As a followup to this post, about my debate with MySQL support, they got back to me saying yes, after all, MySQL processes on 32-bit machines can go beyond 2.5GB. Here’s their response:
Hi!
Yes, you are right. In HIGHMEM mode, a process can go theoretically to 3 Gb.
If you have seen 3 Gb, then it was truly on the edge and you got quite lucky.
In HUGEMEM model, it can go up to 4 Gb per process. But performance penalty for CPU-intensive tasks is huge.
Yes, we experimented with PAE and found out that speed penalty for it is MUCH greater. Performance is actually dissapointing. We do have PAE working on Windows with InnoDB buffer pool, but it is recommended only for installation which are extremely disk bound.
And, yes, the best solution is 64-bit system. We had MySQL running with 16 or 32 Gb allocated to it, just fine.
We’ve been trouble-free now for 4 days since some tweaks made by our sysadmin, but it looks like we’re all in agreement that 64-bit is the way to go.