Bypass the BlockCache

You can bypass the BlockCache if the data needed for a specific but atypical operation does not all fit in memory.

For an atypical operation does not all fit in memory, using the BlockCache can be counter-productive because data that you are still using may be evicted, or even if other data is not evicted, excess garbage collection can adversely effect performance. For this type of operation, you may decide to bypass the BlockCache. To bypass the BlockCache for a given Scan or Get, use the setCacheBlocks(false) method.

In addition, you can prevent a specific column family's contents from being cached, by setting its BLOCKCACHE configuration to false. Use the following syntax in HBase Shell:
hbase> alter 'myTable', CONFIGURATION => {NAME => 'myCF', BLOCKCACHE => 'false'}