Ensure top docs optimization is fully disabled for queries with unbou…

…nded max scores. (elastic#46105)

When a query contains a mandatory clause that doesn't track the max score per
block, we disable the max score optimization. Previously, we were doing this by
wrapping the collector with a FilterCollector that always returned
ScoreMode.COMPLETE.

However we weren't adjusting totalHitsThreshold, so the collector could still
call Scorer#setMinCompetitiveScore. It is against the method contract to call
setMinCompetitiveScore when the score mode is COMPLETE, and some scorers like
ReqOptSumScorer throw an error in this case.

This commit tries to disable the optimization by always setting
totalHitsThreshold to max int, as opposed to wrapping the collector.

server/src/main/java/org/elasticsearch/search/query/TopDocsCollectorContext.java

@@ -33,13 +33,11 @@
 import org.apache.lucene.search.ConstantScoreQuery;
 import org.apache.lucene.search.DocValuesFieldExistsQuery;
 import org.apache.lucene.search.FieldDoc;
-import org.apache.lucene.search.FilterCollector;
 import org.apache.lucene.search.MatchAllDocsQuery;
 import org.apache.lucene.search.MultiCollector;
 import org.apache.lucene.search.Query;
 import org.apache.lucene.search.QueryVisitor;
 import org.apache.lucene.search.ScoreDoc;
-import org.apache.lucene.search.ScoreMode;
 import org.apache.lucene.search.Sort;
 import org.apache.lucene.search.SortField;
 import org.apache.lucene.search.TermQuery;
@@ -238,7 +236,15 @@ private SimpleTopDocsCollectorContext(IndexReader reader,
             this.sortAndFormats = sortAndFormats;
 
             final TopDocsCollector<?> topDocsCollector;
-            if (trackTotalHitsUpTo == SearchContext.TRACK_TOTAL_HITS_DISABLED) {
+
+            if ((sortAndFormats == null || SortField.FIELD_SCORE.equals(sortAndFormats.sort.getSort()[0]))
+                    && hasInfMaxScore(query)) {
+                // disable max score optimization since we have a mandatory clause
+                // that doesn't track the maximum score
+                topDocsCollector = createCollector(sortAndFormats, numHits, searchAfter, Integer.MAX_VALUE);
+                topDocsSupplier = new CachedSupplier<>(topDocsCollector::topDocs);
+                totalHitsSupplier = () -> topDocsSupplier.get().totalHits;
+            } else if (trackTotalHitsUpTo == SearchContext.TRACK_TOTAL_HITS_DISABLED) {
                 // don't compute hit counts via the collector
                 topDocsCollector = createCollector(sortAndFormats, numHits, searchAfter, 1);
                 topDocsSupplier = new CachedSupplier<>(topDocsCollector::topDocs);
@@ -274,27 +280,7 @@ private SimpleTopDocsCollectorContext(IndexReader reader,
                 maxScoreSupplier = () -> Float.NaN;
             }
 
-            final Collector collector = MultiCollector.wrap(topDocsCollector, maxScoreCollector);
-            if (sortAndFormats == null ||
-                    SortField.FIELD_SCORE.equals(sortAndFormats.sort.getSort()[0])) {
-                if (hasInfMaxScore(query)) {
-                    // disable max score optimization since we have a mandatory clause
-                    // that doesn't track the maximum score
-                    this.collector = new FilterCollector(collector) {
-                        @Override
-                        public ScoreMode scoreMode() {
-                            if (in.scoreMode() == ScoreMode.TOP_SCORES) {
-                                return ScoreMode.COMPLETE;
-                            }
-                            return in.scoreMode();
-                        }
-                    };
-                } else {
-                    this.collector = collector;
-                }
-            } else {
-                this.collector = collector;
-            }
+            this.collector = MultiCollector.wrap(topDocsCollector, maxScoreCollector);
 
         }
 

server/src/test/java/org/elasticsearch/search/query/QueryPhaseTests.java

@@ -606,15 +606,16 @@ public void testDisableTopScoreCollection() throws Exception {
             .build();
 
         context.parsedQuery(new ParsedQuery(q));
-        context.setSize(10);
+        context.setSize(3);
+        context.trackTotalHitsUpTo(3);
+
         TopDocsCollectorContext topDocsContext =
             TopDocsCollectorContext.createTopDocsCollectorContext(context, reader, false);
         assertEquals(topDocsContext.create(null).scoreMode(), org.apache.lucene.search.ScoreMode.COMPLETE);
         QueryPhase.execute(context, contextSearcher, checkCancelled -> {});
         assertEquals(5, context.queryResult().topDocs().topDocs.totalHits.value);
         assertEquals(context.queryResult().topDocs().topDocs.totalHits.relation, TotalHits.Relation.EQUAL_TO);
-        assertThat(context.queryResult().topDocs().topDocs.scoreDocs.length, equalTo(5));
-
+        assertThat(context.queryResult().topDocs().topDocs.scoreDocs.length, equalTo(3));
 
         context.sort(new SortAndFormats(new Sort(new SortField("other", SortField.Type.INT)),
             new DocValueFormat[] { DocValueFormat.RAW }));
@@ -623,7 +624,7 @@ public void testDisableTopScoreCollection() throws Exception {
         assertEquals(topDocsContext.create(null).scoreMode(), org.apache.lucene.search.ScoreMode.COMPLETE_NO_SCORES);
         QueryPhase.execute(context, contextSearcher, checkCancelled -> {});
         assertEquals(5, context.queryResult().topDocs().topDocs.totalHits.value);
-        assertThat(context.queryResult().topDocs().topDocs.scoreDocs.length, equalTo(5));
+        assertThat(context.queryResult().topDocs().topDocs.scoreDocs.length, equalTo(3));
         assertEquals(context.queryResult().topDocs().topDocs.totalHits.relation, TotalHits.Relation.EQUAL_TO);
 
         reader.close();