x86 sucks. (well, for accessing lots of memory) There's a patch (in -aa) to change the default kernel/user split to 0.5:3.5 GB, but the InnoDB manual states glibc is still buggy and the stack and heap can collide if you allocate more than 2GB. But perhaps the glibc they statically link is aware of mapping changes with the -aa patch? I'd hope.
So say I have a machine with 4GB. I can safely have the database address 2GB. Factor into 500+ connections, taking 2.25 MB each. Remove 20MB for Inno's dictionary pool and 30 MB for misc MyISAM table indices which can't run on Inno... Down to 738 MB for InnoDB's data/key cache. Out of 4GB. Pathetic. See why I want the DBI proxy and more address space?
Sure, the rest of the memory will be used somewhat-usefully by the kernel's buffer cache, but not ideally. The database could utilize it better.
Unfortunately I don't have a spare machine with 4GB of memory to tinker with. I have three with 2 GB in the closet, but they all have motherboards with 2 GB limits.
Actually, I guess I do have a spare machine, since LJ just got two new databases... Waiting for lisa to get them online, then I can play.