@Override
    public final void updateWeight(Map<Class<? extends CandidateGenerator>, Double> weights) {
      weights.merge(LoadCandidateGenerator.class, cost(), Double::sum);
    }
Collect the amount of region cached for all the regions from all the active region servers.
hbase-balancer/src/main/java/org/apache/hadoop/hbase/master/balancer/CacheAwareLoadBalancer.java