jpountz commented on a change in pull request #754: LUCENE-8875: Introduce Optimized Collector For Large Number Of Hits URL: https://github.com/apache/lucene-solr/pull/754#discussion_r300999896
########## File path: lucene/sandbox/src/java/org/apache/lucene/search/LargeNumHitsTopDocsCollector.java ########## @@ -0,0 +1,177 @@ +/* + * 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.search; + +import java.io.IOException; +import java.util.ArrayList; +import java.util.Collections; +import java.util.Comparator; +import java.util.List; + +import org.apache.lucene.index.LeafReaderContext; + +import static org.apache.lucene.search.TopDocsCollector.EMPTY_TOPDOCS; + +/** + * Optimized collector for large number of hits. + * The collector maintains an ArrayList of hits until it accumulates + * the requested number of hits. Post that, it builds a Priority Queue + * and starts filtering further hits based on the minimum competitive + * score. + */ +public class LargeNumHitsTopDocsCollector implements Collector { + private final List<ScoreDoc> hits = new ArrayList<>(); + private final int numHits; + HitQueue pq; + ScoreDoc pqTop; + int totalHits; + /** Whether {@link #totalHits} is exact or a lower bound. */ + protected TotalHits.Relation totalHitsRelation = TotalHits.Relation.EQUAL_TO; + + public LargeNumHitsTopDocsCollector(int numHits) { + this.numHits = numHits; + this.totalHits = 0; + } + + // We always return COMPLETE since this collector should ideally + // be used only with large number of hits case + @Override + public ScoreMode scoreMode() { + return ScoreMode.COMPLETE; + } + + @Override + public LeafCollector getLeafCollector(LeafReaderContext context) { + final int docBase = context.docBase; + return new TopScoreDocCollector.ScorerLeafCollector() { + + @Override + public void setScorer(Scorable scorer) throws IOException { + super.setScorer(scorer); + updateMinCompetitiveScore(scorer); + } + + @Override + public void collect(int doc) throws IOException { + float score = scorer.score(); + + // This collector relies on the fact that scorers produce positive values: + assert score >= 0; // NOTE: false for NaN + + if (totalHits < numHits) { + hits.add(new ScoreDoc(doc, score)); + totalHits++; + return; + } else if (totalHits == numHits) { + // Convert the list to a priority queue + + // We should get here only when priority queue + // has been built + assert pq == null; + assert pqTop == null; + pq = new HitQueue(numHits, false); + + for (int i = 0; i < hits.size(); i++) { + pq.add(hits.get(i)); + } + + pqTop = pq.top(); + } + + if (score > pqTop.score) { + pqTop.doc = doc + docBase; + pqTop.score = score; + pqTop = pq.updateTop(); + updateMinCompetitiveScore(scorer); + } + ++totalHits; + } + }; + } + + protected void updateMinCompetitiveScore(Scorable scorer) throws IOException { + if (pqTop != null) { + scorer.setMinCompetitiveScore(Math.nextUp(pqTop.score)); + } + totalHitsRelation = TotalHits.Relation.GREATER_THAN_OR_EQUAL_TO; + } + + public TopDocs topDocs(int howMany) { + + if (howMany <= 0 || howMany > totalHits) { + throw new IllegalArgumentException("Incorrect number of hits requested"); + } + + ScoreDoc[] results = new ScoreDoc[howMany]; + + // Get the requested results from either hits list or PQ + populateResults(results, howMany); + + return newTopDocs(results); + } + + /** + * Populates the results array with the ScoreDoc instances. This can be + * overridden in case a different ScoreDoc type should be returned. + */ + protected void populateResults(ScoreDoc[] results, int howMany) { + if (pq != null) { + assert totalHits >= numHits; + for (int i = howMany - 1; i >= 0; i--) { + results[i] = pq.pop(); + } + return; + } + + // Total number of hits collected were less than numHits + assert totalHits < numHits; + Collections.sort(hits, new Comparator<ScoreDoc>() { + @Override + public int compare(ScoreDoc o1, ScoreDoc o2) { + if (o1.score < o2.score) { + return -1; + } + else if (o1.score > o2.score) { + return 1; + } + + assert o1.doc != o2.doc; + + return o1.doc > o2.doc ? 1 : -1; + } + }); Review comment: `Comparator.comparing(scoreDoc -> scoreDoc.score).reversed().thenComparing(scoreDoc -> scoreDoc.doc)`? ---------------------------------------------------------------- This is an automated message from the Apache Git Service. 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