During the month of May there was a spike in the amount of busy apache slots. What could have caused this spike?
If you look at Google Analytics (included below) there isn't really a change of traffic during May.
I also included the mysql graph to show that I enabled mysql caching at one point but I doubt it would cause more busy apache process.
Question
- What could have caused this busy server spike?
Stats
- Apache process: http://i.imgur.com/cMthh.png
- Mysql: http://i.imgur.com/vg6fj.png
- Google Analytics: http://i.imgur.com/yl8Ui.png
Google Analytics doesn't include traffic from web spiders, which is the likely source of your additional traffic. I'd recommend that you checkout out your crawl statistics using Google's Webmaster Tools. It (obviously) will only show you traffic generated by GoogleBot, but might offer a bit of insight.