We just posted a nice user- [1] and dev-view [2] on the "Accordion", the In-Memory Compaction feature that is coming in hbase-2.0.0 written by our Sisters and Brother at Yahoo! Research.
Check 'em out, St.Ack 1. https://blogs.apache.org/hbase/entry/accordion-hbase-breathes-with-in 2. https://blogs.apache.org/hbase/entry/accordion-developer-view-of-in