public long cacheBlockHeapSize() {
      return LruCachedBlock.PER_BLOCK_OVERHEAD + ClassSize.align(cacheKey.heapSize())
        + ClassSize.align(size);
    }
Size of the cache block holding this item. Used for verification.
hbase-server/src/test/java/org/apache/hadoop/hbase/io/hfile/TestLruAdaptiveBlockCache.java