From 36de1278689c9ea26f93d3a283224c946e1e624d Mon Sep 17 00:00:00 2001
From: Luca Cavanna <javanna@users.noreply.github.com>
Date: Thu, 14 Mar 2019 13:04:06 +0100
Subject: [PATCH] CCS: Disable minimizing round-trips when dfs is requested

When using DFS_QUERY_THEN_FETCH search type, the dfs phase is run and
its results are used in the query phase to make scoring accurate.
When using CCS, depending on whether the DFS phase runs in the CCS
coordinating node (like if all shards were local) or in each remote
cluster (when minimizing round-trips), scoring will differ.

This commit disables minimizing round-trips whenever DFS is requested,
as it is not currently  possible to ensure that scoring is accurate in
that case.

Relates to #32125
---
 .../elasticsearch/action/search/TransportSearchAction.java   | 4 ++++
 .../action/search/TransportSearchActionTests.java            | 5 +++++
 2 files changed, 9 insertions(+)

diff --git a/server/src/main/java/org/elasticsearch/action/search/TransportSearchAction.java b/server/src/main/java/org/elasticsearch/action/search/TransportSearchAction.java
index f0626cff5368c..b1aeb945f5887 100644
--- a/server/src/main/java/org/elasticsearch/action/search/TransportSearchAction.java
+++ b/server/src/main/java/org/elasticsearch/action/search/TransportSearchAction.java
@@ -80,6 +80,7 @@
 import java.util.function.Function;
 import java.util.function.LongSupplier;
 
+import static org.elasticsearch.action.search.SearchType.DFS_QUERY_THEN_FETCH;
 import static org.elasticsearch.action.search.SearchType.QUERY_THEN_FETCH;
 
 public class TransportSearchAction extends HandledTransportAction<SearchRequest, SearchResponse> {
@@ -248,6 +249,9 @@ static boolean shouldMinimizeRoundtrips(SearchRequest searchRequest) {
         if (searchRequest.scroll() != null) {
             return false;
         }
+        if (searchRequest.searchType() == DFS_QUERY_THEN_FETCH) {
+            return false;
+        }
         SearchSourceBuilder source = searchRequest.source();
         return source == null || source.collapse() == null || source.collapse().getInnerHits() == null ||
             source.collapse().getInnerHits().isEmpty();
diff --git a/server/src/test/java/org/elasticsearch/action/search/TransportSearchActionTests.java b/server/src/test/java/org/elasticsearch/action/search/TransportSearchActionTests.java
index 9fb3358b29f13..912ebd108ce7b 100644
--- a/server/src/test/java/org/elasticsearch/action/search/TransportSearchActionTests.java
+++ b/server/src/test/java/org/elasticsearch/action/search/TransportSearchActionTests.java
@@ -812,6 +812,11 @@ public void testShouldMinimizeRoundtrips() throws Exception {
             collapseBuilder.setInnerHits(new InnerHitBuilder("inner"));
             assertFalse(TransportSearchAction.shouldMinimizeRoundtrips(searchRequest));
         }
+        {
+            SearchRequest searchRequest = new SearchRequest();
+            searchRequest.searchType(SearchType.DFS_QUERY_THEN_FETCH);
+            assertFalse(TransportSearchAction.shouldMinimizeRoundtrips(searchRequest));
+        }
         {
             SearchRequestTests searchRequestTests = new SearchRequestTests();
             searchRequestTests.setUp();