Using HBase coprocessors
You can configure HBase coprocessors to run your own custom code. The HBase coprocessor framework provides a way to extend HBase with custom functionality. Coprocessors provide a way to run server-level code against locally-stored data.
Coprocessors are not designed to be used by end users of HBase, but by HBase developers who need to add specialized functionality to HBase. One example of the use of coprocessors is pluggable compaction and scan policies.