@Override
  public RegionSize getRegionSize(RegionInfo regionInfo) {
    return store.get(regionInfo);
  }
A {@link RegionSizeStore} implementation backed by a ConcurrentHashMap. We expected similar
amounts of reads and writes to the "store", so using a RWLock is not going to provide any
exceptional gains.
hbase-server/src/main/java/org/apache/hadoop/hbase/quotas/RegionSizeStoreImpl.java