Add finalReduce flag to SearchRequest (6.x) (#38180)

Backport of #38104 to 6.x

This commit adds support for a separate finalReduce flag to
SearchRequest and makes use of it in SearchPhaseController instead of
disabling final reduction whenever a cluster alias is provided.

Relates to #38104

Author: javanna

server/src/main/java/org/elasticsearch/action/search/SearchPhaseController.java

@@ -712,19 +712,19 @@ InitialSearchPhase.ArraySearchPhaseResults<SearchPhaseResult> newSearchPhaseResu
         final boolean hasAggs = source != null && source.aggregations() != null;
         final boolean hasTopDocs = source == null || source.size() != 0;
         final boolean trackTotalHits = source == null || source.trackTotalHits();
-        final boolean finalReduce = request.getLocalClusterAlias() == null;
 
         if (isScrollRequest == false && (hasAggs || hasTopDocs)) {
             // no incremental reduce if scroll is used - we only hit a single shard or sometimes more...
             if (request.getBatchedReduceSize() < numShards) {
                 // only use this if there are aggs and if there are more shards than we should reduce at once
-                return new QueryPhaseResultConsumer(this, numShards, request.getBatchedReduceSize(), hasTopDocs, hasAggs, finalReduce);
+                return new QueryPhaseResultConsumer(this, numShards, request.getBatchedReduceSize(), hasTopDocs, hasAggs,
+                    request.isFinalReduce());
             }
         }
         return new InitialSearchPhase.ArraySearchPhaseResults<SearchPhaseResult>(numShards) {
             @Override
             ReducedQueryPhase reduce() {
-                return reducedQueryPhase(results.asList(), isScrollRequest, trackTotalHits, finalReduce);
+                return reducedQueryPhase(results.asList(), isScrollRequest, trackTotalHits, request.isFinalReduce());
             }
         };
     }

server/src/main/java/org/elasticsearch/action/search/SearchRequest.java

@@ -69,6 +69,7 @@ public final class SearchRequest extends ActionRequest implements IndicesRequest
 
     private String localClusterAlias;
     private long absoluteStartMillis;
+    private boolean finalReduce;
 
     private SearchType searchType = SearchType.DEFAULT;
 
@@ -102,6 +103,7 @@ public final class SearchRequest extends ActionRequest implements IndicesRequest
     public SearchRequest() {
         this.localClusterAlias = null;
         this.absoluteStartMillis = DEFAULT_ABSOLUTE_START_MILLIS;
+        this.finalReduce = true;
     }
 
     /**
@@ -123,6 +125,7 @@ public SearchRequest(SearchRequest searchRequest) {
         this.types = searchRequest.types;
         this.localClusterAlias = searchRequest.localClusterAlias;
         this.absoluteStartMillis = searchRequest.absoluteStartMillis;
+        this.finalReduce = searchRequest.finalReduce;
     }
 
     /**
@@ -147,16 +150,18 @@ public SearchRequest(String[] indices, SearchSourceBuilder source) {
 
     /**
      * Creates a new search request by providing the alias of the cluster where it will be executed, as well as the current time in
-     * milliseconds from the epoch time. Used when a {@link SearchRequest} is created and executed as part of a cross-cluster search
-     * request performing local reduction on each cluster. The coordinating CCS node provides the alias to prefix index names with in
-     * the returned search results, and the current time to be used on the remote clusters to ensure that the same value is used.
+     * milliseconds from the epoch time and whether the reduction should be final or not. Used when a {@link SearchRequest} is created
+     * and executed as part of a cross-cluster search request performing reduction on each remote cluster. The coordinating CCS node
+     * provides the alias to prefix index names with in the returned search results, the current time to be used on the remote clusters
+     * to ensure that the same value is used, and determines whether the reduction phase should be final or not.
      */
-    SearchRequest(String localClusterAlias, long absoluteStartMillis) {
+    SearchRequest(String localClusterAlias, long absoluteStartMillis, boolean finalReduce) {
         this.localClusterAlias = Objects.requireNonNull(localClusterAlias, "cluster alias must not be null");
         if (absoluteStartMillis < 0) {
             throw new IllegalArgumentException("absoluteStartMillis must not be negative but was [" + absoluteStartMillis + "]");
         }
         this.absoluteStartMillis = absoluteStartMillis;
+        this.finalReduce = finalReduce;
     }
 
     @Override
@@ -195,10 +200,17 @@ String getLocalClusterAlias() {
         return localClusterAlias;
     }
 
+    /**
+     * Returns whether the reduction phase that will be performed needs to be final or not.
+     */
+    boolean isFinalReduce() {
+        return finalReduce;
+    }
+
     /**
      * Returns the current time in milliseconds from the time epoch, to be used for the execution of this search request. Used to
      * ensure that the same value, determined by the coordinating node, is used on all nodes involved in the execution of the search
-     * request. When created through {@link #SearchRequest(String, long)}, this method returns the provided current time, otherwise
+     * request. When created through {@link #SearchRequest(String, long, boolean)}, this method returns the provided current time, otherwise
      * it will return {@link System#currentTimeMillis()}.
      *
      */
@@ -518,12 +530,15 @@ public void readFrom(StreamInput in) throws IOException {
             localClusterAlias = in.readOptionalString();
             if (localClusterAlias != null) {
                 absoluteStartMillis = in.readVLong();
+                finalReduce = in.readBoolean();
             } else {
                 absoluteStartMillis = DEFAULT_ABSOLUTE_START_MILLIS;
+                finalReduce = true;
             }
         } else {
             localClusterAlias = null;
             absoluteStartMillis = DEFAULT_ABSOLUTE_START_MILLIS;
+            finalReduce = true;
         }
     }
 
@@ -554,6 +569,7 @@ public void writeTo(StreamOutput out) throws IOException {
             out.writeOptionalString(localClusterAlias);
             if (localClusterAlias != null) {
                 out.writeVLong(absoluteStartMillis);
+                out.writeBoolean(finalReduce);
             }
         }
     }

server/src/test/java/org/elasticsearch/action/search/SearchPhaseControllerTests.java

@@ -306,9 +306,13 @@ private static AtomicArray<SearchPhaseResult> generateFetchResults(int nShards,
         return fetchResults;
     }
 
+    private static SearchRequest randomSearchRequest() {
+        return randomBoolean() ? new SearchRequest() : new SearchRequest("remote", 0, randomBoolean());
+    }
+
     public void testConsumer() {
         int bufferSize = randomIntBetween(2, 3);
-        SearchRequest request = randomBoolean() ? new SearchRequest() : new SearchRequest("remote");
+        SearchRequest request = randomSearchRequest();
         request.source(new SearchSourceBuilder().aggregation(AggregationBuilders.avg("foo")));
         request.setBatchedReduceSize(bufferSize);
         InitialSearchPhase.ArraySearchPhaseResults<SearchPhaseResult> consumer = searchPhaseController.newSearchPhaseResults(request, 3);
@@ -366,7 +370,7 @@ public void testConsumerConcurrently() throws InterruptedException {
         int expectedNumResults = randomIntBetween(1, 100);
         int bufferSize = randomIntBetween(2, 200);
 
-        SearchRequest request = randomBoolean() ? new SearchRequest() : new SearchRequest("remote");
+        SearchRequest request = randomSearchRequest();
         request.source(new SearchSourceBuilder().aggregation(AggregationBuilders.avg("foo")));
         request.setBatchedReduceSize(bufferSize);
         InitialSearchPhase.ArraySearchPhaseResults<SearchPhaseResult> consumer =
@@ -410,7 +414,7 @@ public void testConsumerConcurrently() throws InterruptedException {
     public void testConsumerOnlyAggs() {
         int expectedNumResults = randomIntBetween(1, 100);
         int bufferSize = randomIntBetween(2, 200);
-        SearchRequest request = randomBoolean() ? new SearchRequest() : new SearchRequest("remote");
+        SearchRequest request = randomSearchRequest();
         request.source(new SearchSourceBuilder().aggregation(AggregationBuilders.avg("foo")).size(0));
         request.setBatchedReduceSize(bufferSize);
         InitialSearchPhase.ArraySearchPhaseResults<SearchPhaseResult> consumer =
@@ -444,7 +448,7 @@ public void testConsumerOnlyAggs() {
     public void testConsumerOnlyHits() {
         int expectedNumResults = randomIntBetween(1, 100);
         int bufferSize = randomIntBetween(2, 200);
-        SearchRequest request = randomBoolean() ? new SearchRequest() : new SearchRequest("remote");
+        SearchRequest request = randomSearchRequest();
         if (randomBoolean()) {
             request.source(new SearchSourceBuilder().size(randomIntBetween(1, 10)));
         }
@@ -475,8 +479,7 @@ public void testConsumerOnlyHits() {
 
     private void assertFinalReduction(SearchRequest searchRequest) {
         assertThat(reductions.size(), greaterThanOrEqualTo(1));
-        //the last reduction step was the final one only if no cluster alias was provided with the search request
-        assertEquals(searchRequest.getLocalClusterAlias() == null, reductions.get(reductions.size() - 1));
+        assertEquals(searchRequest.isFinalReduce(), reductions.get(reductions.size() - 1));
     }
 
     public void testNewSearchPhaseResults() {
@@ -548,7 +551,7 @@ public void testReduceTopNWithFromOffset() {
     public void testConsumerSortByField() {
         int expectedNumResults = randomIntBetween(1, 100);
         int bufferSize = randomIntBetween(2, 200);
-        SearchRequest request = randomBoolean() ? new SearchRequest() : new SearchRequest("remote");
+        SearchRequest request = randomSearchRequest();
         int size = randomIntBetween(1, 10);
         request.setBatchedReduceSize(bufferSize);
         InitialSearchPhase.ArraySearchPhaseResults<SearchPhaseResult> consumer =
@@ -583,7 +586,7 @@ public void testConsumerSortByField() {
     public void testConsumerFieldCollapsing() {
         int expectedNumResults = randomIntBetween(30, 100);
         int bufferSize = randomIntBetween(2, 200);
-        SearchRequest request = randomBoolean() ? new SearchRequest() : new SearchRequest("remote");
+        SearchRequest request = randomSearchRequest();
         int size = randomIntBetween(5, 10);
         request.setBatchedReduceSize(bufferSize);
         InitialSearchPhase.ArraySearchPhaseResults<SearchPhaseResult> consumer =

server/src/test/java/org/elasticsearch/action/search/SearchRequestTests.java

@@ -52,15 +52,15 @@ protected SearchRequest createSearchRequest() throws IOException {
             return super.createSearchRequest();
         }
         //clusterAlias and absoluteStartMillis do not have public getters/setters hence we randomize them only in this test specifically.
-        SearchRequest searchRequest = new SearchRequest(randomAlphaOfLengthBetween(5, 10), randomNonNegativeLong());
+        SearchRequest searchRequest = new SearchRequest(randomAlphaOfLengthBetween(5, 10), randomNonNegativeLong(), randomBoolean());
         RandomSearchRequestGenerator.randomSearchRequest(searchRequest, this::createSearchSourceBuilder);
         return searchRequest;
     }
 
     public void testClusterAliasValidation() {
-        expectThrows(NullPointerException.class, () -> new SearchRequest(null, 0));
-        expectThrows(IllegalArgumentException.class, () -> new SearchRequest("", -1));
-        SearchRequest searchRequest = new SearchRequest("", 0);
+        expectThrows(NullPointerException.class, () -> new SearchRequest(null, 0, randomBoolean()));
+        expectThrows(IllegalArgumentException.class, () -> new SearchRequest("", -1, randomBoolean()));
+        SearchRequest searchRequest = new SearchRequest("", 0, randomBoolean());
         assertNull(searchRequest.validate());
     }
 
@@ -79,9 +79,11 @@ public void testClusterAliasSerialization() throws IOException {
         if (version.before(Version.V_6_7_0)) {
             assertNull(deserializedRequest.getLocalClusterAlias());
             assertAbsoluteStartMillisIsCurrentTime(deserializedRequest);
+            assertTrue(deserializedRequest.isFinalReduce());
         } else {
             assertEquals(searchRequest.getLocalClusterAlias(), deserializedRequest.getLocalClusterAlias());
             assertEquals(searchRequest.getOrCreateAbsoluteStartMillis(), deserializedRequest.getOrCreateAbsoluteStartMillis());
+            assertEquals(searchRequest.isFinalReduce(), deserializedRequest.isFinalReduce());
         }
     }
 
@@ -94,6 +96,7 @@ public void testReadFromPre6_7_0() throws IOException {
             assertArrayEquals(new String[]{"index"}, searchRequest.indices());
             assertNull(searchRequest.getLocalClusterAlias());
             assertAbsoluteStartMillisIsCurrentTime(searchRequest);
+            assertTrue(searchRequest.isFinalReduce());
         }
     }
 

server/src/test/java/org/elasticsearch/action/search/TransportSearchActionSingleNodeTests.java

@@ -26,21 +26,25 @@
 import org.elasticsearch.index.query.RangeQueryBuilder;
 import org.elasticsearch.rest.RestStatus;
 import org.elasticsearch.search.SearchHit;
+import org.elasticsearch.search.aggregations.Aggregations;
+import org.elasticsearch.search.aggregations.bucket.terms.LongTerms;
+import org.elasticsearch.search.aggregations.bucket.terms.TermsAggregationBuilder;
+import org.elasticsearch.search.aggregations.support.ValueType;
 import org.elasticsearch.search.builder.SearchSourceBuilder;
 import org.elasticsearch.test.ESSingleNodeTestCase;
 
 public class TransportSearchActionSingleNodeTests extends ESSingleNodeTestCase {
 
     public void testLocalClusterAlias() {
-        long nowInMillis = System.currentTimeMillis();
+        long nowInMillis = randomLongBetween(0, Long.MAX_VALUE);
         IndexRequest indexRequest = new IndexRequest("test", "type", "1");
         indexRequest.source("field", "value");
         indexRequest.setRefreshPolicy(WriteRequest.RefreshPolicy.WAIT_UNTIL);
         IndexResponse indexResponse = client().index(indexRequest).actionGet();
         assertEquals(RestStatus.CREATED, indexResponse.status());
 
         {
-            SearchRequest searchRequest = new SearchRequest("local", nowInMillis);
+            SearchRequest searchRequest = new SearchRequest("local", nowInMillis, randomBoolean());
             SearchResponse searchResponse = client().search(searchRequest).actionGet();
             assertEquals(1, searchResponse.getHits().getTotalHits());
             SearchHit[] hits = searchResponse.getHits().getHits();
@@ -51,7 +55,7 @@ public void testLocalClusterAlias() {
             assertEquals("1", hit.getId());
         }
         {
-            SearchRequest searchRequest = new SearchRequest("", nowInMillis);
+            SearchRequest searchRequest = new SearchRequest("", nowInMillis, randomBoolean());
             SearchResponse searchResponse = client().search(searchRequest).actionGet();
             assertEquals(1, searchResponse.getHits().getTotalHits());
             SearchHit[] hits = searchResponse.getHits().getHits();
@@ -90,19 +94,19 @@ public void testAbsoluteStartMillis() {
             assertEquals(0, searchResponse.getTotalShards());
         }
         {
-            SearchRequest searchRequest = new SearchRequest("", 0);
+            SearchRequest searchRequest = new SearchRequest("", 0, randomBoolean());
             SearchResponse searchResponse = client().search(searchRequest).actionGet();
             assertEquals(2, searchResponse.getHits().getTotalHits());
         }
         {
-            SearchRequest searchRequest = new SearchRequest("", 0);
+            SearchRequest searchRequest = new SearchRequest("", 0, randomBoolean());
             searchRequest.indices("<test-{now/d}>");
             SearchResponse searchResponse = client().search(searchRequest).actionGet();
             assertEquals(1, searchResponse.getHits().getTotalHits());
             assertEquals("test-1970.01.01", searchResponse.getHits().getHits()[0].getIndex());
         }
         {
-            SearchRequest searchRequest = new SearchRequest("", 0);
+            SearchRequest searchRequest = new SearchRequest("", 0, randomBoolean());
             SearchSourceBuilder sourceBuilder = new SearchSourceBuilder();
             RangeQueryBuilder rangeQuery = new RangeQueryBuilder("date");
             rangeQuery.gte("1970-01-01");
@@ -114,4 +118,46 @@ public void testAbsoluteStartMillis() {
             assertEquals("test-1970.01.01", searchResponse.getHits().getHits()[0].getIndex());
         }
     }
+
+    public void testFinalReduce()  {
+        long nowInMillis = randomLongBetween(0, Long.MAX_VALUE);
+        {
+            IndexRequest indexRequest = new IndexRequest("test", "type", "1");
+            indexRequest.source("price", 10);
+            IndexResponse indexResponse = client().index(indexRequest).actionGet();
+            assertEquals(RestStatus.CREATED, indexResponse.status());
+        }
+        {
+            IndexRequest indexRequest = new IndexRequest("test", "type", "2");
+            indexRequest.source("price", 100);
+            IndexResponse indexResponse = client().index(indexRequest).actionGet();
+            assertEquals(RestStatus.CREATED, indexResponse.status());
+        }
+        client().admin().indices().prepareRefresh("test").get();
+
+        SearchSourceBuilder source = new SearchSourceBuilder();
+        source.size(0);
+        TermsAggregationBuilder terms = new TermsAggregationBuilder("terms", ValueType.NUMERIC);
+        terms.field("price");
+        terms.size(1);
+        source.aggregation(terms);
+
+        {
+            SearchRequest searchRequest = randomBoolean() ? new SearchRequest().source(source)
+                : new SearchRequest("remote", nowInMillis, true).source(source);
+            SearchResponse searchResponse = client().search(searchRequest).actionGet();
+            assertEquals(2, searchResponse.getHits().getTotalHits());
+            Aggregations aggregations = searchResponse.getAggregations();
+            LongTerms longTerms = aggregations.get("terms");
+            assertEquals(1, longTerms.getBuckets().size());
+        }
+        {
+            SearchRequest searchRequest = new SearchRequest("remote", nowInMillis, false).source(source);
+            SearchResponse searchResponse = client().search(searchRequest).actionGet();
+            assertEquals(2, searchResponse.getHits().getTotalHits());
+            Aggregations aggregations = searchResponse.getAggregations();
+            LongTerms longTerms = aggregations.get("terms");
+            assertEquals(2, longTerms.getBuckets().size());
+        }
+    }
 }