@RestrictedApi(explanation = "Should only be called in tests", link = "",
      allowedOnPath = ".*/src/test/.*")
  void setRackManager(RackManager rackManager) {
    this.rackManager = rackManager;
  }
Select the candidate generator to use based on the cost of cost functions. The chance of
selecting a candidate generator is proportional to the share of cost of all cost functions
among all cost functions that benefit from it.
hbase-balancer/src/main/java/org/apache/hadoop/hbase/master/balancer/StochasticLoadBalancer.java