Optimizations for PHP and MySQL?

I was trying to setup a wiki on DH. I’ve played with WikkaWiki and MediaWiki. The WikkaWiki’s performance in somewhat acceptable but MediaWiki has been slow.

I’m guessing that the problem isn’t the speed of these apps but something on the servers. The MediaWiki is taking 5-6 seconds minimum to render a page.

Is there anything you can do to speed this up? I’m wondering what others are doing to optimize PHP and MySQL on DH.