@Override
    public long getDataHitCount() {
      return lruCacheStats.getDataHitCount() + bucketCacheStats.getDataHitCount();
    }
CombinedBlockCache is an abstraction layer that combines {@link FirstLevelBlockCache} and
{@link BucketCache}. The smaller lruCache is used to cache bloom blocks and index blocks. The
larger Cache is used to cache data blocks.
{@link #getBlock(BlockCacheKey, boolean, boolean, boolean)} reads first from the smaller l1Cache
before looking for the block in the l2Cache. Blocks evicted from l1Cache are put into the bucket
cache. Metrics are the combined size and hits and misses of both caches.
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/CombinedBlockCache.java