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Posted to issues@lucene.apache.org by GitBox <gi...@apache.org> on 2020/03/22 19:55:56 UTC
[GitHub] [lucene-solr] msokolov commented on a change in pull request #1316:
LUCENE-8929 parallel early termination in TopFieldCollector using minmin
score
msokolov commented on a change in pull request #1316: LUCENE-8929 parallel early termination in TopFieldCollector using minmin score
URL: https://github.com/apache/lucene-solr/pull/1316#discussion_r396134224
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File path: lucene/core/src/java/org/apache/lucene/search/ParallelSortedCollector.java
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@@ -0,0 +1,612 @@
+/*
+ * 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.Collection;
+import java.util.List;
+import java.util.PriorityQueue;
+
+import org.apache.lucene.index.LeafReaderContext;
+import org.apache.lucene.search.FieldValueHitQueue.Entry;
+import org.apache.lucene.search.TotalHits.Relation;
+
+/**
+ * A {@link Collector} for results sorted by field, optimized for early termination in
+ * the case where the {@link Sort} matches the index and the search is executed in parallel,
+ * using multiple threads.
+ *
+ * @lucene.experimental
+ */
+abstract class ParallelSortedCollector extends TopDocsCollector<Entry> {
+
+ private static final ScoreDoc[] EMPTY_SCOREDOCS = new ScoreDoc[0];
+
+ final int numHits;
+ final Sort sort;
+ final HitsThresholdChecker hitsThresholdChecker;
+ final FieldComparator<?> firstComparator;
+
+ // the current local minimum competitive score already propagated to the underlying scorer
+ float minCompetitiveScore;
+
+ // Enables global early termination with concurrent threads using minimum competitive scores and
+ // collected counts of all segments
+ final MaxScoreTerminator maxScoreTerminator;
+
+ final int numComparators;
+ FieldValueHitQueue.Entry bottom = null;
+ boolean queueFull;
+ int docBase;
+ final boolean needsScores;
+ final ScoreMode scoreMode;
+
+ // Declaring the constructor private prevents extending this class by anyone
+ // else. Note that the class cannot be final since it's extended by the
+ // internal versions. If someone will define a constructor with any other
+ // visibility, then anyone will be able to extend the class, which is not what
+ // we want.
+ private ParallelSortedCollector(FieldValueHitQueue<Entry> pq, int numHits, Sort sort,
+ HitsThresholdChecker hitsThresholdChecker, boolean needsScores,
+ MaxScoreTerminator maxScoreTerminator) {
+ super(pq);
+ this.needsScores = needsScores;
+ this.numHits = numHits;
+ this.sort = sort;
+ this.hitsThresholdChecker = hitsThresholdChecker;
+ this.maxScoreTerminator = maxScoreTerminator;
+ numComparators = pq.getComparators().length;
+ firstComparator = pq.getComparators()[0];
+ scoreMode = needsScores ? ScoreMode.COMPLETE : ScoreMode.COMPLETE_NO_SCORES;
+ }
+
+ private abstract class TopFieldLeafCollector implements LeafCollector {
+
+ final LeafFieldComparator comparator;
+ final int firstReverseMul;
+ final int reverseMul;
+ final LeafReaderContext context;
+ final MaxScoreTerminator.LeafState leafTerminationState;
+
+ private double score;
+ Scorable scorer;
+
+ TopFieldLeafCollector(FieldValueHitQueue<Entry> queue, LeafReaderContext context) throws IOException {
+ LeafFieldComparator[] comparators = queue.getComparators(context);
+ firstReverseMul = queue.reverseMul[0];
+ if (comparators.length == 1) {
+ this.reverseMul = queue.reverseMul[0];
+ this.comparator = comparators[0];
+ } else {
+ this.reverseMul = 1;
+ this.comparator = new MultiLeafFieldComparator(comparators, queue.reverseMul);
+ }
+ this.context = context;
+ leafTerminationState = maxScoreTerminator.addLeafState();
+ }
+
+ void countHit() {
+ ++totalHits;
+ // TODO: replace hitsThresholdChecker with something simpler
+ hitsThresholdChecker.incrementHitCount();
+ }
+
+ void collectHitIfCompetitive(int doc) throws IOException {
+ if (reverseMul * comparator.compareBottom(doc) > 0) {
+ comparator.copy(bottom.slot, doc);
+ score = getComparatorValue(bottom.slot);
+ //System.out.printf("leaf=%d doc=%d score=%f\n", context.ord, context.docBase + doc, score);
+ updateBottom(doc);
+ comparator.setBottom(bottom.slot);
+ } else {
+ // The comparator has no score from this document. We can use any noncompetitive value
+ // to induce this leaf to be terminated.
+ //System.out.printf("leaf=%d doc=%d (noncompetitive) score=%f\n", context.ord, context.docBase + doc, score);
+ score = getComparatorValue(bottom.slot) + 1;
+ }
+ }
+
+ void collectAnyHit(int doc, int hitsCollected) throws IOException {
+ // Startup transient: queue hasn't gathered numHits yet
+ int slot = hitsCollected - 1;
+ // Copy hit into queue
+ comparator.copy(slot, doc);
+ // compute the doc's score before it gets moved by updating the priority queue
+ score = getComparatorValue(slot);
+ add(slot, doc);
+ if (queueFull) {
+ comparator.setBottom(bottom.slot);
+ }
+ }
+
+ private double getComparatorValue(int slot) {
+ // We could avoid this cast by genericizing MaxScoreAccumulator and having its Number type
+ // co-vary with this FieldComparator; also - should DocComparator extend
+ // NumericComparator<Integer>?
+ return firstReverseMul * ((Number) firstComparator.value(slot)).doubleValue();
+ }
+
+ void updateTerminationState(int doc) {
+ leafTerminationState.update(score, context.docBase + doc);
+ if ((leafTerminationState.resultCount & maxScoreTerminator.intervalMask) == 0) {
+ //System.out.println("scoreboard update leaf=" + context.ord + " doc=" + context.docBase + "+" + doc + " total=" + totalHits);
+ if (maxScoreTerminator.updateLeafState(leafTerminationState)) {
+ // Stop if across all segments we have collected enough, and our scores are no longer competitive
+ totalHitsRelation = Relation.GREATER_THAN_OR_EQUAL_TO;
+ //System.out.println("scoreboard terminate leaf " + context.ord + " doc=" + context.docBase + "+" + doc + " totalHits=" + totalHits + " score=" + (long) score);
+ throw new CollectionTerminatedException();
+ }
+ }
+ }
+
+ @Override
+ public void setScorer(Scorable scorer) throws IOException {
+ this.scorer = scorer;
+ comparator.setScorer(scorer);
+ minCompetitiveScore = 0f;
+ }
+ }
+
+ static boolean isApplicable(Sort sort, int numHits, List<LeafReaderContext> leafContexts) {
+ for (LeafReaderContext leafContext : leafContexts) {
+ if (TopFieldCollector.canEarlyTerminate(sort, leafContext) == false) {
+ return false;
+ }
+ }
+ return MaxScoreTerminator.isApplicable(sort, numHits);
+ }
+
+ /*
+ * Implements a ParallelSortedCollector for the first page of results (after == null).
+ */
+ private static class TopCollector extends ParallelSortedCollector {
+ final FieldValueHitQueue<Entry> queue;
+
+ TopCollector(Sort sort, FieldValueHitQueue<Entry> queue, int numHits,
+ HitsThresholdChecker hitsThresholdChecker,
+ MaxScoreTerminator maxScoreTerminator) {
+ super(queue, numHits, sort, hitsThresholdChecker, sort.needsScores(), maxScoreTerminator);
+ this.queue = queue;
+ }
+
+ @Override
+ public LeafCollector getLeafCollector(LeafReaderContext context) throws IOException {
+ docBase = context.docBase;
+
+ return new TopFieldLeafCollector(queue, context) {
+
+ @Override
+ public void collect(int doc) throws IOException {
+ countHit();
+ if (queueFull) {
+ collectHitIfCompetitive(doc);
+ } else {
+ collectAnyHit(doc, totalHits);
+ }
+ updateTerminationState(doc);
+ }
+ };
+ }
+ }
+
+ /*
+ * Implements a ParallelSortedCollector when after != null.
+ */
+ private final static class PagingCollector extends ParallelSortedCollector {
+
+ int collectedHits;
+ final FieldValueHitQueue<Entry> queue;
+ final FieldDoc after;
+
+ PagingCollector(Sort sort, FieldValueHitQueue<Entry> queue, FieldDoc after, int numHits,
+ HitsThresholdChecker hitsThresholdChecker,
+ MaxScoreTerminator maxScoreTerminator) {
+ super(queue, numHits, sort, hitsThresholdChecker, sort.needsScores(), maxScoreTerminator);
+ this.queue = queue;
+ this.after = after;
+
+ FieldComparator<?>[] comparators = queue.comparators;
+ // Tell all comparators their top value:
+ for(int i=0; i<comparators.length; i++) {
+ @SuppressWarnings("unchecked")
+ FieldComparator<Object> comparator = (FieldComparator<Object>) comparators[i];
+ comparator.setTopValue(after.fields[i]);
+ }
+ }
+
+ @Override
+ public LeafCollector getLeafCollector(LeafReaderContext context) throws IOException {
+ docBase = context.docBase;
+ final int afterDoc = after.doc - docBase;
+
+ return new TopFieldLeafCollector(queue, context) {
+
+ @Override
+ public void collect(int doc) throws IOException {
+ countHit();
+ final int topCmp = reverseMul * comparator.compareTop(doc);
+ if (topCmp < 0 || (topCmp == 0 && doc > afterDoc)) {
+ if (queueFull) {
+ collectHitIfCompetitive(doc);
+ } else {
+ collectedHits++;
+ collectAnyHit(doc, collectedHits);
+ }
+ }
+ updateTerminationState(doc);
+ }
+ };
+ }
+ }
+
+ @Override
+ public ScoreMode scoreMode() {
+ return scoreMode;
+ }
+
+ /**
+ * Same as above with additional parameters to allow passing in the threshold checker and the max score accumulator.
+ */
+ static ParallelSortedCollector create(Sort sort, int numHits, FieldDoc after, HitsThresholdChecker hitsThresholdChecker,
+ MaxScoreTerminator maxScoreTerminator) {
+
+ if (sort.fields.length == 0) {
+ throw new IllegalArgumentException("Sort must contain at least one field");
+ }
+
+ if (numHits <= 0) {
+ throw new IllegalArgumentException("numHits must be > 0; please use TotalHitCountCollector if you just need the total hit count");
+ }
+
+ assert hitsThresholdChecker != null;
+ assert maxScoreTerminator != null;
+
+ FieldValueHitQueue<Entry> queue = FieldValueHitQueue.create(sort.fields, numHits);
+
+ if (after == null) {
+ return new TopCollector(sort, queue, numHits, hitsThresholdChecker, maxScoreTerminator);
+ } else {
+ if (after.fields == null) {
+ throw new IllegalArgumentException("after.fields wasn't set; you must pass fillFields=true for the previous search");
+ }
+
+ if (after.fields.length != sort.getSort().length) {
+ throw new IllegalArgumentException("after.fields has " + after.fields.length + " values but sort has " + sort.getSort().length);
+ }
+
+ return new PagingCollector(sort, queue, after, numHits, hitsThresholdChecker, maxScoreTerminator);
+ }
+ }
+
+ /**
+ * Create a CollectorManager which uses a shared hit counter to maintain number of hits, a shared {@link
+ * MaxScoreAccumulator} to propagate the minimum score across segments if the primary sort is by relevancy, and a
+ * shared {@link MaxScoreTerminator} that maintains per-collector statistics to facilitate early termination when
+ * primary sort matches the index sort.
+ * @param sort the criteria to sort results by; must be based on numeric fields and a prefix of the index sort
+ * @param numHits how many hits to collect
+ * @param after the position after which to start collecting hits, or null to collect starting with the first
+ * @param totalHitsThreshold a minimum number of hits to count
+ * @param numThreads how many threads will collect hits. Setting the wrong value will still
+ * collect hits correctly, but may compromise performance due to thread contention (if too small),
+ * or less-than-optimal early termination, if too large.
+ */
+ public static CollectorManager<ParallelSortedCollector, TopFieldDocs> createManager(Sort sort, int numHits, FieldDoc after,
+ int totalHitsThreshold, Integer numThreads) {
+ return new CollectorManager<>() {
+
+ private final HitsThresholdChecker hitsThresholdChecker = HitsThresholdChecker.createShared(totalHitsThreshold);
+ private final MaxScoreTerminator maxScoreTerminator = new MaxScoreTerminator(numHits, totalHitsThreshold, numThreads);
+
+ @Override
+ public ParallelSortedCollector newCollector() {
+ return create(sort, numHits, after, hitsThresholdChecker, maxScoreTerminator);
+ }
+
+ @Override
+ public TopFieldDocs reduce(Collection<ParallelSortedCollector> collectors) {
+ final TopFieldDocs[] topDocs = new TopFieldDocs[collectors.size()];
+ int i = 0;
+ for (ParallelSortedCollector collector : collectors) {
+ topDocs[i++] = collector.topDocs();
+ }
+ return TopDocs.merge(sort, 0, numHits, topDocs);
+ }
+ };
+ }
+
+ private void add(int slot, int doc) {
+ bottom = pq.add(new Entry(slot, docBase + doc));
+ // The queue is full either when totalHits == numHits (in SimpleFieldCollector), in which case
+ // slot = totalHits - 1, or when hitsCollected == numHits (in PagingFieldCollector this is hits
+ // on the current page) and slot = hitsCollected - 1.
+ assert slot < numHits;
+ queueFull = slot == numHits - 1;
+ }
+
+ private void updateBottom(int doc) {
+ // bottom.score is already set to Float.NaN in add().
+ bottom.doc = docBase + doc;
+ bottom = pq.updateTop();
+ }
+
+ /*
+ * Only the following callback methods need to be overridden since
+ * topDocs(int, int) calls them to return the results.
+ */
+ @Override
+ protected void populateResults(ScoreDoc[] results, int howMany) {
+ // avoid casting if unnecessary.
+ FieldValueHitQueue<Entry> queue = (FieldValueHitQueue<Entry>) pq;
+ for (int i = howMany - 1; i >= 0; i--) {
+ results[i] = queue.fillFields(queue.pop());
+ }
+ }
+
+ @Override
+ protected TopDocs newTopDocs(ScoreDoc[] results, int start) {
+ if (results == null) {
+ results = EMPTY_SCOREDOCS;
+ }
+
+ // If this is a maxScoring tracking collector and there were no results,
+ return new TopFieldDocs(new TotalHits(totalHits, totalHitsRelation), results, ((FieldValueHitQueue<Entry>) pq).getFields());
+ }
+
+ @Override
+ public TopFieldDocs topDocs() {
+ return (TopFieldDocs) super.topDocs();
+ }
+
+ /**
+ * <p>MaxScoreTerminator is used by TopFieldCollector when the query sort is a prefix of the index sort (in which case
+ * we can apply early termination), multiple threads are used for collection, and <code>numHits</code> is relatively
+ * high. It is notified periodically by leaf collectors calling {@link #updateLeafState} with their worst (ie maximum)
+ * score and how many hits they have collected. When enough hits are collected, MaxScoreTerminator notifies
+ * noncompetitive leaf collectors when they can stop (early terminate) by returning true from {@link
+ * #updateLeafState}.</p>
+ *
+ * <p>Used by TopFieldCollector to orchestrate early termination (when query sort matches index sort) based on the worst
+ * competitive score across all leaf collectors. Once we have globally collected the number of hits required to satisfy
+ * the query (<code>collectionThreshold</code>, below, typically <code>max(numHits, 1000)</code>) then the worst
+ * collected score across threads is a global lower bound on the score that must be met by any hit (we already have
+ * sufficient hits to satisfy the query with score better than that, so any later hit with a worse score will be
+ * discarded, and any Collector retrieving such a hit can be terminated). Further, once a collector terminates, the same
+ * logic applies to the remaining collectors, which can result in raising the bound further. The termination bound used
+ * is the minimum minimum score among the top collectors (ranked by their minimum scores) that together have at least
+ * <code>collectionThreshold</code> hits.</p>
+ *
+ * <p>MaxScoreTerminator implements this termination strategy by tracking the worst score, and number of hits collected,
+ * of each LeafCollector in {@link LeafState} objects that are shared with the leaf collectors, and updated by the
+ * collectors asynchronously. The leaf collectors check in periodically (every {@link #interval}th hit collected), at
+ * which time the leaf states are sorted, the termination bound is updated, and the collector is notified whether it can
+ * terminate. The interval must be a power of 2 (since a mask is used to check the period), and should be set as low as
+ * possible while avoiding thread contention on this synchronized method. A good heuristic seems to be the least power
+ * of 2 greater than than the number of threads in use.</p>
+ */
+ static class MaxScoreTerminator {
+
+ // This strategy performs best for higher N. The threshold below was determined empirically. The best tradeoff is
+ // probably related to number of threads used by the searcher and the overall counting threshold.
+ private static final int TERMINATION_STRATEGY_HIT_THRESHOLD = 50;
+
+ // By default we use 2^5-1 to check the remainder with a bitwise operation, but for best performance
+ // the actual value should always be set by calling setIntervalBits()
+ private static final int DEFAULT_INTERVAL_BITS = 5;
+ private int intervalMask;
+ int interval;
+
+ /** The worst score for each leaf */
+ private final List<LeafState> leafStates = new ArrayList<>();
+ private final List<LeafState> scratch = new ArrayList<>();
+
+ /** How many hits were requested: Collector's numHits. */
+ private final int numHits;
+
+ /** the worst hit over all */
+ private final LeafState thresholdState;
+
+ /** The total number of docs to collect: the max of the Collector's numHits and its early termination threshold. */
+ final int totalToCollect;
+
+ /** An upper bound on the number of docs "excluded" from max-score accounting due to early termination. */
+ private int numExcludedBound;
+
+ /** A lower bound on the total hits collected by all leaves */
+ private volatile int totalCollected;
+
+ /**
+ * @param numHits the number of hits to be returned
+ * @param collectionThreshold collect at least this many, even if numHits is less, for the sake of counting
+ * @param numThreads the number of threads that will be updating this concurrently. Controls the update interval.
+ * If null, an internal default is used.
+ */
+ MaxScoreTerminator(int numHits, int collectionThreshold, Integer numThreads) {
+ this.numHits = numHits;
+ this.totalToCollect = Math.max(numHits, collectionThreshold);
+ thresholdState = new LeafState();
+ thresholdState.score = Double.MAX_VALUE;
+ thresholdState.docid = Integer.MAX_VALUE;
+ if (numThreads != null) {
+ int numThreadsLog2 = 31 - Integer.numberOfLeadingZeros(numThreads);
+ setIntervalBits(numThreadsLog2 + 1);
+ } else {
+ setIntervalBits(DEFAULT_INTERVAL_BITS);
+ }
+ }
+
+ /**
+ * @param sort the query sort
+ * @param numHits the number of hits requested
+ * @return whether the Sort is compatible with early termination using {@link MaxScoreTerminator} and the number of hits
+ * requested is large enough to make this optimization likely to help.
+ */
+ static boolean isApplicable(Sort sort, int numHits) {
+ return numHits > TERMINATION_STRATEGY_HIT_THRESHOLD && sortIsNumeric(sort);
Review comment:
Oh I like it!
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