5be64ce4_Apache_HBase___Reference_Guide__Description
[Parameter] hbase.regionserver.thread.compaction.throttle [Default] 2 x hbase.hstore.compaction.max x hbase.hregion.memstore.flush.size (which defaults to 128) [Description] 
There are two different thread pools for compactions, one for large compactions and the other for small compactions. This helps to keep compaction of lean tables (such as hbase:meta) fast. If a compaction is larger than this threshold, it goes into the large compaction pool. In most cases, the default value is appropriate.
Apache HBase ™ Reference Guide
Description