(Answering an IRC question up here so Rong-en, the asker, sees response)
In the log it will say what kind of compaction it is, or explicitly it logs when its a 'major' compaction. Are the compactions you are seeing 'major' compactions? My guess is they are. Major compactions happen on a period (Default every 24 hours). But we don't persist the time of the last major compaction and I'm guessing that because we don't, every restart runs one. Can you confirm Rong-en? If this is the case, its a bug. Please file a JIRA. We need to fix it.
St.Ack
