Anything that improves our i/o profile makes hbase run smoother. Over in
HBASE-2457, good work has been done already describing the tension between minimizing compactions versus minimizing count of store files. This issue is about following on from what has been done in 2457 but also, breaking the hard-to-read compaction code out of Store.java out to a standalone class that can be the easier tested (and easily analyzed for its performance characteristics).
If possible, in the refactor, we'd allow specification of alternate merge sort implementations.