@Override
  public void updateMetricsSize(int size) {
    if (size > 0) {
      metricsSize = size;
      mruCap = calcMruCap(size);
    }
  }
Calculates the mru cache capacity from the metrics size
hbase-hadoop-compat/src/main/java/org/apache/hadoop/hbase/master/balancer/MetricsStochasticBalancerSourceImpl.java