswVectorsFormat

  • All Implemented Interfaces:
    NamedSPILoader.NamedSPI
    public final class Lucene99HnswVectorsFormat
extends KnnVectorsFormat
    Lucene 9.9 vector format, which encodes numeric vector values into an associated graph connecting the documents having values. The graph is used to power HNSW search. The format consists of two files, and requires a FlatVectorsFormat to store the actual vectors:

    .vex (vector index)

    Stores graphs connecting the documents for each field organized as a list of nodes' neighbours as following:

    • For each level:
      • For each node:
        • [vint] the number of neighbor nodes
        • array[vint] the delta encoded neighbor ordinals
    • After all levels are encoded memory offsets for each node's neighbor nodes encoded by DirectMonotonicWriter are appended to the end of the file.

    .vem (vector metadata) file

    For each field:

    • [int32] field number
    • [int32] vector similarity function ordinal
    • [vlong] offset to this field's index in the .vex file
    • [vlong] length of this field's index data, in bytes
    • [vint] dimension of this field's vectors
    • [int] the number of documents having values for this field
    • [int8] if equals to -1, dense – all documents have values for a field. If equals to 0, sparse – some documents missing values.
    • DocIds were encoded by IndexedDISI.writeBitSet(DocIdSetIterator, IndexOutput, byte)
    • OrdToDoc was encoded by DirectMonotonicWriter, note that only in sparse case
    • [vint] the maximum number of connections (neighbours) that each node can have
    • [vint] number of levels in the graph
    • Graph nodes by level. For each level
      • [vint] the number of nodes on this level
      • array[vint] for levels greater than 0 list of nodes on this level, stored as the level 0th delta encoded nodes' ordinals.
    WARNING: This API is experimental and might change in incompatible ways in the next release.

    • Field Detail

      • DEFAULT_MAX_CONN

        public static final int DEFAULT_MAX_CONN
        Default number of maximum connections per node
        See Also:
        Constant Field Values

      • DEFAULT_BEAM_WIDTH

        public static final int DEFAULT_BEAM_WIDTH
        Default number of the size of the queue maintained while searching during a graph construction.
        See Also:
        Constant Field Values

      • DEFAULT_NUM_MERGE_WORKER

        public static final int DEFAULT_NUM_MERGE_WORKER
        Default to use single thread merge
        See Also:
        Constant Field Values

    • Constructor Detail

      • Lucene99HnswVectorsFormat

        public Lucene99HnswVectorsFormat()
        Constructs a format using default graph construction parameters

      • Lucene99HnswVectorsFormat

        public Lucene99HnswVectorsFormat​(int maxConn,
                                 int beamWidth)
        Constructs a format using the given graph construction parameters.
        Parameters:
        maxConn - the maximum number of connections to a node in the HNSW graph
        beamWidth - the size of the queue maintained during graph construction.

      • Lucene99HnswVectorsFormat

        public Lucene99HnswVectorsFormat​(int maxConn,
                                 int beamWidth,
                                 int numMergeWorkers,
                                 ExecutorService mergeExec)
        Constructs a format using the given graph construction parameters and scalar quantization.
        Parameters:
        maxConn - the maximum number of connections to a node in the HNSW graph
        beamWidth - the size of the queue maintained during graph construction.
        numMergeWorkers - number of workers (threads) that will be used when doing merge. If larger than 1, a non-null ExecutorService must be passed as mergeExec
        mergeExec - the ExecutorService that will be used by ALL vector writers that are generated by this format to do the merge