Remove unnecessary shuffle in unassigned shards allocation. (#65172)

Shuffling to avoid poisonous shards no longer has any
effect, since we always sort unassigned shards before
iterating them for allocation.

Author: howardhuanghua

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

@@ -18,7 +18,6 @@
 import org.elasticsearch.cluster.routing.UnassignedInfo.AllocationStatus;
 import org.elasticsearch.cluster.routing.allocation.ExistingShardsAllocator;
 import org.elasticsearch.cluster.service.MasterService;
-import org.elasticsearch.common.Randomness;
 import org.elasticsearch.core.Nullable;
 import org.elasticsearch.core.Tuple;
 import org.elasticsearch.index.Index;
@@ -1068,11 +1067,6 @@ public boolean isIgnoredEmpty() {
             return ignored.isEmpty();
         }
 
-        public void shuffle() {
-            nodes.ensureMutable();
-            Randomness.shuffle(unassigned);
-        }
-
         /**
          * Drains all unassigned shards and returns it.
          * This method will not drain ignored shards.

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

@@ -117,8 +117,6 @@ public ClusterState applyStartedShards(ClusterState clusterState, List<ShardRout
             return clusterState;
         }
         RoutingNodes routingNodes = getMutableRoutingNodes(clusterState);
-        // shuffle the unassigned shards, just so we won't have things like poison failed shards
-        routingNodes.unassigned().shuffle();
         RoutingAllocation allocation = new RoutingAllocation(
             allocationDeciders,
             routingNodes,
@@ -197,8 +195,6 @@ public ClusterState applyFailedShards(
         ClusterState tmpState = IndexMetadataUpdater.removeStaleIdsWithoutRoutings(clusterState, staleShards, logger);
 
         RoutingNodes routingNodes = getMutableRoutingNodes(tmpState);
-        // shuffle the unassigned shards, just so we won't have things like poison failed shards
-        routingNodes.unassigned().shuffle();
         long currentNanoTime = currentNanoTime();
         RoutingAllocation allocation = new RoutingAllocation(
             allocationDeciders,
@@ -274,8 +270,6 @@ public ClusterState applyFailedShards(
      */
     public ClusterState disassociateDeadNodes(ClusterState clusterState, boolean reroute, String reason) {
         RoutingNodes routingNodes = getMutableRoutingNodes(clusterState);
-        // shuffle the unassigned shards, just so we won't have things like poison failed shards
-        routingNodes.unassigned().shuffle();
         RoutingAllocation allocation = new RoutingAllocation(
             allocationDeciders,
             routingNodes,
@@ -479,8 +473,6 @@ public ClusterState reroute(ClusterState clusterState, String reason) {
         ClusterState fixedClusterState = adaptAutoExpandReplicas(clusterState);
 
         RoutingNodes routingNodes = getMutableRoutingNodes(fixedClusterState);
-        // shuffle the unassigned shards, just so we won't have things like poison failed shards
-        routingNodes.unassigned().shuffle();
         RoutingAllocation allocation = new RoutingAllocation(
             allocationDeciders,
             routingNodes,