Prune unnecessary information from TransportNodesInfoAction.NodeInfoR…

…equest (elastic#99938)

There's no need to include the whole top-level `NodesInfoRequest` in the
requests for info from individual nodes, and this can add substantial
overhead if there are lots of nodes in the cluster. With this commit we
drop the wrapper in favour of just the parts of the top-level request
needed for the node-level processing.

Relates elastic#99744

docs/changelog/99938.yaml

@@ -0,0 +1,5 @@
+pr: 99938
+summary: "Prune unnecessary information from TransportNodesInfoAction.NodeInfoRequest"
+area: Stats
+type: enhancement
+issues: [99744]

server/src/main/java/org/elasticsearch/TransportVersions.java

@@ -150,6 +150,7 @@ static TransportVersion def(int id) {
     public static final TransportVersion ML_TRAINED_MODEL_CONFIG_PLATFORM_ADDED = def(8_507_00_0);
     public static final TransportVersion LONG_COUNT_IN_HISTOGRAM_ADDED = def(8_508_00_0);
     public static final TransportVersion INFERENCE_MODEL_SECRETS_ADDED = def(8_509_00_0);
+    public static final TransportVersion NODE_INFO_REQUEST_SIMPLIFIED = def(8_510_00_0);
     /*
      * STOP! READ THIS FIRST! No, really,
      *        ____ _____ ___  ____  _        ____  _____    _    ____    _____ _   _ ___ ____    _____ ___ ____  ____ _____ _

server/src/main/java/org/elasticsearch/action/admin/cluster/node/info/NodesInfoRequest.java

@@ -85,6 +85,13 @@ public NodesInfoRequest addMetric(String metric) {
      */
     public NodesInfoRequest addMetrics(String... metrics) {
         SortedSet<String> metricsSet = new TreeSet<>(Set.of(metrics));
+        return addMetrics(metricsSet);
+    }
+
+    /**
+     * Add multiple metrics
+     */
+    public NodesInfoRequest addMetrics(Set<String> metricsSet) {
         if (NodesInfoMetrics.Metric.allMetrics().containsAll(metricsSet) == false) {
             metricsSet.removeAll(NodesInfoMetrics.Metric.allMetrics());
             String plural = metricsSet.size() == 1 ? "" : "s";

server/src/main/java/org/elasticsearch/action/admin/cluster/node/info/TransportNodesInfoAction.java

@@ -26,6 +26,8 @@
 import java.util.List;
 import java.util.Set;
 
+import static org.elasticsearch.TransportVersions.NODE_INFO_REQUEST_SIMPLIFIED;
+
 public class TransportNodesInfoAction extends TransportNodesAction<
     NodesInfoRequest,
     NodesInfoResponse,
@@ -76,8 +78,7 @@ protected NodeInfo newNodeResponse(StreamInput in, DiscoveryNode node) throws IO
 
     @Override
     protected NodeInfo nodeOperation(NodeInfoRequest nodeRequest, Task task) {
-        NodesInfoRequest request = nodeRequest.request;
-        Set<String> metrics = request.requestedMetrics();
+        Set<String> metrics = nodeRequest.requestedMetrics();
         return nodeService.info(
             metrics.contains(NodesInfoMetrics.Metric.SETTINGS.metricName()),
             metrics.contains(NodesInfoMetrics.Metric.OS.metricName()),
@@ -96,21 +97,33 @@ protected NodeInfo nodeOperation(NodeInfoRequest nodeRequest, Task task) {
 
     public static class NodeInfoRequest extends TransportRequest {
 
-        NodesInfoRequest request;
+        private NodesInfoMetrics nodesInfoMetrics;
 
         public NodeInfoRequest(StreamInput in) throws IOException {
             super(in);
-            request = new NodesInfoRequest(in);
+            if (in.getTransportVersion().onOrAfter(NODE_INFO_REQUEST_SIMPLIFIED)) {
+                this.nodesInfoMetrics = new NodesInfoMetrics(in);
+            } else {
+                this.nodesInfoMetrics = new NodesInfoRequest(in).getNodesInfoMetrics();
+            }
         }
 
         public NodeInfoRequest(NodesInfoRequest request) {
-            this.request = request;
+            this.nodesInfoMetrics = request.getNodesInfoMetrics();
         }
 
         @Override
         public void writeTo(StreamOutput out) throws IOException {
             super.writeTo(out);
-            request.writeTo(out);
+            if (out.getTransportVersion().onOrAfter(NODE_INFO_REQUEST_SIMPLIFIED)) {
+                this.nodesInfoMetrics.writeTo(out);
+            } else {
+                new NodesInfoRequest().clear().addMetrics(nodesInfoMetrics.requestedMetrics()).writeTo(out);
+            }
+        }
+
+        public Set<String> requestedMetrics() {
+            return nodesInfoMetrics.requestedMetrics();
         }
     }
 }