@Override
  public boolean compareAndSetDataSize(long expected, long updated) {
    return dataSize.compareAndSet(expected, updated);
  }
Accounting of current heap and data sizes. Thread-safe. Many threads can do updates against this
single instance.
@see NonThreadSafeMemStoreSizing
@see MemStoreSize
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/ThreadSafeMemStoreSizing.java