Revert "Only consider clauses whose cost is less than the lead cost to compute block boundaries in WANDScorer. (#14000)"

This reverts commit 5807ff1620.

lucene/CHANGES.txt

@@ -70,9 +70,6 @@ Optimizations
 * GITHUB#13994: Speed up top-k retrieval of filtered conjunctions.
   (Adrien Grand)
 
-* GITHUB#13996, GITHUB#14000: Speed up top-k retrieval of filtered disjunctions.
-  (Adrien Grand)
-
 Bug Fixes
 ---------------------
 * GITHUB#13832: Fixed an issue where the DefaultPassageFormatter.format method did not format passages as intended

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

@@ -478,7 +478,7 @@ final class BooleanScorerSupplier extends ScorerSupplier {
       // However, as WANDScorer uses more complex algorithm and data structure, we would like to
       // still use DisjunctionSumScorer to handle exhaustive pure disjunctions, which may be faster
       if ((scoreMode == ScoreMode.TOP_SCORES && topLevelScoringClause) || minShouldMatch > 1) {
-        return new WANDScorer(optionalScorers, minShouldMatch, scoreMode, leadCost);
+        return new WANDScorer(optionalScorers, minShouldMatch, scoreMode);
       } else {
         return new DisjunctionSumScorer(optionalScorers, scoreMode);
       }

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

@@ -149,9 +149,8 @@ final class WANDScorer extends Scorer {
   int freq;
 
   final ScoreMode scoreMode;
-  final long leadCost;
 
-  WANDScorer(Collection<Scorer> scorers, int minShouldMatch, ScoreMode scoreMode, long leadCost)
+  WANDScorer(Collection<Scorer> scorers, int minShouldMatch, ScoreMode scoreMode)
       throws IOException {
 
     if (minShouldMatch >= scorers.size()) {
@@ -203,7 +202,6 @@ final class WANDScorer extends Scorer {
             scorers.stream().map(Scorer::iterator).mapToLong(DocIdSetIterator::cost),
             scorers.size(),
             minShouldMatch);
-    this.leadCost = leadCost;
   }
 
   // returns a boolean so that it can be called from assert
@@ -397,32 +395,26 @@ final class WANDScorer extends Scorer {
   }
 
   private void updateMaxScores(int target) throws IOException {
-    int newUpTo = DocIdSetIterator.NO_MORE_DOCS;
-    // If we have entries in 'head', we treat them all as leads and take the minimum of their next
-    // block boundaries as a next boundary.
-    // We don't take entries in 'tail' into account on purpose: 'tail' is supposed to contain the
-    // least score contributors, and taking them into account might not move the boundary fast
-    // enough, so we'll waste CPU re-computing the next boundary all the time.
-    // Likewise, we ignore clauses whose cost is greater than the lead cost to avoid recomputing
-    // per-window max scores over and over again. In the event when this makes us compute upTo as
-    // NO_MORE_DOCS, this scorer will effectively implement WAND rather than block-max WAND.
-    for (DisiWrapper w : head) {
-      if (w.doc <= newUpTo && w.cost <= leadCost) {
-        newUpTo = Math.min(w.scorer.advanceShallow(w.doc), newUpTo);
-        w.scaledMaxScore = scaleMaxScore(w.scorer.getMaxScore(newUpTo), scalingFactor);
+    if (head.size() == 0) {
+      // If the head is empty we use the greatest score contributor as a lead
+      // like for conjunctions.
+      upTo = tail[0].scorer.advanceShallow(target);
+    } else {
+      // If we still have entries in 'head', we treat them all as leads and
+      // take the minimum of their next block boundaries as a next boundary.
+      // We don't take entries in 'tail' into account on purpose: 'tail' is
+      // supposed to contain the least score contributors, and taking them
+      // into account might not move the boundary fast enough, so we'll waste
+      // CPU re-computing the next boundary all the time.
+      int newUpTo = DocIdSetIterator.NO_MORE_DOCS;
+      for (DisiWrapper w : head) {
+        if (w.doc <= newUpTo) {
+          newUpTo = Math.min(w.scorer.advanceShallow(w.doc), newUpTo);
+          w.scaledMaxScore = scaleMaxScore(w.scorer.getMaxScore(newUpTo), scalingFactor);
+        }
       }
+      upTo = newUpTo;
     }
-    // Only look at the tail if none of the `head` clauses had a block we could reuse and if its
-    // cost is less than or equal to the lead cost.
-    if (newUpTo == DocIdSetIterator.NO_MORE_DOCS && tailSize > 0 && tail[0].cost <= leadCost) {
-      newUpTo = tail[0].scorer.advanceShallow(target);
-      // upTo must be on or after the least `head` doc
-      DisiWrapper headTop = head.top();
-      if (headTop != null) {
-        newUpTo = Math.max(newUpTo, headTop.doc);
-      }
-    }
-    upTo = newUpTo;
 
     tailMaxScore = 0;
     for (int i = 0; i < tailSize; ++i) {
@@ -468,7 +460,8 @@ final class WANDScorer extends Scorer {
       }
     }
 
-    assert head.size() == 0 || head.top().doc <= upTo;
+    assert (head.size() == 0 && upTo == DocIdSetIterator.NO_MORE_DOCS)
+        || (head.size() > 0 && head.top().doc <= upTo);
     assert upTo >= target;
   }
 

lucene/core/src/test/org/apache/lucene/search/TestWANDScorer.java

@@ -1024,11 +1024,7 @@ public class TestWANDScorer extends LuceneTestCase {
           final Scorer scorer;
           if (optionalScorers.size() > 0) {
             scorer =
-                new WANDScorer(
-                    optionalScorers,
-                    query.getMinimumNumberShouldMatch(),
-                    scoreMode,
-                    Long.MAX_VALUE);
+                new WANDScorer(optionalScorers, query.getMinimumNumberShouldMatch(), scoreMode);
           } else {
             scorer = weight.scorer(context);
             if (scorer == null) return null;