Make ClusterInfo use immutable maps in all cases (#88447)

This class's maps are used very hot in the disk threshold allocation
decider. Moving them from hppc maps to unmodifiable map wrapping
`HashMap` has led to a measurable slowdown in the many-shards benchmark
bootstrapping. Lets use immutable map copies here exclusively to make
performance outright better and more predictable via a single implementation.

server/src/main/java/org/elasticsearch/cluster/ClusterInfo.java

@@ -68,12 +68,12 @@ public ClusterInfo(
         Map<ShardRouting, String> routingToDataPath,
         Map<NodeAndPath, ReservedSpace> reservedSpace
     ) {
-        this.leastAvailableSpaceUsage = leastAvailableSpaceUsage;
-        this.shardSizes = shardSizes;
-        this.shardDataSetSizes = shardDataSetSizes;
-        this.mostAvailableSpaceUsage = mostAvailableSpaceUsage;
-        this.routingToDataPath = routingToDataPath;
-        this.reservedSpace = reservedSpace;
+        this.leastAvailableSpaceUsage = Map.copyOf(leastAvailableSpaceUsage);
+        this.shardSizes = Map.copyOf(shardSizes);
+        this.shardDataSetSizes = Map.copyOf(shardDataSetSizes);
+        this.mostAvailableSpaceUsage = Map.copyOf(mostAvailableSpaceUsage);
+        this.routingToDataPath = Map.copyOf(routingToDataPath);
+        this.reservedSpace = Map.copyOf(reservedSpace);
     }
 
     public ClusterInfo(StreamInput in) throws IOException {

server/src/main/java/org/elasticsearch/cluster/InternalClusterInfoService.java

@@ -39,7 +39,6 @@
 import org.elasticsearch.threadpool.ThreadPool;
 
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
@@ -188,8 +187,8 @@ public void onResponse(NodesStatsResponse nodesStatsResponse) {
                         leastAvailableUsagesBuilder,
                         mostAvailableUsagesBuilder
                     );
-                    leastAvailableSpaceUsages = Collections.unmodifiableMap(leastAvailableUsagesBuilder);
-                    mostAvailableSpaceUsages = Collections.unmodifiableMap(mostAvailableUsagesBuilder);
+                    leastAvailableSpaceUsages = Map.copyOf(leastAvailableUsagesBuilder);
+                    mostAvailableSpaceUsages = Map.copyOf(mostAvailableUsagesBuilder);
                 }
 
                 @Override
@@ -262,10 +261,10 @@ public void onResponse(IndicesStatsResponse indicesStatsResponse) {
                     reservedSpaceBuilders.forEach((nodeAndPath, builder) -> rsrvdSpace.put(nodeAndPath, builder.build()));
 
                     indicesStatsSummary = new IndicesStatsSummary(
-                        Collections.unmodifiableMap(shardSizeByIdentifierBuilder),
-                        Collections.unmodifiableMap(shardDataSetSizeBuilder),
-                        Collections.unmodifiableMap(dataPathByShardRoutingBuilder),
-                        Collections.unmodifiableMap(rsrvdSpace)
+                        Map.copyOf(shardSizeByIdentifierBuilder),
+                        Map.copyOf(shardDataSetSizeBuilder),
+                        Map.copyOf(dataPathByShardRoutingBuilder),
+                        Map.copyOf(rsrvdSpace)
                     );
                 }
 

server/src/test/java/org/elasticsearch/cluster/routing/allocation/DiskThresholdMonitorTests.java

@@ -964,7 +964,7 @@ private static ClusterInfo clusterInfo(
         Map<String, DiskUsage> diskUsages,
         Map<ClusterInfo.NodeAndPath, ClusterInfo.ReservedSpace> reservedSpace
     ) {
-        return new ClusterInfo(diskUsages, null, null, null, null, reservedSpace);
+        return new ClusterInfo(diskUsages, Map.of(), Map.of(), Map.of(), Map.of(), reservedSpace);
     }
 
     private static DiscoveryNode newFrozenOnlyNode(String nodeId) {

server/src/test/java/org/elasticsearch/cluster/routing/allocation/decider/DiskThresholdDeciderTests.java

@@ -1308,7 +1308,7 @@ static class DevNullClusterInfo extends ClusterInfo {
             Map<String, Long> shardSizes,
             Map<NodeAndPath, ReservedSpace> reservedSpace
         ) {
-            super(leastAvailableSpaceUsage, mostAvailableSpaceUsage, shardSizes, null, null, reservedSpace);
+            super(leastAvailableSpaceUsage, mostAvailableSpaceUsage, shardSizes, Map.of(), Map.of(), reservedSpace);
         }
 
         @Override

server/src/test/java/org/elasticsearch/cluster/routing/allocation/decider/DiskThresholdDeciderUnitTests.java

@@ -107,7 +107,7 @@ public void testCanAllocateUsesMaxAvailableSpace() {
             leastAvailableUsages,
             mostAvailableUsage,
             Map.of("[test][0][p]", 10L), // 10 bytes,
-            null,
+            Map.of(),
             Map.of(),
             Map.of()
         );
@@ -185,7 +185,7 @@ public void testCannotAllocateDueToLackOfDiskResources() {
             leastAvailableUsages,
             mostAvailableUsage,
             Map.of("[test][0][p]", shardSize),
-            null,
+            Map.of(),
             Map.of(),
             Map.of()
         );
@@ -307,7 +307,7 @@ public void testCanRemainUsesLeastAvailableSpace() {
             leastAvailableUsages,
             mostAvailableUsage,
             shardSizes,
-            null,
+            Map.of(),
             shardRoutingMap,
             Map.of()
         );
@@ -745,7 +745,7 @@ public void testDecidesYesIfWatermarksIgnored() {
             allFullUsages,
             allFullUsages,
             Map.of("[test][0][p]", 10L),
-            null,
+            Map.of(),
             Map.of(),
             Map.of()
         );
@@ -815,7 +815,7 @@ public void testCannotForceAllocateOver100PercentUsage() {
         // bigger than available space
         final long shardSize = randomIntBetween(1, 10);
         shardSizes.put("[test][0][p]", shardSize);
-        ClusterInfo clusterInfo = new ClusterInfo(leastAvailableUsages, mostAvailableUsage, shardSizes, null, Map.of(), Map.of());
+        ClusterInfo clusterInfo = new ClusterInfo(leastAvailableUsages, mostAvailableUsage, shardSizes, Map.of(), Map.of(), Map.of());
         RoutingAllocation allocation = new RoutingAllocation(
             new AllocationDeciders(Collections.singleton(decider)),
             clusterState,

x-pack/plugin/autoscaling/src/main/java/org/elasticsearch/xpack/autoscaling/storage/ReactiveStorageDeciderService.java

@@ -793,7 +793,14 @@ private static class ExtendedClusterInfo extends ClusterInfo {
             private final ClusterInfo delegate;
 
             private ExtendedClusterInfo(Map<String, Long> extraShardSizes, ClusterInfo info) {
-                super(info.getNodeLeastAvailableDiskUsages(), info.getNodeMostAvailableDiskUsages(), extraShardSizes, Map.of(), null, null);
+                super(
+                    info.getNodeLeastAvailableDiskUsages(),
+                    info.getNodeMostAvailableDiskUsages(),
+                    extraShardSizes,
+                    Map.of(),
+                    Map.of(),
+                    Map.of()
+                );
                 this.delegate = info;
             }
 

x-pack/plugin/autoscaling/src/test/java/org/elasticsearch/xpack/autoscaling/capacity/AutoscalingCalculateCapacityServiceTests.java

@@ -260,7 +260,7 @@ public void testContext() {
             }
         }
         state = ClusterState.builder(ClusterName.DEFAULT).nodes(nodes).build();
-        info = new ClusterInfo(leastUsages, mostUsages, null, null, null, null);
+        info = new ClusterInfo(leastUsages, mostUsages, Map.of(), Map.of(), Map.of(), Map.of());
         context = new AutoscalingCalculateCapacityService.DefaultAutoscalingDeciderContext(
             roleNames,
             state,
@@ -306,7 +306,7 @@ public void testContext() {
                 )
             );
 
-            info = new ClusterInfo(leastUsages, mostUsages, null, null, null, null);
+            info = new ClusterInfo(leastUsages, mostUsages, Map.of(), Map.of(), Map.of(), Map.of());
             context = new AutoscalingCalculateCapacityService.DefaultAutoscalingDeciderContext(
                 roleNames,
                 state,

x-pack/plugin/autoscaling/src/test/java/org/elasticsearch/xpack/autoscaling/storage/FrozenStorageDeciderServiceTests.java

@@ -109,7 +109,7 @@ public Tuple<Long, ClusterInfo> sizeAndClusterInfo(IndexMetadata indexMetadata)
             // add irrelevant shards noise for completeness (should not happen IRL).
             sizes.put(new ShardId(index, i), randomLongBetween(0, Integer.MAX_VALUE));
         }
-        ClusterInfo info = new ClusterInfo(null, null, null, sizes, null, null);
+        ClusterInfo info = new ClusterInfo(Map.of(), Map.of(), Map.of(), sizes, Map.of(), Map.of());
         return Tuple.tuple(totalSize, info);
     }
 }

x-pack/plugin/autoscaling/src/test/java/org/elasticsearch/xpack/autoscaling/storage/ReactiveStorageDeciderServiceTests.java

@@ -403,7 +403,7 @@ public void validateSizeOf(ClusterState clusterState, ShardRouting subjectShard,
     }
 
     private ReactiveStorageDeciderService.AllocationState createAllocationState(Map<String, Long> shardSize, ClusterState clusterState) {
-        ClusterInfo info = new ClusterInfo(null, null, shardSize, null, null, null);
+        ClusterInfo info = new ClusterInfo(Map.of(), Map.of(), shardSize, Map.of(), Map.of(), Map.of());
         ReactiveStorageDeciderService.AllocationState allocationState = new ReactiveStorageDeciderService.AllocationState(
             clusterState,
             null,
@@ -567,7 +567,7 @@ public void testUnmovableSize() {
         if (shardsWithSizes.isEmpty() == false) {
             shardSize.put(shardIdentifier(randomFrom(shardsWithSizes)), ByteSizeUnit.KB.toBytes(minShardSize));
         }
-        ClusterInfo info = new ClusterInfo(diskUsages, diskUsages, shardSize, null, null, null);
+        ClusterInfo info = new ClusterInfo(diskUsages, diskUsages, shardSize, Map.of(), Map.of(), Map.of());
 
         ReactiveStorageDeciderService.AllocationState allocationState = new ReactiveStorageDeciderService.AllocationState(
             clusterState,