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Elasticsearch subproject :server
/*
* Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
* or more contributor license agreements. Licensed under the Elastic License
* 2.0 and the Server Side Public License, v 1; you may not use this file except
* in compliance with, at your election, the Elastic License 2.0 or the Server
* Side Public License, v 1.
*/
package org.elasticsearch.search.rescore;
import org.apache.lucene.search.Explanation;
import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.search.Query;
import org.apache.lucene.search.ScoreDoc;
import org.apache.lucene.search.TopDocs;
import java.io.IOException;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.Set;
import static java.util.stream.Collectors.toSet;
public final class QueryRescorer implements Rescorer {
public static final Rescorer INSTANCE = new QueryRescorer();
@Override
public TopDocs rescore(TopDocs topDocs, IndexSearcher searcher, RescoreContext rescoreContext) throws IOException {
assert rescoreContext != null;
if (topDocs == null || topDocs.scoreDocs.length == 0) {
return topDocs;
}
final QueryRescoreContext rescore = (QueryRescoreContext) rescoreContext;
org.apache.lucene.search.Rescorer rescorer = new org.apache.lucene.search.QueryRescorer(rescore.query()) {
@Override
protected float combine(float firstPassScore, boolean secondPassMatches, float secondPassScore) {
if (secondPassMatches) {
return rescore.scoreMode.combine(
firstPassScore * rescore.queryWeight(),
secondPassScore * rescore.rescoreQueryWeight()
);
}
// TODO: shouldn't this be up to the ScoreMode? I.e., we should just invoke ScoreMode.combine, passing 0.0f for the
// secondary score?
return firstPassScore * rescore.queryWeight();
}
};
// First take top slice of incoming docs, to be rescored:
TopDocs topNFirstPass = topN(topDocs, rescoreContext.getWindowSize());
// Save doc IDs for which rescoring was applied to be used in score explanation
Set topNDocIDs = Collections.unmodifiableSet(
Arrays.stream(topNFirstPass.scoreDocs).map(scoreDoc -> scoreDoc.doc).collect(toSet())
);
rescoreContext.setRescoredDocs(topNDocIDs);
// Rescore them:
TopDocs rescored = rescorer.rescore(searcher, topNFirstPass, rescoreContext.getWindowSize());
// Splice back to non-topN hits and resort all of them:
return combine(topDocs, rescored, (QueryRescoreContext) rescoreContext);
}
@Override
public Explanation explain(int topLevelDocId, IndexSearcher searcher, RescoreContext rescoreContext, Explanation sourceExplanation)
throws IOException {
if (sourceExplanation == null) {
// this should not happen but just in case
return Explanation.noMatch("nothing matched");
}
QueryRescoreContext rescore = (QueryRescoreContext) rescoreContext;
float primaryWeight = rescore.queryWeight();
Explanation prim;
if (sourceExplanation.isMatch()) {
prim = Explanation.match(
sourceExplanation.getValue().floatValue() * primaryWeight,
"product of:",
sourceExplanation,
Explanation.match(primaryWeight, "primaryWeight")
);
} else {
prim = Explanation.noMatch("First pass did not match", sourceExplanation);
}
if (rescoreContext.isRescored(topLevelDocId)) {
Explanation rescoreExplain = searcher.explain(rescore.query(), topLevelDocId);
// NOTE: we don't use Lucene's Rescorer.explain because we want to insert our own description with which ScoreMode was used.
// Maybe we should add QueryRescorer.explainCombine to Lucene?
if (rescoreExplain != null && rescoreExplain.isMatch()) {
float secondaryWeight = rescore.rescoreQueryWeight();
Explanation sec = Explanation.match(
rescoreExplain.getValue().floatValue() * secondaryWeight,
"product of:",
rescoreExplain,
Explanation.match(secondaryWeight, "secondaryWeight")
);
QueryRescoreMode scoreMode = rescore.scoreMode();
return Explanation.match(
scoreMode.combine(prim.getValue().floatValue(), sec.getValue().floatValue()),
scoreMode + " of:",
prim,
sec
);
}
}
return prim;
}
private static final Comparator SCORE_DOC_COMPARATOR = (o1, o2) -> {
int cmp = Float.compare(o2.score, o1.score);
return cmp == 0 ? Integer.compare(o1.doc, o2.doc) : cmp;
};
/** Returns a new {@link TopDocs} with the topN from the incoming one, or the same TopDocs if the number of hits is already <=
* topN. */
private static TopDocs topN(TopDocs in, int topN) {
if (in.scoreDocs.length < topN) {
return in;
}
ScoreDoc[] subset = new ScoreDoc[topN];
System.arraycopy(in.scoreDocs, 0, subset, 0, topN);
return new TopDocs(in.totalHits, subset);
}
/** Modifies incoming TopDocs (in) by replacing the top hits with resorted's hits, and then resorting all hits. */
private static TopDocs combine(TopDocs in, TopDocs resorted, QueryRescoreContext ctx) {
System.arraycopy(resorted.scoreDocs, 0, in.scoreDocs, 0, resorted.scoreDocs.length);
if (in.scoreDocs.length > resorted.scoreDocs.length) {
// These hits were not rescored (beyond the rescore window), so we treat them the same as a hit that did get rescored but did
// not match the 2nd pass query:
for (int i = resorted.scoreDocs.length; i < in.scoreDocs.length; i++) {
// TODO: shouldn't this be up to the ScoreMode? I.e., we should just invoke ScoreMode.combine, passing 0.0f for the
// secondary score?
in.scoreDocs[i].score *= ctx.queryWeight();
}
// TODO: this is wrong, i.e. we are comparing apples and oranges at this point. It would be better if we always rescored all
// incoming first pass hits, instead of allowing recoring of just the top subset:
Arrays.sort(in.scoreDocs, SCORE_DOC_COMPARATOR);
}
return in;
}
public static class QueryRescoreContext extends RescoreContext {
private Query query;
private float queryWeight = 1.0f;
private float rescoreQueryWeight = 1.0f;
private QueryRescoreMode scoreMode;
public QueryRescoreContext(int windowSize) {
super(windowSize, QueryRescorer.INSTANCE);
this.scoreMode = QueryRescoreMode.Total;
}
public void setQuery(Query query) {
this.query = query;
}
@Override
public List getQueries() {
return Collections.singletonList(query);
}
public Query query() {
return query;
}
public float queryWeight() {
return queryWeight;
}
public float rescoreQueryWeight() {
return rescoreQueryWeight;
}
public QueryRescoreMode scoreMode() {
return scoreMode;
}
public void setRescoreQueryWeight(float rescoreQueryWeight) {
this.rescoreQueryWeight = rescoreQueryWeight;
}
public void setQueryWeight(float queryWeight) {
this.queryWeight = queryWeight;
}
public void setScoreMode(QueryRescoreMode scoreMode) {
this.scoreMode = scoreMode;
}
public void setScoreMode(String scoreMode) {
setScoreMode(QueryRescoreMode.fromString(scoreMode));
}
}
}