About the Off-heap BucketCache

If the BucketCache is enabled, it stores data blocks, leaving the on-heap cache free for storing indexes and Bloom filters.

The physical location of the BucketCache storage can be either in memory (off-heap) or in a file stored in a fast disk.
  • Off-heap: This is the default configuration.
  • File-based: You can use the file-based storage mode to store the BucketCache on an SSD or FusionIO device,
You can configure a column family to keep its data blocks in the L1 cache instead of the BucketCache, using the HColumnDescriptor.cacheDataInL1(true) method or by using the following syntax in HBase Shell:
hbase> alter 'myTable', CONFIGURATION => {CACHE_DATA_IN_L1 => 'true'}}