Since upgrading to version 4.5.9 I've been seeing spikes in the load, sometimes reaching 18, for 10 minute periods. It causes users to come to my desk asking "what is wrong with Zimbra?", "why can't I log into my email?".
In top, i see mysql and java dancing around at the top, sometimes with zmlogger thrown into the mix. Looking at myslow.log and logger_myslow.log, i mainly see 0 and 1 times with a few numbers less than 21 thrown in.
We only began experiencing these issues after the 4.5.9 upgrade and I do not believe that our usage patterns have changed.