benwtrent commented on code in PR #15415: URL: https://github.com/apache/lucene/pull/15415#discussion_r2519362543
########## lucene/core/src/java/org/apache/lucene/codecs/lucene104/OffHeapScalarQuantizedFloatVectorValues.java: ########## @@ -0,0 +1,427 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. + * The ASF licenses this file to You 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. + */ + +package org.apache.lucene.codecs.lucene104; + +import static org.apache.lucene.util.quantization.OptimizedScalarQuantizer.deQuantize; + +import java.io.IOException; +import java.nio.ByteBuffer; +import org.apache.lucene.codecs.hnsw.FlatVectorsScorer; +import org.apache.lucene.codecs.lucene90.IndexedDISI; +import org.apache.lucene.codecs.lucene95.HasIndexSlice; +import org.apache.lucene.codecs.lucene95.OrdToDocDISIReaderConfiguration; +import org.apache.lucene.index.FloatVectorValues; +import org.apache.lucene.index.VectorSimilarityFunction; +import org.apache.lucene.search.DocIdSetIterator; +import org.apache.lucene.search.VectorScorer; +import org.apache.lucene.store.IndexInput; +import org.apache.lucene.util.Bits; +import org.apache.lucene.util.hnsw.RandomVectorScorer; +import org.apache.lucene.util.packed.DirectMonotonicReader; +import org.apache.lucene.util.quantization.OptimizedScalarQuantizer; + +/** + * Reads quantized vector values from the index input and returns float vector values after + * dequantizing them. + * + * <p>This class provides functionality to read quantized vectors which are stored in the index, and + * then dequantize them back to float vectors with some precision loss. The implementation is based + * on {@code OffHeapScalarQuantizedVectorValues} with modifications to the {@code vectorValue()} + * method to return float vectors after dequantizing the vectors. + * + * <p>Usage: This class is used for read-only indexes where full-precision float vectors have been + * dropped from the index to save storage space. Full-precision vectors can be removed from an index + * using a method as implemented in {@code + * TestLucene104ScalarQuantizedVectorsFormat.simulateEmptyRawVectors()}. + * + * @lucene.internal + */ +abstract class OffHeapScalarQuantizedFloatVectorValues extends FloatVectorValues + implements HasIndexSlice { + + final int dimension; + final int size; + final VectorSimilarityFunction similarityFunction; + final FlatVectorsScorer vectorsScorer; + + final IndexInput slice; + final float[] vectorValue; + final byte[] byteValue; + final ByteBuffer byteBuffer; + final byte[] unpackedByteVectorValue; + final int byteSize; + private int lastOrd = -1; + final float[] correctiveValues; + int quantizedComponentSum; + final Lucene104ScalarQuantizedVectorsFormat.ScalarEncoding encoding; + final float[] centroid; + final boolean isQuerySide; + + OffHeapScalarQuantizedFloatVectorValues( + int dimension, + int size, + float[] centroid, + Lucene104ScalarQuantizedVectorsFormat.ScalarEncoding encoding, + VectorSimilarityFunction similarityFunction, + FlatVectorsScorer vectorsScorer, + IndexInput slice) { + this(false, dimension, size, centroid, encoding, similarityFunction, vectorsScorer, slice); + } + + OffHeapScalarQuantizedFloatVectorValues( + boolean isQuerySide, Review Comment: We should never allow this "querySide" thing. Even as it is now, it wouldn't work. ########## lucene/CHANGES.txt: ########## @@ -176,6 +176,9 @@ New Features `Lucene104HnswScalarQuantizedVectorsFormat(ScalarEncoding.SINGLE_BIT_QUERY_NIBBLE, int, int)` (Ben Trent) + * GITHUB#15415: Add fallback support to Lucene104ScalarQuantizedVectorsFormat getFloatVectorValues when there are + no full-precision vectors present Review Comment: Please add your name for posterity :) ########## lucene/core/src/java/org/apache/lucene/codecs/lucene104/OffHeapScalarQuantizedFloatVectorValues.java: ########## @@ -0,0 +1,427 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. + * The ASF licenses this file to You 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. + */ + +package org.apache.lucene.codecs.lucene104; + +import static org.apache.lucene.util.quantization.OptimizedScalarQuantizer.deQuantize; + +import java.io.IOException; +import java.nio.ByteBuffer; +import org.apache.lucene.codecs.hnsw.FlatVectorsScorer; +import org.apache.lucene.codecs.lucene90.IndexedDISI; +import org.apache.lucene.codecs.lucene95.HasIndexSlice; +import org.apache.lucene.codecs.lucene95.OrdToDocDISIReaderConfiguration; +import org.apache.lucene.index.FloatVectorValues; +import org.apache.lucene.index.VectorSimilarityFunction; +import org.apache.lucene.search.DocIdSetIterator; +import org.apache.lucene.search.VectorScorer; +import org.apache.lucene.store.IndexInput; +import org.apache.lucene.util.Bits; +import org.apache.lucene.util.hnsw.RandomVectorScorer; +import org.apache.lucene.util.packed.DirectMonotonicReader; +import org.apache.lucene.util.quantization.OptimizedScalarQuantizer; + +/** + * Reads quantized vector values from the index input and returns float vector values after + * dequantizing them. + * + * <p>This class provides functionality to read quantized vectors which are stored in the index, and + * then dequantize them back to float vectors with some precision loss. The implementation is based + * on {@code OffHeapScalarQuantizedVectorValues} with modifications to the {@code vectorValue()} + * method to return float vectors after dequantizing the vectors. + * + * <p>Usage: This class is used for read-only indexes where full-precision float vectors have been + * dropped from the index to save storage space. Full-precision vectors can be removed from an index + * using a method as implemented in {@code + * TestLucene104ScalarQuantizedVectorsFormat.simulateEmptyRawVectors()}. + * + * @lucene.internal + */ +abstract class OffHeapScalarQuantizedFloatVectorValues extends FloatVectorValues + implements HasIndexSlice { + + final int dimension; + final int size; + final VectorSimilarityFunction similarityFunction; + final FlatVectorsScorer vectorsScorer; + + final IndexInput slice; + final float[] vectorValue; + final byte[] byteValue; + final ByteBuffer byteBuffer; + final byte[] unpackedByteVectorValue; + final int byteSize; + private int lastOrd = -1; + final float[] correctiveValues; + int quantizedComponentSum; + final Lucene104ScalarQuantizedVectorsFormat.ScalarEncoding encoding; + final float[] centroid; + final boolean isQuerySide; + + OffHeapScalarQuantizedFloatVectorValues( + int dimension, + int size, + float[] centroid, + Lucene104ScalarQuantizedVectorsFormat.ScalarEncoding encoding, + VectorSimilarityFunction similarityFunction, + FlatVectorsScorer vectorsScorer, + IndexInput slice) { + this(false, dimension, size, centroid, encoding, similarityFunction, vectorsScorer, slice); + } + + OffHeapScalarQuantizedFloatVectorValues( + boolean isQuerySide, + int dimension, + int size, + float[] centroid, + Lucene104ScalarQuantizedVectorsFormat.ScalarEncoding encoding, + VectorSimilarityFunction similarityFunction, + FlatVectorsScorer vectorsScorer, + IndexInput slice) { + assert isQuerySide == false || encoding.isAsymmetric(); + this.isQuerySide = isQuerySide; + this.dimension = dimension; + this.size = size; + this.similarityFunction = similarityFunction; + this.vectorsScorer = vectorsScorer; + this.slice = slice; + this.centroid = centroid; + this.correctiveValues = new float[3]; + this.encoding = encoding; + int docPackedLength = + isQuerySide + ? encoding.getQueryPackedLength(dimension) + : encoding.getDocPackedLength(dimension); + this.byteSize = docPackedLength + (Float.BYTES * 3) + Integer.BYTES; + this.byteBuffer = ByteBuffer.allocate(docPackedLength); + this.vectorValue = new float[dimension]; + this.byteValue = byteBuffer.array(); + this.unpackedByteVectorValue = new byte[dimension]; + } + + @Override + public int dimension() { + return dimension; + } + + @Override + public int size() { + return size; + } + + @Override + public float[] vectorValue(int targetOrd) throws IOException { + if (lastOrd == targetOrd) { + return vectorValue; + } + + // read quantized byte vector, correctiveValues and quantizedComponentSum + slice.seek((long) targetOrd * byteSize); + slice.readBytes(byteBuffer.array(), byteBuffer.arrayOffset(), byteValue.length); + slice.readFloats(correctiveValues, 0, 3); + quantizedComponentSum = slice.readInt(); + + // unpack bytes + switch (encoding) { + case PACKED_NIBBLE -> + OffHeapScalarQuantizedVectorValues.unpackNibbles(byteValue, unpackedByteVectorValue); + case SINGLE_BIT_QUERY_NIBBLE -> + OptimizedScalarQuantizer.unpackBinary(byteValue, unpackedByteVectorValue); + case UNSIGNED_BYTE, SEVEN_BIT -> { + deQuantize(byteValue, vectorValue, encoding.getBits(), correctiveValues, centroid); + lastOrd = targetOrd; + return vectorValue; + } + } Review Comment: If this was "query side" it wouldn't work. Consequently, I think this query side thing should go away. I think this piece is great if we always assume document quantized bits. ########## lucene/core/src/java/org/apache/lucene/util/quantization/OptimizedScalarQuantizer.java: ########## @@ -236,6 +236,37 @@ public QuantizationResult scalarQuantize( sumQuery); } + /** + * Dequantizes a quantized byte vector back to float values. + * + * <p>This method reconstructs float vectors from their quantized byte representation using linear + * interpolation between the corrective range [a, b] and adding back the centroid offset. + * + * @param quantized the quantized byte vector to dequantize + * @param dequantized the output array to store dequantized float values + * @param bits the number of bits used for quantization + * @param correctiveValues array containing [a, b, unused] where a=min, b=max of quantization + * range + * @param centroid the centroid vector that was subtracted during quantization + * @return the dequantized float array (same as dequantized parameter) + */ + public static float[] deQuantize( + byte[] quantized, + float[] dequantized, + byte bits, + float[] correctiveValues, Review Comment: maybe make this specifically `lower` `upper` thing instead of this array? -- This is an automated message from the Apache Git Service. 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