@Override
  public void put(RegionInfo regionInfo, long size) {
    if (LOG.isTraceEnabled()) {
      LOG.trace("Setting space quota size for " + regionInfo + " to " + size);
    }
    // Atomic. Either sets the new size for the first time, or replaces the existing value.
    store.compute(regionInfo,
      (key, value) -> value == null ? new RegionSizeImpl(size) : value.setSize(size));
  }
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