Our parser cache hit ratio is very low, around 30%.
http://tstarling.com/stuff/hit-rate-2011-03-25.png
This seems to be mostly due to insufficient parser cache size. My
theory is that if we increased the parser cache size by a factor of
10-100, then most of the yellow area on that graph should go away.
This would reduce our apache CPU usage substantially.
The parser cache does not have particularly stringent latency
requirements, since most requests only do a single parser cache fetch.
So I researched the available options for disk-backed object caches.
Ehcache stood out, since it has a suitable feature set out of box and
was easy to use from PHP. I whipped up a MediaWiki client for it and
committed it in r83208.
My plan is to do a test deployment of it, starting on Monday my time
(i.e. Sunday night US time), and continuing until the cache fills up
somewhat, say 2 weeks. This deployment should have no user-visible
consequences, except perhaps for an improvement in speed.
-- Tim Starling
