Remove LeafSimScorer abstraction. (#13957)

`LeafSimScorer` is a specialization of a `SimScorer` for a given segment. It
doesn't add much value, but benchmarks suggest that it adds measurable overhead
to queries sorted by score.

Author: jpountz

lucene/CHANGES.txt

@@ -9,6 +9,9 @@ API Changes
 ---------------------
 * GITHUB#11023: Removing deprecated parameters from CheckIndex. (Jakub Slowinski)
 
+* GITHUB#13957: Removed LeafSimScorer class, to save its overhead. Scorers now
+  compute scores directly from a SimScorer, postings and norms. (Adrien Grand)
+
 New Features
 ---------------------
 (No changes)

lucene/core/src/java/org/apache/lucene/document/FeatureQuery.java

@@ -27,7 +27,6 @@
 import org.apache.lucene.index.TermsEnum;
 import org.apache.lucene.search.Explanation;
 import org.apache.lucene.search.IndexSearcher;
-import org.apache.lucene.search.LeafSimScorer;
 import org.apache.lucene.search.Query;
 import org.apache.lucene.search.QueryVisitor;
 import org.apache.lucene.search.ScoreMode;
@@ -120,7 +119,6 @@ public Explanation explain(LeafReaderContext context, int doc) throws IOExceptio
 
       @Override
       public ScorerSupplier scorerSupplier(LeafReaderContext context) throws IOException {
-        final Weight thisWeight = this;
         Terms terms = Terms.getTerms(context.reader(), fieldName);
         TermsEnum termsEnum = terms.iterator();
         if (termsEnum.seekExact(new BytesRef(featureName)) == false) {
@@ -135,10 +133,8 @@ public ScorerSupplier scorerSupplier(LeafReaderContext context) throws IOExcepti
           @Override
           public Scorer get(long leadCost) throws IOException {
             final SimScorer scorer = function.scorer(boost);
-            final LeafSimScorer simScorer =
-                new LeafSimScorer(scorer, context.reader(), fieldName, false);
             final ImpactsEnum impacts = termsEnum.impacts(PostingsEnum.FREQS);
-            return new TermScorer(thisWeight, impacts, simScorer, topLevelScoringClause);
+            return new TermScorer(impacts, scorer, null, topLevelScoringClause);
           }
 
           @Override

lucene/core/src/java/org/apache/lucene/search/LeafSimScorer.java

@@ -18,6 +18,8 @@
 package org.apache.lucene.search;
 
 import java.io.IOException;
+import org.apache.lucene.index.NumericDocValues;
+import org.apache.lucene.search.similarities.Similarity.SimScorer;
 
 class PhraseScorer extends Scorer {
 
@@ -26,16 +28,19 @@ class PhraseScorer extends Scorer {
   final MaxScoreCache maxScoreCache;
   final PhraseMatcher matcher;
   final ScoreMode scoreMode;
-  private final LeafSimScorer simScorer;
+  private final SimScorer simScorer;
+  private final NumericDocValues norms;
   final float matchCost;
 
   private float minCompetitiveScore = 0;
   private float freq = 0;
 
-  PhraseScorer(PhraseMatcher matcher, ScoreMode scoreMode, LeafSimScorer simScorer) {
+  PhraseScorer(
+      PhraseMatcher matcher, ScoreMode scoreMode, SimScorer simScorer, NumericDocValues norms) {
     this.matcher = matcher;
     this.scoreMode = scoreMode;
     this.simScorer = simScorer;
+    this.norms = norms;
     this.matchCost = matcher.getMatchCost();
     this.approximation = matcher.approximation();
     this.impactsApproximation = matcher.impactsApproximation();
@@ -50,7 +55,11 @@ public boolean matches() throws IOException {
         matcher.reset();
         if (scoreMode == ScoreMode.TOP_SCORES && minCompetitiveScore > 0) {
           float maxFreq = matcher.maxFreq();
-          if (simScorer.score(docID(), maxFreq) < minCompetitiveScore) {
+          long norm = 1L;
+          if (norms != null && norms.advanceExact(docID())) {
+            norm = norms.longValue();
+          }
+          if (simScorer.score(maxFreq, norm) < minCompetitiveScore) {
             // The maximum score we could get is less than the min competitive score
             return false;
           }
@@ -79,7 +88,11 @@ public float score() throws IOException {
         freq += matcher.sloppyWeight();
       }
     }
-    return simScorer.score(docID(), freq);
+    long norm = 1L;
+    if (norms != null && norms.advanceExact(docID())) {
+      norm = norms.longValue();
+    }
+    return simScorer.score(freq, norm);
   }
 
   @Override

lucene/core/src/java/org/apache/lucene/search/PhraseScorer.java

@@ -19,6 +19,7 @@
 
 import java.io.IOException;
 import org.apache.lucene.index.LeafReaderContext;
+import org.apache.lucene.index.NumericDocValues;
 import org.apache.lucene.search.similarities.Similarity;
 import org.apache.lucene.search.similarities.Similarity.SimScorer;
 
@@ -63,9 +64,8 @@ protected abstract PhraseMatcher getPhraseMatcher(
   public ScorerSupplier scorerSupplier(LeafReaderContext context) throws IOException {
     PhraseMatcher matcher = getPhraseMatcher(context, stats, false);
     if (matcher == null) return null;
-    LeafSimScorer simScorer =
-        new LeafSimScorer(stats, context.reader(), field, scoreMode.needsScores());
-    final var scorer = new PhraseScorer(matcher, scoreMode, simScorer);
+    NumericDocValues norms = scoreMode.needsScores() ? context.reader().getNormValues(field) : null;
+    final var scorer = new PhraseScorer(matcher, scoreMode, stats, norms);
     return new DefaultScorerSupplier(scorer);
   }
 
@@ -83,10 +83,13 @@ public Explanation explain(LeafReaderContext context, int doc) throws IOExceptio
     while (matcher.nextMatch()) {
       freq += matcher.sloppyWeight();
     }
-    LeafSimScorer docScorer =
-        new LeafSimScorer(stats, context.reader(), field, scoreMode.needsScores());
     Explanation freqExplanation = Explanation.match(freq, "phraseFreq=" + freq);
-    Explanation scoreExplanation = docScorer.explain(doc, freqExplanation);
+    NumericDocValues norms = scoreMode.needsScores() ? context.reader().getNormValues(field) : null;
+    long norm = 1L;
+    if (norms != null && norms.advanceExact(doc)) {
+      norm = norms.longValue();
+    }
+    Explanation scoreExplanation = stats.explain(freqExplanation, norm);
     return Explanation.match(
         scoreExplanation.getValue(),
         "weight("

lucene/core/src/java/org/apache/lucene/search/PhraseWeight.java

@@ -30,6 +30,7 @@
 import org.apache.lucene.index.ImpactsEnum;
 import org.apache.lucene.index.ImpactsSource;
 import org.apache.lucene.index.LeafReaderContext;
+import org.apache.lucene.index.NumericDocValues;
 import org.apache.lucene.index.PostingsEnum;
 import org.apache.lucene.index.SlowImpactsEnum;
 import org.apache.lucene.index.Term;
@@ -38,6 +39,7 @@
 import org.apache.lucene.index.Terms;
 import org.apache.lucene.index.TermsEnum;
 import org.apache.lucene.search.similarities.Similarity;
+import org.apache.lucene.search.similarities.Similarity.SimScorer;
 import org.apache.lucene.util.BytesRef;
 import org.apache.lucene.util.IOSupplier;
 import org.apache.lucene.util.PriorityQueue;
@@ -259,9 +261,13 @@ public Explanation explain(LeafReaderContext context, int doc) throws IOExceptio
             assert scorer instanceof TermScorer;
             freq = ((TermScorer) scorer).freq();
           }
-          LeafSimScorer docScorer = new LeafSimScorer(simWeight, context.reader(), field, true);
           Explanation freqExplanation = Explanation.match(freq, "termFreq=" + freq);
-          Explanation scoreExplanation = docScorer.explain(doc, freqExplanation);
+          NumericDocValues norms = context.reader().getNormValues(field);
+          long norm = 1L;
+          if (norms != null && norms.advanceExact(doc)) {
+            norm = norms.longValue();
+          }
+          Explanation scoreExplanation = simWeight.explain(freqExplanation, norm);
           return Explanation.match(
               scoreExplanation.getValue(),
               "weight("
@@ -334,27 +340,27 @@ public Scorer get(long leadCost) throws IOException {
             return new ConstantScoreScorer(0f, scoreMode, DocIdSetIterator.empty());
           }
 
-          LeafSimScorer simScorer = new LeafSimScorer(simWeight, context.reader(), field, true);
+          NumericDocValues norms = context.reader().getNormValues(field);
 
           // we must optimize this case (term not in segment), disjunctions require >= 2 subs
           if (iterators.size() == 1) {
             final TermScorer scorer;
             if (scoreMode == ScoreMode.TOP_SCORES) {
-              scorer = new TermScorer(impacts.get(0), simScorer);
+              scorer = new TermScorer(impacts.get(0), simWeight, norms);
             } else {
-              scorer = new TermScorer(iterators.get(0), simScorer);
+              scorer = new TermScorer(iterators.get(0), simWeight, norms);
             }
             float boost = termBoosts.get(0);
             return scoreMode == ScoreMode.COMPLETE_NO_SCORES || boost == 1f
                 ? scorer
-                : new FreqBoostTermScorer(boost, scorer, simScorer);
+                : new FreqBoostTermScorer(boost, scorer, simWeight, norms);
           } else {
 
             // we use termscorers + disjunction as an impl detail
             DisiPriorityQueue queue = new DisiPriorityQueue(iterators.size());
             for (int i = 0; i < iterators.size(); i++) {
               PostingsEnum postings = iterators.get(i);
-              final TermScorer termScorer = new TermScorer(postings, simScorer);
+              final TermScorer termScorer = new TermScorer(postings, simWeight, norms);
               float boost = termBoosts.get(i);
               final DisiWrapperFreq wrapper = new DisiWrapperFreq(termScorer, boost);
               queue.add(wrapper);
@@ -368,8 +374,7 @@ public Scorer get(long leadCost) throws IOException {
               boosts[i] = termBoosts.get(i);
             }
             ImpactsSource impactsSource = mergeImpacts(impacts.toArray(new ImpactsEnum[0]), boosts);
-            MaxScoreCache maxScoreCache =
-                new MaxScoreCache(impactsSource, simScorer.getSimScorer());
+            MaxScoreCache maxScoreCache = new MaxScoreCache(impactsSource, simWeight);
             ImpactsDISI impactsDisi = new ImpactsDISI(iterator, maxScoreCache);
 
             if (scoreMode == ScoreMode.TOP_SCORES) {
@@ -379,7 +384,7 @@ public Scorer get(long leadCost) throws IOException {
               iterator = impactsDisi;
             }
 
-            return new SynonymScorer(queue, iterator, impactsDisi, simScorer);
+            return new SynonymScorer(queue, iterator, impactsDisi, simWeight, norms);
           }
         }
 
@@ -575,18 +580,21 @@ private static class SynonymScorer extends Scorer {
     private final DocIdSetIterator iterator;
     private final MaxScoreCache maxScoreCache;
     private final ImpactsDISI impactsDisi;
-    private final LeafSimScorer simScorer;
+    private final SimScorer scorer;
+    private final NumericDocValues norms;
 
     SynonymScorer(
         DisiPriorityQueue queue,
         DocIdSetIterator iterator,
         ImpactsDISI impactsDisi,
-        LeafSimScorer simScorer) {
+        SimScorer scorer,
+        NumericDocValues norms) {
       this.queue = queue;
       this.iterator = iterator;
       this.maxScoreCache = impactsDisi.getMaxScoreCache();
       this.impactsDisi = impactsDisi;
-      this.simScorer = simScorer;
+      this.scorer = scorer;
+      this.norms = norms;
     }
 
     @Override
@@ -605,7 +613,11 @@ float freq() throws IOException {
 
     @Override
     public float score() throws IOException {
-      return simScorer.score(iterator.docID(), freq());
+      long norm = 1L;
+      if (norms != null && norms.advanceExact(iterator.docID())) {
+        norm = norms.longValue();
+      }
+      return scorer.score(freq(), norm);
     }
 
     @Override
@@ -647,17 +659,20 @@ float freq() throws IOException {
   private static class FreqBoostTermScorer extends FilterScorer {
     final float boost;
     final TermScorer in;
-    final LeafSimScorer docScorer;
+    final SimScorer scorer;
+    final NumericDocValues norms;
 
-    public FreqBoostTermScorer(float boost, TermScorer in, LeafSimScorer docScorer) {
+    public FreqBoostTermScorer(
+        float boost, TermScorer in, SimScorer scorer, NumericDocValues norms) {
       super(in);
       if (Float.isNaN(boost) || Float.compare(boost, 0f) < 0 || Float.compare(boost, 1f) > 0) {
         throw new IllegalArgumentException(
             "boost must be a positive float between 0 (exclusive) and 1 (inclusive)");
       }
       this.boost = boost;
       this.in = in;
-      this.docScorer = docScorer;
+      this.scorer = scorer;
+      this.norms = norms;
     }
 
     float freq() throws IOException {
@@ -666,8 +681,11 @@ float freq() throws IOException {
 
     @Override
     public float score() throws IOException {
-      assert docID() != DocIdSetIterator.NO_MORE_DOCS;
-      return docScorer.score(in.docID(), freq());
+      long norm = 1L;
+      if (norms != null && norms.advanceExact(in.docID())) {
+        norm = norms.longValue();
+      }
+      return scorer.score(freq(), norm);
     }
 
     @Override