Re-enable parallel collection for field sorted top hits

docs/changelog/125916.yaml

@@ -0,0 +1,5 @@
+pr: 125916
+summary: Re-enable parallel collection for field sorted top hits
+area: Search
+type: bug
+issues: []

server/src/main/java/org/elasticsearch/search/aggregations/metrics/TopHitsAggregationBuilder.java

@@ -49,7 +49,6 @@
 import java.util.Objects;
 import java.util.Optional;
 import java.util.Set;
-import java.util.function.ToLongFunction;
 
 public class TopHitsAggregationBuilder extends AbstractAggregationBuilder<TopHitsAggregationBuilder> {
     public static final String NAME = "top_hits";
@@ -823,18 +822,4 @@ public String getType() {
     public TransportVersion getMinimalSupportedVersion() {
         return TransportVersions.ZERO;
     }
-
-    @Override
-    public boolean supportsParallelCollection(ToLongFunction<String> fieldCardinalityResolver) {
-        if (sorts != null) {
-            // the implicit sorting is by _score, which supports parallel collection
-            for (SortBuilder<?> sortBuilder : sorts) {
-                if (sortBuilder.supportsParallelCollection() == false) {
-                    return false;
-                }
-            }
-        }
-
-        return super.supportsParallelCollection(fieldCardinalityResolver);
-    }
 }

server/src/main/java/org/elasticsearch/search/sort/FieldSortBuilder.java

@@ -741,4 +741,11 @@ public FieldSortBuilder rewrite(QueryRewriteContext ctx) throws IOException {
         }
         return new FieldSortBuilder(this).setNestedSort(rewrite);
     }
+
+    @Override
+    public boolean supportsParallelCollection() {
+        // Disable parallel collection for sort by field.
+        // It is supported but not optimized on the Lucene side to share info across collectors, and can cause regressions.
+        return false;
+    }
 }

server/src/main/java/org/elasticsearch/search/sort/GeoDistanceSortBuilder.java

@@ -721,4 +721,11 @@ public GeoDistanceSortBuilder rewrite(QueryRewriteContext ctx) throws IOExceptio
         }
         return new GeoDistanceSortBuilder(this).setNestedSort(rewrite);
     }
+
+    @Override
+    public boolean supportsParallelCollection() {
+        // Disable parallel collection for sort by field.
+        // It is supported but not optimized on the Lucene side to share info across collectors, and can cause regressions.
+        return false;
+    }
 }

server/src/main/java/org/elasticsearch/search/sort/ScoreSortBuilder.java

@@ -172,9 +172,4 @@ public TransportVersion getMinimalSupportedVersion() {
     public ScoreSortBuilder rewrite(QueryRewriteContext ctx) {
         return this;
     }
-
-    @Override
-    public boolean supportsParallelCollection() {
-        return true;
-    }
 }

server/src/main/java/org/elasticsearch/search/sort/ScriptSortBuilder.java

@@ -502,9 +502,4 @@ public ScriptSortBuilder rewrite(QueryRewriteContext ctx) throws IOException {
         }
         return new ScriptSortBuilder(this).setNestedSort(rewrite);
     }
-
-    @Override
-    public boolean supportsParallelCollection() {
-        return true;
-    }
 }

server/src/main/java/org/elasticsearch/search/sort/SortBuilder.java

@@ -285,6 +285,6 @@ public String toString() {
     }
 
     public boolean supportsParallelCollection() {
-        return false;
+        return true;
     }
 }

server/src/test/java/org/elasticsearch/search/builder/SearchSourceBuilderTests.java

@@ -1007,7 +1007,7 @@ public void testSupportsParallelCollection() {
         {
             SearchSourceBuilder searchSourceBuilder = newSearchSourceBuilder.get();
             searchSourceBuilder.aggregation(new TopHitsAggregationBuilder("tophits").sort(SortBuilders.fieldSort("field")));
-            assertFalse(searchSourceBuilder.supportsParallelCollection(fieldCardinality));
+            assertTrue(searchSourceBuilder.supportsParallelCollection(fieldCardinality));
         }
         {
             SearchSourceBuilder searchSourceBuilder = newSearchSourceBuilder.get();