(Tim Starling ts4294967296@hotmail.com): [Notes on caching]
When I recompiled Apache to add mod_mmap_static, I also updated PHP to 4.3, and compiled the latter with the shared memory functions. After we get things stable again, the first optimization I plan to try is to have a shared-memory cache of existing page titles, so we don't have to go to the database dozens of times per page render. I suspect that will gain us more than caching whole pages.
But for now, we're in rescue mode.