Provides implementations of HFile and HFile BlockCache. Caches are configured (and instantiated) by CacheConfig. See head of the CacheConfig class for constants that define cache options and configuration keys to use setting cache options. Cache implementations include the default, native on-heap LruBlockCache and a BucketCache that has a bunch of deploy formats including acting as a L2 for LruBlockCache -- when a block is evicted from LruBlockCache, it goes to the BucketCache and when we search a block, we look in both places -- or, the most common deploy type, using CombinedBlockCache, BucketCache is used as a host for data blocks with meta blocks in an instance of LruBlockCache. BucketCache can also be onheap, offheap, and file-backed.

Which BlockCache should I use?

By default LruBlockCache is on. If you would like to cache more, and offheap (offheap usually means less GC headache), try enabling * BucketCache. Fetching will always be slower when fetching from BucketCache but latencies tend to be less erratic over time (roughly because GC is less). See Nick Dimiduk's BlockCache 101 for some numbers.

Enabling BucketCache

See the HBase Reference Guide Enable BucketCache.