@Override
  public long heapSize() {
    return getCurrentSize();
  }
Creates a block cache.
@param maximumSizeInBytes maximum size of this cache, in bytes
@param avgBlockSize       expected average size of blocks, in bytes
@param maxBlockSize       maximum size of a block, in bytes
@param executor           the cache's executor
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/TinyLfuBlockCache.java