Fix ES|QL search context creation to use correct results type (#137994)

The ES|QL search context was being created with an incorrect results type, which unintentionally disabled the inner executor in the Lucene index searcher. This hadn’t caused issues previously because parallelisation happens outside the index searcher for most queries, but KNN queries rely on the internal executor for proper parallel rewrite execution.

This change ensures that the correct results type is used so KNN queries executed via ES|QL can leverage the inner executor and parallelise their rewrite phase correctly.

Author: jimczi

server/src/main/java/org/elasticsearch/search/SearchService.java

@@ -1451,7 +1451,8 @@ public SearchContext createSearchContext(ShardSearchRequest request, TimeValue t
         final Engine.SearcherSupplier reader = indexShard.acquireSearcherSupplier();
         final ShardSearchContextId id = new ShardSearchContextId(sessionId, idGenerator.incrementAndGet(), reader.getSearcherId());
         try (ReaderContext readerContext = new ReaderContext(id, indexService, indexShard, reader, -1L, true)) {
-            DefaultSearchContext searchContext = createSearchContext(readerContext, request, timeout, ResultsType.NONE);
+            // Use ResultsType.QUERY so that the created search context can execute queries correctly.
+            DefaultSearchContext searchContext = createSearchContext(readerContext, request, timeout, ResultsType.QUERY);
             searchContext.addReleasable(readerContext.markAsUsed(0L));
             return searchContext;
         }

server/src/test/java/org/elasticsearch/search/SearchServiceSingleNodeTests.java

@@ -2001,6 +2001,7 @@ public void testCreateSearchContext() throws IOException {
             clusterAlias
         );
         try (SearchContext searchContext = service.createSearchContext(request, new TimeValue(System.currentTimeMillis()))) {
+            assertTrue(searchContext.searcher().hasExecutor());
             SearchShardTarget searchShardTarget = searchContext.shardTarget();
             SearchExecutionContext searchExecutionContext = searchContext.getSearchExecutionContext();
             String expectedIndexName = clusterAlias == null ? index : clusterAlias + ":" + index;