ClusterState has a bunch of methods such as getSlice and getReplica which internally call getCollectionOrNull that ends up making a call to ZK via the lazy collection reference. Many classes use these methods even though a DocCollection object is available. In such cases, multiple redundant calls to ZooKeeper can happen if the collection is not watched locally. This is especially true for Overseer classes which operate on all collections.
We should audit all usages of these methods and replace them with calls to appropriate DocCollection methods.