Avoid making further transport calls if paginationStrategy outputs empty entities (#16444)

Signed-off-by: Harsh Garg <[email protected]>
(cherry picked from commit 9a476b6)
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]

server/src/main/java/org/opensearch/action/admin/cluster/shards/TransportCatShardsAction.java

@@ -108,6 +108,12 @@ public void onResponse(ClusterStateResponse clusterStateResponse) {
                                 : paginationStrategy.getRequestedEntities()
                         );
                         catShardsResponse.setPageToken(Objects.isNull(paginationStrategy) ? null : paginationStrategy.getResponseToken());
+                        // For paginated queries, if strategy outputs no shards to be returned, avoid fetching IndicesStats.
+                        if (shouldSkipIndicesStatsRequest(paginationStrategy)) {
+                            catShardsResponse.setIndicesStatsResponse(IndicesStatsResponse.getEmptyResponse());
+                            cancellableListener.onResponse(catShardsResponse);
+                            return;
+                        }
                         IndicesStatsRequest indicesStatsRequest = new IndicesStatsRequest();
                         indicesStatsRequest.setShouldCancelOnTimeout(true);
                         indicesStatsRequest.all();
@@ -159,4 +165,8 @@ private void validateRequestLimit(
             }
         }
     }
+
+    private boolean shouldSkipIndicesStatsRequest(ShardPaginationStrategy paginationStrategy) {
+        return Objects.nonNull(paginationStrategy) && paginationStrategy.getRequestedEntities().isEmpty();
+    }
 }

server/src/main/java/org/opensearch/action/admin/indices/stats/IndicesStatsResponse.java

@@ -45,6 +45,7 @@
 import org.opensearch.core.xcontent.XContentBuilder;
 
 import java.io.IOException;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -230,4 +231,8 @@ static final class Fields {
     public String toString() {
         return Strings.toString(MediaTypeRegistry.JSON, this, true, false);
     }
+
+    public static IndicesStatsResponse getEmptyResponse() {
+        return new IndicesStatsResponse(new ShardStats[0], 0, 0, 0, Collections.emptyList());
+    }
 }

server/src/main/java/org/opensearch/rest/action/cat/RestIndicesAction.java

@@ -205,13 +205,19 @@ public void onResponse(ClusterStateResponse clusterStateResponse) {
                                     groupedListener.onResponse(getSettingsResponse);
                                     groupedListener.onResponse(clusterStateResponse);
 
-                                    sendIndicesStatsRequest(
-                                        indicesToBeQueried,
-                                        subRequestIndicesOptions,
-                                        includeUnloadedSegments,
-                                        client,
-                                        ActionListener.wrap(groupedListener::onResponse, groupedListener::onFailure)
-                                    );
+                                    // For paginated queries, if strategy outputs no indices to be returned,
+                                    // avoid fetching indices stats.
+                                    if (shouldSkipIndicesStatsRequest(paginationStrategy)) {
+                                        groupedListener.onResponse(IndicesStatsResponse.getEmptyResponse());
+                                    } else {
+                                        sendIndicesStatsRequest(
+                                            indicesToBeQueried,
+                                            subRequestIndicesOptions,
+                                            includeUnloadedSegments,
+                                            client,
+                                            ActionListener.wrap(groupedListener::onResponse, groupedListener::onFailure)
+                                        );
+                                    }
 
                                     sendClusterHealthRequest(
                                         indicesToBeQueried,
@@ -1086,4 +1092,8 @@ public Tuple<String, Settings> next() {
         };
     }
 
+    private boolean shouldSkipIndicesStatsRequest(IndexPaginationStrategy paginationStrategy) {
+        return Objects.nonNull(paginationStrategy) && paginationStrategy.getRequestedEntities().isEmpty();
+    }
+
 }