ReactiveStorageDeciderService constructs a lot of RoutingNodes

[DaveCTurner]

Well ok it constructs two of them:

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

Line 194 in 095e49e

RoutingNodes routingNodes = new RoutingNodes(state, false);

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

Line 211 in 095e49e

RoutingNodes routingNodes = new RoutingNodes(state, false);

That's still quite a lot, these things are expensive to construct:

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

Lines 499 to 504 in 095e49e

	/**
	* Create a mutable {@link RoutingNodes}. This is a costly operation so this must only be called once!
	*/
	private RoutingNodes getMutableRoutingNodes(ClusterState clusterState) {
	return new RoutingNodes(clusterState, false);
	}

I don't think we need these things to be mutable, so why not use ClusterState#getRoutingNodes() instead?

[elasticmachine]

Pinging @elastic/es-distributed (Team:Distributed)

[henningandersen]

Thanks for raising this, David, this is a leftover from previous iterations where we did mutate the routing nodes.