Small cleanups to Allocation Performance

server/src/main/java/org/elasticsearch/cluster/metadata/Metadata.java

@@ -1024,9 +1024,7 @@ public Map<String, DataStreamAlias> dataStreamAliases() {
     }
 
     public Map<String, SingleNodeShutdownMetadata> nodeShutdowns() {
-        return Optional.ofNullable((NodesShutdownMetadata) this.custom(NodesShutdownMetadata.TYPE))
-            .map(NodesShutdownMetadata::getAllNodeMetadataMap)
-            .orElse(Collections.emptyMap());
+        return this.custom(NodesShutdownMetadata.TYPE, NodesShutdownMetadata.EMPTY).getAllNodeMetadataMap();
     }
 
     public Map<String, Custom> customs() {

server/src/main/java/org/elasticsearch/cluster/metadata/NodesShutdownMetadata.java

@@ -22,7 +22,6 @@
 import org.elasticsearch.xcontent.XContentParser;
 
 import java.io.IOException;
-import java.util.Collections;
 import java.util.EnumSet;
 import java.util.HashMap;
 import java.util.List;
@@ -93,11 +92,11 @@ public static NodesShutdownMetadata getShutdownsOrEmpty(final ClusterState state
     private final Map<String, SingleNodeShutdownMetadata> nodes;
 
     public NodesShutdownMetadata(Map<String, SingleNodeShutdownMetadata> nodes) {
-        this.nodes = Collections.unmodifiableMap(nodes);
+        this.nodes = Map.copyOf(nodes);
     }
 
     public NodesShutdownMetadata(StreamInput in) throws IOException {
-        this(in.readMap(StreamInput::readString, SingleNodeShutdownMetadata::new));
+        this(in.readImmutableMap(StreamInput::readString, SingleNodeShutdownMetadata::new));
     }
 
     @Override

server/src/main/java/org/elasticsearch/cluster/routing/allocation/RoutingAllocation.java

@@ -26,7 +26,6 @@
 import org.elasticsearch.snapshots.RestoreService.RestoreInProgressUpdater;
 import org.elasticsearch.snapshots.SnapshotShardSizeInfo;
 
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Map;
@@ -73,6 +72,11 @@ public class RoutingAllocation {
 
     private final Map<String, SingleNodeShutdownMetadata> nodeReplacementTargets;
 
+    private final Map<String, SingleNodeShutdownMetadata> nodeShutdowns;
+
+    @Nullable
+    private final DesiredNodes desiredNodes;
+
     public RoutingAllocation(
         AllocationDeciders deciders,
         ClusterState clusterState,
@@ -106,13 +110,15 @@ public RoutingAllocation(
         this.clusterInfo = clusterInfo;
         this.shardSizeInfo = shardSizeInfo;
         this.currentNanoTime = currentNanoTime;
+        this.nodeShutdowns = clusterState.metadata().nodeShutdowns();
         Map<String, SingleNodeShutdownMetadata> targetNameToShutdown = new HashMap<>();
-        for (SingleNodeShutdownMetadata shutdown : clusterState.metadata().nodeShutdowns().values()) {
+        for (SingleNodeShutdownMetadata shutdown : nodeShutdowns.values()) {
             if (shutdown.getType() == SingleNodeShutdownMetadata.Type.REPLACE) {
                 targetNameToShutdown.put(shutdown.getTargetNodeName(), shutdown);
             }
         }
-        this.nodeReplacementTargets = Collections.unmodifiableMap(targetNameToShutdown);
+        this.nodeReplacementTargets = Map.copyOf(targetNameToShutdown);
+        this.desiredNodes = DesiredNodes.latestFromClusterState(clusterState);
     }
 
     /** returns the nano time captured at the beginning of the allocation. used to make sure all time based decisions are aligned */
@@ -173,14 +179,14 @@ public SnapshotShardSizeInfo snapshotShardSizeInfo() {
 
     @Nullable
     public DesiredNodes desiredNodes() {
-        return DesiredNodes.latestFromClusterState(clusterState);
+        return desiredNodes;
     }
 
     /**
      * Returns the map of node id to shutdown metadata currently in the cluster
      */
     public Map<String, SingleNodeShutdownMetadata> nodeShutdowns() {
-        return metadata().nodeShutdowns();
+        return nodeShutdowns;
     }
 
     /**

server/src/main/java/org/elasticsearch/cluster/routing/allocation/decider/NodeShutdownAllocationDecider.java

@@ -9,14 +9,11 @@
 package org.elasticsearch.cluster.routing.allocation.decider;
 
 import org.elasticsearch.cluster.metadata.IndexMetadata;
-import org.elasticsearch.cluster.metadata.Metadata;
-import org.elasticsearch.cluster.metadata.NodesShutdownMetadata;
 import org.elasticsearch.cluster.metadata.SingleNodeShutdownMetadata;
 import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.cluster.routing.RoutingNode;
 import org.elasticsearch.cluster.routing.ShardRouting;
 import org.elasticsearch.cluster.routing.allocation.RoutingAllocation;
-import org.elasticsearch.core.Nullable;
 
 /**
  * An allocation decider that prevents shards from being allocated to a
@@ -35,7 +32,7 @@ public class NodeShutdownAllocationDecider extends AllocationDecider {
      */
     @Override
     public Decision canAllocate(ShardRouting shardRouting, RoutingNode node, RoutingAllocation allocation) {
-        final SingleNodeShutdownMetadata thisNodeShutdownMetadata = getNodeShutdownMetadata(allocation.metadata(), node.nodeId());
+        final SingleNodeShutdownMetadata thisNodeShutdownMetadata = allocation.nodeShutdowns().get(node.nodeId());
 
         if (thisNodeShutdownMetadata == null) {
             // There's no shutdown metadata for this node, return yes.
@@ -73,7 +70,7 @@ public Decision canRemain(IndexMetadata indexMetadata, ShardRouting shardRouting
      */
     @Override
     public Decision shouldAutoExpandToNode(IndexMetadata indexMetadata, DiscoveryNode node, RoutingAllocation allocation) {
-        SingleNodeShutdownMetadata thisNodeShutdownMetadata = getNodeShutdownMetadata(allocation.metadata(), node.getId());
+        SingleNodeShutdownMetadata thisNodeShutdownMetadata = allocation.nodeShutdowns().get(node.getId());
 
         if (thisNodeShutdownMetadata == null) {
             return allocation.decision(Decision.YES, NAME, "node [%s] is not preparing for removal from the cluster", node.getId());
@@ -95,14 +92,4 @@ public Decision shouldAutoExpandToNode(IndexMetadata indexMetadata, DiscoveryNod
         };
     }
 
-    @Nullable
-    private static SingleNodeShutdownMetadata getNodeShutdownMetadata(Metadata metadata, String nodeId) {
-        NodesShutdownMetadata nodesShutdownMetadata = metadata.custom(NodesShutdownMetadata.TYPE);
-        if (nodesShutdownMetadata == null || nodesShutdownMetadata.getAllNodeMetadataMap() == null) {
-            // There are no nodes in the process of shutting down, return null.
-            return null;
-        }
-
-        return nodesShutdownMetadata.getAllNodeMetadataMap().get(nodeId);
-    }
 }