Speedup BalanceUnbalancedClusterTests (#88794)

This commit speeds up the above tests (and probably many others) by changing how
 we assert the invariant. Previously invariant was checked by rebuilding
 internal collections from scratch and comparing them against ones already
 present in the object after every single modification twice. This commit
 verifies the invariant once after all bulk changes.

server/src/main/java/org/elasticsearch/cluster/routing/RoutingNode.java

@@ -15,7 +15,6 @@
 import org.elasticsearch.index.shard.ShardId;
 
 import java.util.ArrayList;
-import java.util.Collection;
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.Iterator;
@@ -26,7 +25,6 @@
 import java.util.Objects;
 import java.util.Set;
 import java.util.function.Predicate;
-import java.util.stream.Collectors;
 
 /**
  * A {@link RoutingNode} represents a cluster node associated with a single {@link DiscoveryNode} including all shards
@@ -118,7 +116,14 @@ public int size() {
      * @param shard Shard to create on this Node
      */
     void add(ShardRouting shard) {
-        assert invariant();
+        addInternal(shard, true);
+    }
+
+    void addWithoutValidation(ShardRouting shard) {
+        addInternal(shard, false);
+    }
+
+    private void addInternal(ShardRouting shard, boolean validate) {
         final ShardRouting existing = shards.putIfAbsent(shard.shardId(), shard);
         if (existing != null) {
             final IllegalStateException e = new IllegalStateException(
@@ -142,11 +147,10 @@ void add(ShardRouting shard) {
             relocatingShards.add(shard);
         }
         shardsByIndex.computeIfAbsent(shard.index(), k -> new HashSet<>()).add(shard);
-        assert invariant();
+        assert validate == false || invariant();
     }
 
     void update(ShardRouting oldShard, ShardRouting newShard) {
-        assert invariant();
         if (shards.containsKey(oldShard.shardId()) == false) {
             // Shard was already removed by routing nodes iterator
             // TODO: change caller logic in RoutingNodes so that this check can go away
@@ -174,7 +178,6 @@ void update(ShardRouting oldShard, ShardRouting newShard) {
     }
 
     void remove(ShardRouting shard) {
-        assert invariant();
         ShardRouting previousValue = shards.remove(shard.shardId());
         assert previousValue == shard : "expected shard " + previousValue + " but was " + shard;
         if (shard.initializing()) {
@@ -342,20 +345,24 @@ public boolean isEmpty() {
         return shards.isEmpty();
     }
 
-    private boolean invariant() {
-        // initializingShards must consistent with that in shards
-        Collection<ShardRouting> shardRoutingsInitializing = shards.values().stream().filter(ShardRouting::initializing).toList();
-        assert initializingShards.size() == shardRoutingsInitializing.size();
-        assert initializingShards.containsAll(shardRoutingsInitializing);
+    boolean invariant() {
+        var shardRoutingsInitializing = new ArrayList<ShardRouting>(shards.size());
+        var shardRoutingsRelocating = new ArrayList<ShardRouting>(shards.size());
+        // this guess assumes 1 shard per index, this is not precise, but okay for assertion
+        var shardRoutingsByIndex = Maps.<Index, Set<ShardRouting>>newHashMapWithExpectedSize(shards.size());
 
-        // relocatingShards must consistent with that in shards
-        Collection<ShardRouting> shardRoutingsRelocating = shards.values().stream().filter(ShardRouting::relocating).toList();
-        assert relocatingShards.size() == shardRoutingsRelocating.size();
-        assert relocatingShards.containsAll(shardRoutingsRelocating);
+        for (var shard : shards.values()) {
+            if (shard.initializing()) {
+                shardRoutingsInitializing.add(shard);
+            }
+            if (shard.relocating()) {
+                shardRoutingsRelocating.add(shard);
+            }
+            shardRoutingsByIndex.computeIfAbsent(shard.index(), k -> new HashSet<>(10)).add(shard);
+        }
 
-        final Map<Index, Set<ShardRouting>> shardRoutingsByIndex = shards.values()
-            .stream()
-            .collect(Collectors.groupingBy(ShardRouting::index, Collectors.toSet()));
+        assert initializingShards.size() == shardRoutingsInitializing.size() && initializingShards.containsAll(shardRoutingsInitializing);
+        assert relocatingShards.size() == shardRoutingsRelocating.size() && relocatingShards.containsAll(shardRoutingsRelocating);
         assert shardRoutingsByIndex.equals(shardsByIndex);
 
         return true;

server/src/main/java/org/elasticsearch/cluster/routing/RoutingNodes.java

@@ -122,15 +122,16 @@ private RoutingNodes(RoutingTable routingTable, DiscoveryNodes discoveryNodes, b
                     // A replica Set might have one (and not more) replicas with the state of RELOCATING.
                     if (shard.assignedToNode()) {
                         // LinkedHashMap to preserve order
-                        nodesToShards.computeIfAbsent(shard.currentNodeId(), createRoutingNode).add(shard);
+                        nodesToShards.computeIfAbsent(shard.currentNodeId(), createRoutingNode).addWithoutValidation(shard);
                         assignedShardsAdd(shard);
                         if (shard.relocating()) {
                             relocatingShards++;
                             ShardRouting targetShardRouting = shard.getTargetRelocatingShard();
                             addInitialRecovery(targetShardRouting, indexShard.primary);
                             // LinkedHashMap to preserve order.
                             // Add the counterpart shard with relocatingNodeId reflecting the source from which it's relocating from.
-                            nodesToShards.computeIfAbsent(shard.relocatingNodeId(), createRoutingNode).add(targetShardRouting);
+                            nodesToShards.computeIfAbsent(shard.relocatingNodeId(), createRoutingNode)
+                                .addWithoutValidation(targetShardRouting);
                             assignedShardsAdd(targetShardRouting);
                         } else if (shard.initializing()) {
                             if (shard.primary()) {
@@ -145,6 +146,7 @@ private RoutingNodes(RoutingTable routingTable, DiscoveryNodes discoveryNodes, b
                 }
             }
         }
+        nodesToShards.values().forEach(RoutingNode::invariant);
     }
 
     private RoutingNodes(RoutingNodes routingNodes) {