Avoid making further transport calls if paginationStrategy outputs empty entities

Signed-off-by: Harsh Garg <[email protected]>

Author: Harsh Garg

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

@@ -12,6 +12,7 @@
 import org.opensearch.action.admin.cluster.state.ClusterStateResponse;
 import org.opensearch.action.admin.indices.stats.IndicesStatsRequest;
 import org.opensearch.action.admin.indices.stats.IndicesStatsResponse;
+import org.opensearch.action.admin.indices.stats.ShardStats;
 import org.opensearch.action.pagination.PageParams;
 import org.opensearch.action.pagination.ShardPaginationStrategy;
 import org.opensearch.action.support.ActionFilters;
@@ -27,6 +28,7 @@
 import org.opensearch.tasks.Task;
 import org.opensearch.transport.TransportService;
 
+import java.util.Collections;
 import java.util.Objects;
 
 import static org.opensearch.common.breaker.ResponseLimitSettings.LimitEntity.SHARDS;
@@ -40,6 +42,13 @@ public class TransportCatShardsAction extends HandledTransportAction<CatShardsRe
 
     private final NodeClient client;
     private final ResponseLimitSettings responseLimitSettings;
+    private static final IndicesStatsResponse EMPTY_INDICES_STATS_RESPONSE = new IndicesStatsResponse(
+        new ShardStats[0],
+        0,
+        0,
+        0,
+        Collections.emptyList()
+    );
 
     @Inject
     public TransportCatShardsAction(
@@ -108,6 +117,12 @@ 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(EMPTY_INDICES_STATS_RESPONSE);
+                            cancellableListener.onResponse(catShardsResponse);
+                            return;
+                        }
                         IndicesStatsRequest indicesStatsRequest = new IndicesStatsRequest();
                         indicesStatsRequest.setShouldCancelOnTimeout(true);
                         indicesStatsRequest.all();
@@ -159,4 +174,8 @@ private void validateRequestLimit(
             }
         }
     }
+
+    private boolean shouldSkipIndicesStatsRequest(ShardPaginationStrategy paginationStrategy) {
+        return Objects.nonNull(paginationStrategy) && paginationStrategy.getRequestedEntities().isEmpty();
+    }
 }

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

@@ -43,6 +43,7 @@
 import org.opensearch.action.admin.indices.stats.IndexStats;
 import org.opensearch.action.admin.indices.stats.IndicesStatsRequest;
 import org.opensearch.action.admin.indices.stats.IndicesStatsResponse;
+import org.opensearch.action.admin.indices.stats.ShardStats;
 import org.opensearch.action.pagination.IndexPaginationStrategy;
 import org.opensearch.action.pagination.PageToken;
 import org.opensearch.action.support.GroupedActionListener;
@@ -104,6 +105,14 @@ public class RestIndicesAction extends AbstractListAction {
         "Parameter [master_timeout] is deprecated and will be removed in 3.0. To support inclusive language, please use [cluster_manager_timeout] instead.";
     private static final String DUPLICATE_PARAMETER_ERROR_MESSAGE =
         "Please only use one of the request parameters [master_timeout, cluster_manager_timeout].";
+    private static final IndicesStatsResponse EMPTY_INDICES_STATS_RESPONSE = new IndicesStatsResponse(
+        new ShardStats[0],
+        0,
+        0,
+        0,
+        Collections.emptyList()
+    );
+    private static final ClusterHealthResponse EMPTY_CLUSTER_HEALTH_RESPONSE = new ClusterHealthResponse();
 
     private final ResponseLimitSettings responseLimitSettings;
 
@@ -212,6 +221,14 @@ public void onResponse(ClusterStateResponse clusterStateResponse) {
                                     groupedListener.onResponse(getSettingsResponse);
                                     groupedListener.onResponse(clusterStateResponse);
 
+                                    // For paginated queries, if strategy outputs no indices to be returned,
+                                    // avoid fetching health and stats.
+                                    if (shouldSkipNextRequests(paginationStrategy)) {
+                                        groupedListener.onResponse(EMPTY_CLUSTER_HEALTH_RESPONSE);
+                                        groupedListener.onResponse(EMPTY_INDICES_STATS_RESPONSE);
+                                        return;
+                                    }
+
                                     sendIndicesStatsRequest(
                                         indicesToBeQueried,
                                         subRequestIndicesOptions,
@@ -1093,4 +1110,8 @@ public Tuple<String, Settings> next() {
         };
     }
 
+    private boolean shouldSkipNextRequests(IndexPaginationStrategy paginationStrategy) {
+        return Objects.nonNull(paginationStrategy) && paginationStrategy.getRequestedEntities().isEmpty();
+    }
+
 }