Optimize cluster health request

server/src/main/java/org/elasticsearch/action/admin/cluster/health/TransportClusterHealthAction.java

@@ -31,6 +31,7 @@
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.inject.Inject;
 import org.elasticsearch.common.util.CollectionUtils;
+import org.elasticsearch.core.Nullable;
 import org.elasticsearch.core.TimeValue;
 import org.elasticsearch.index.IndexNotFoundException;
 import org.elasticsearch.node.NodeClosedException;
@@ -211,9 +212,9 @@ private void executeHealth(
             return;
         }
 
-        final Predicate<ClusterState> validationPredicate = newState -> validateRequest(request, newState, waitCount);
-        if (validationPredicate.test(currentState)) {
-            listener.onResponse(getResponse(request, currentState, waitCount, TimeoutState.OK));
+        ClusterHealthResponse validResponse = validateRequestAndGetResponse(request, currentState, waitCount);
+        if (validResponse != null) {
+            listener.onResponse(validResponse);
         } else {
             final ClusterStateObserver observer = new ClusterStateObserver(
                 currentState,
@@ -238,6 +239,7 @@ public void onTimeout(TimeValue timeout) {
                     listener.onResponse(getResponse(request, observer.setAndGetObservedState(), waitCount, TimeoutState.TIMED_OUT));
                 }
             };
+            Predicate<ClusterState> validationPredicate = newState -> validateRequest(request, newState, waitCount);
             observer.waitForNextChange(stateListener, validationPredicate, request.timeout());
         }
     }
@@ -276,6 +278,22 @@ private boolean validateRequest(final ClusterHealthRequest request, ClusterState
         return prepareResponse(request, response, clusterState, indexNameExpressionResolver) == waitCount;
     }
 
+    @Nullable
+    private ClusterHealthResponse validateRequestAndGetResponse(final ClusterHealthRequest request, ClusterState clusterState, final int waitCount) {
+        ClusterHealthResponse response = clusterHealth(
+            request,
+            clusterState,
+            clusterService.getMasterService().numberOfPendingTasks(),
+            allocationService.getNumberOfInFlightFetches(),
+            clusterService.getMasterService().getMaxTaskWaitTime()
+        );
+        if (prepareResponse(request, response, clusterState, indexNameExpressionResolver) == waitCount) {
+            return response;
+        } else {
+            return null;
+        }
+    }
+
     private enum TimeoutState {
         OK,
         TIMED_OUT,