Indices API: Fix wrong search stats groups

This provides a fix to issue #7644. A new Stats object must be created, and
not a reference to the retrieved stats, before we can add stats to it.
Otherwise, we would keep on adding to the same object on subsequent calls to
IndicesStatsResponse#getPrimaries() or IndicesStatsResponse#getTotal().

Closes #7644 and #8950

src/main/java/org/elasticsearch/index/search/stats/SearchStats.java

@@ -60,6 +60,10 @@ public class SearchStats implements Streamable, ToXContent {
             this.fetchCurrent = fetchCurrent;
         }
 
+        public Stats(Stats stats) {
+            this(stats.queryCount, stats.queryTimeInMillis, stats.queryCurrent, stats.fetchCount, stats.fetchTimeInMillis, stats.fetchCurrent);
+        }
+
         public void add(Stats stats) {
             queryCount += stats.queryCount;
             queryTimeInMillis += stats.queryTimeInMillis;
@@ -178,7 +182,7 @@ public class SearchStats implements Streamable, ToXContent {
             for (Map.Entry<String, Stats> entry : searchStats.groupStats.entrySet()) {
                 Stats stats = groupStats.get(entry.getKey());
                 if (stats == null) {
-                    groupStats.put(entry.getKey(), entry.getValue());
+                    groupStats.put(entry.getKey(), new Stats(entry.getValue()));
                 } else {
                     stats.add(entry.getValue());
                 }

src/test/java/org/elasticsearch/search/stats/SearchStatsUnitTests.java

@@ -0,0 +1,66 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.elasticsearch.search.stats;
+
+import org.elasticsearch.index.search.stats.SearchStats;
+import org.elasticsearch.index.search.stats.SearchStats.Stats;
+import org.elasticsearch.test.ElasticsearchTestCase;
+import org.junit.Test;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class SearchStatsUnitTests extends ElasticsearchTestCase {
+
+    @Test
+    // https://github.com/elasticsearch/elasticsearch/issues/7644
+    public void testShardLevelSearchGroupStats() throws Exception {
+        // let's create two dummy search stats with groups
+        Map<String, Stats> groupStats1 = new HashMap<>();
+        Map<String, Stats> groupStats2 = new HashMap<>();
+        groupStats2.put("group1", new Stats(1, 1, 1, 1, 1, 1));
+        SearchStats searchStats1 = new SearchStats(new Stats(1, 1, 1, 1, 1, 1), 0, groupStats1);
+        SearchStats searchStats2 = new SearchStats(new Stats(1, 1, 1, 1, 1, 1), 0, groupStats2);
+
+        // adding these two search stats and checking group stats are correct
+        searchStats1.add(searchStats2);
+        assertStats(groupStats1.get("group1"), 1);
+
+        // another call, adding again ...
+        searchStats1.add(searchStats2);
+        assertStats(groupStats1.get("group1"), 2);
+
+        // making sure stats2 was not affected (this would previously return 2!)
+        assertStats(groupStats2.get("group1"), 1);
+
+        // adding again would then return wrong search stats (would return 4! instead of 3)
+        searchStats1.add(searchStats2);
+        assertStats(groupStats1.get("group1"), 3);
+    }
+
+    private void assertStats(Stats stats, long equalTo) {
+        assertEquals(equalTo, stats.getQueryCount());
+        assertEquals(equalTo, stats.getQueryTimeInMillis());
+        assertEquals(equalTo, stats.getQueryCurrent());
+        assertEquals(equalTo, stats.getFetchCount());
+        assertEquals(equalTo, stats.getFetchTimeInMillis());
+        assertEquals(equalTo, stats.getFetchCurrent());
+    }
+}