@Override
  public final void updateWeight(Map<Class<? extends CandidateGenerator>, Double> weights) {
    weights.merge(LoadCandidateGenerator.class, cost(), Double::sum);
  }
Compute the cost of a potential cluster state from skew in number of regions on a cluster.
hbase-balancer/src/main/java/org/apache/hadoop/hbase/master/balancer/RegionCountSkewCostFunction.java