@Override
  public void incrementRegionSize(RegionInfo regionInfo, long delta) {
    if (LOG.isTraceEnabled()) {
      LOG.trace("Updating space quota size for " + regionInfo + " with a delta of " + delta);
    }
    // Atomic. Recomputes the stored value with the delta if there is one, otherwise use the delta.
    store.compute(regionInfo,
      (key, value) -> value == null ? new RegionSizeImpl(delta) : value.incrementSize(delta));
  }
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