Fix scroll query with a sort that is a prefix of the index sort (#27498)

During a scroll, if the search sort matches the index sort we use the sort values of the last doc returned by
the previous scroll to optimize the main query with a `SearchAfterSortedDocQuery`.
This query can "jump" directly to the first document that sorts after the provided sort values.
This optim is also applied if the search sort is a prefix of the index sort but this case throws an exception
because we use the index sort (instead of the search sort) to validate the sort values of the last document.
This change fixes this bug and adds a test for it.

core/src/main/java/org/elasticsearch/search/query/QueryPhase.java

@@ -162,12 +162,12 @@ static boolean execute(SearchContext searchContext, final IndexSearcher searcher
                         searchContext.terminateAfter(searchContext.size());
                         searchContext.trackTotalHits(false);
                     } else if (canEarlyTerminate(indexSort, searchContext)) {
-                        // now this gets interesting: since the index sort matches the search sort, we can directly
+                        // now this gets interesting: since the search sort is a prefix of the index sort, we can directly
                         // skip to the desired doc
                         if (after != null) {
                             BooleanQuery bq = new BooleanQuery.Builder()
                                 .add(query, BooleanClause.Occur.MUST)
-                                .add(new SearchAfterSortedDocQuery(indexSort, (FieldDoc) after), BooleanClause.Occur.FILTER)
+                                .add(new SearchAfterSortedDocQuery(searchContext.sort().sort, (FieldDoc) after), BooleanClause.Occur.FILTER)
                                 .build();
                             query = bq;
                         }

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

@@ -62,6 +62,7 @@
 import org.elasticsearch.test.TestSearchContext;
 
 import java.io.IOException;
+import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.atomic.AtomicBoolean;
 
@@ -465,11 +466,11 @@ public void testIndexSortingEarlyTermination() throws Exception {
 
     public void testIndexSortScrollOptimization() throws Exception {
         Directory dir = newDirectory();
-        final Sort sort = new Sort(
+        final Sort indexSort = new Sort(
             new SortField("rank", SortField.Type.INT),
             new SortField("tiebreaker", SortField.Type.INT)
         );
-        IndexWriterConfig iwc = newIndexWriterConfig().setIndexSort(sort);
+        IndexWriterConfig iwc = newIndexWriterConfig().setIndexSort(indexSort);
         RandomIndexWriter w = new RandomIndexWriter(random(), dir, iwc);
         final int numDocs = scaledRandomIntBetween(100, 200);
         for (int i = 0; i < numDocs; ++i) {
@@ -483,44 +484,49 @@ public void testIndexSortScrollOptimization() throws Exception {
         }
         w.close();
 
-        TestSearchContext context = new TestSearchContext(null, indexShard);
-        context.parsedQuery(new ParsedQuery(new MatchAllDocsQuery()));
-        ScrollContext scrollContext = new ScrollContext();
-        scrollContext.lastEmittedDoc = null;
-        scrollContext.maxScore = Float.NaN;
-        scrollContext.totalHits = -1;
-        context.scrollContext(scrollContext);
-        context.setTask(new SearchTask(123L, "", "", "", null));
-        context.setSize(10);
-        context.sort(new SortAndFormats(sort, new DocValueFormat[] {DocValueFormat.RAW, DocValueFormat.RAW}));
-
         final IndexReader reader = DirectoryReader.open(dir);
-        IndexSearcher contextSearcher = new IndexSearcher(reader);
-
-        QueryPhase.execute(context, contextSearcher, checkCancelled -> {}, sort);
-        assertThat(context.queryResult().topDocs().totalHits, equalTo((long) numDocs));
-        assertNull(context.queryResult().terminatedEarly());
-        assertThat(context.terminateAfter(), equalTo(0));
-        assertThat(context.queryResult().getTotalHits(), equalTo((long) numDocs));
-        int sizeMinus1 = context.queryResult().topDocs().scoreDocs.length - 1;
-        FieldDoc lastDoc = (FieldDoc) context.queryResult().topDocs().scoreDocs[sizeMinus1];
+        List<SortAndFormats> searchSortAndFormats = new ArrayList<>();
+        searchSortAndFormats.add(new SortAndFormats(indexSort, new DocValueFormat[]{DocValueFormat.RAW, DocValueFormat.RAW}));
+        // search sort is a prefix of the index sort
+        searchSortAndFormats.add(new SortAndFormats(new Sort(indexSort.getSort()[0]), new DocValueFormat[]{DocValueFormat.RAW}));
+        for (SortAndFormats searchSortAndFormat : searchSortAndFormats) {
+            IndexSearcher contextSearcher = new IndexSearcher(reader);
+            TestSearchContext context = new TestSearchContext(null, indexShard);
+            context.parsedQuery(new ParsedQuery(new MatchAllDocsQuery()));
+            ScrollContext scrollContext = new ScrollContext();
+            scrollContext.lastEmittedDoc = null;
+            scrollContext.maxScore = Float.NaN;
+            scrollContext.totalHits = -1;
+            context.scrollContext(scrollContext);
+            context.setTask(new SearchTask(123L, "", "", "", null));
+            context.setSize(10);
+            context.sort(searchSortAndFormat);
+
+            QueryPhase.execute(context, contextSearcher, checkCancelled -> {}, searchSortAndFormat.sort);
+            assertThat(context.queryResult().topDocs().totalHits, equalTo((long) numDocs));
+            assertNull(context.queryResult().terminatedEarly());
+            assertThat(context.terminateAfter(), equalTo(0));
+            assertThat(context.queryResult().getTotalHits(), equalTo((long) numDocs));
+            int sizeMinus1 = context.queryResult().topDocs().scoreDocs.length - 1;
+            FieldDoc lastDoc = (FieldDoc) context.queryResult().topDocs().scoreDocs[sizeMinus1];
 
-        contextSearcher = getAssertingEarlyTerminationSearcher(reader, 10);
-        QueryPhase.execute(context, contextSearcher, checkCancelled -> {}, sort);
-        assertNull(context.queryResult().terminatedEarly());
-        assertThat(context.queryResult().topDocs().totalHits, equalTo((long) numDocs));
-        assertThat(context.terminateAfter(), equalTo(0));
-        assertThat(context.queryResult().getTotalHits(), equalTo((long) numDocs));
-        FieldDoc firstDoc = (FieldDoc) context.queryResult().topDocs().scoreDocs[0];
-        for (int i = 0; i < sort.getSort().length; i++) {
-            @SuppressWarnings("unchecked")
-            FieldComparator<Object> comparator = (FieldComparator<Object>) sort.getSort()[i].getComparator(1, i);
-            int cmp = comparator.compareValues(firstDoc.fields[i], lastDoc.fields[i]);
-            if (cmp == 0) {
-                continue;
+            contextSearcher = getAssertingEarlyTerminationSearcher(reader, 10);
+            QueryPhase.execute(context, contextSearcher, checkCancelled -> {}, searchSortAndFormat.sort);
+            assertNull(context.queryResult().terminatedEarly());
+            assertThat(context.queryResult().topDocs().totalHits, equalTo((long) numDocs));
+            assertThat(context.terminateAfter(), equalTo(0));
+            assertThat(context.queryResult().getTotalHits(), equalTo((long) numDocs));
+            FieldDoc firstDoc = (FieldDoc) context.queryResult().topDocs().scoreDocs[0];
+            for (int i = 0; i < searchSortAndFormat.sort.getSort().length; i++) {
+                @SuppressWarnings("unchecked")
+                FieldComparator<Object> comparator = (FieldComparator<Object>) searchSortAndFormat.sort.getSort()[i].getComparator(1, i);
+                int cmp = comparator.compareValues(firstDoc.fields[i], lastDoc.fields[i]);
+                if (cmp == 0) {
+                    continue;
+                }
+                assertThat(cmp, equalTo(1));
+                break;
             }
-            assertThat(cmp, equalTo(1));
-            break;
         }
         reader.close();
         dir.close();