UPDATE: The info in this post is deprecated. See the new post about eAccelerator instead.
I installed Turck MMCache PHP accelerator and I got a big improvement.
ApacheBench reported 4.52 pages per second before and 12.47 pages after installation (a WordPress 1.5.2 page on a 1.2Ghz PIII). That a 275% increase in performance, with currently no observed problems. I tested this with both Apache2 and lighttpd, and got a similar boost with both.
There is only a package for Debian unstable at the moment, so I downloaded the package source and backported it to Debian sarge. I put the package in my apt repository (along with a backported openswan package I’m using). Add to your sources.list:
apt-get update ; apt-get install turck-mmcache
See PHP fly (comparatively)
UPDATE: I’m running into a few problems now actually. WordPress runs fine, but an application of my own is having some serious problems. MMTurck is kicking out the following log message:
I’ve disabled the extension for now until I investigate further.