You can use BlockCache compression, when you have more data than RAM allocated to BlockCache, but your compressed data can fit into BlockCache. The savings must be worth the increased garbage collection overhead and overall CPU load.
BlockCache compression caches data and encoded data blocks in their on-disk formats, rather than decompressing and decrypting them before caching. When compression is enabled on a column family, more data can fit into the amount of memory dedicated to BlockCache. Decompression is repeated every time a block is accessed, but the increase in available cache space can have a positive impact on throughput and mean latency.
If your data can fit into block cache without compression, or if your workload is sensitive to extra CPU or garbage collection overhead, we recommend against enabling BlockCache compression.
Block cache compression is disabled by default.
Before you can use BlockCache compression on an HBase table, compression must be enabled for the table. For more information, see Enable Compression on a ColumnFamily on the Apache website.