@Override
  public long getOldWALsDirSize() {
    if (master == null || !master.isInitialized()) {
      return 0;
    }
    return master.getMasterWalManager().getOldWALsDirSize();
  }
Impl for exposing HMaster Information through JMX
hbase-server/src/main/java/org/apache/hadoop/hbase/master/MetricsMasterWrapperImpl.java