I've got a query that's stalling, and I have no idea why. It looks sensible, but it runs "forever" (I went and had my lunch and left it running, hadn't finished 20 mins later).
Looking at "SHOW PROCESSLIST", I see my connection has the status "Copying to tmp table".
I looked in my my.cnf, and it looks like temp files should be in /tmp, but there's nothing relating to MySQL in there (there's only 2 directories, both empty).
To help me diagnose what was wrong, I thought I'd have a look at the temporary file it was supposedly copying to. If it was huge, I must have messed up a query. If not, perhaps it's a bug.
But I can't figure out where it's storing them. Is it an in-memory "file"?
I'm running MySQL 5.1.31 on a Ubuntu 9.04 JeOS install.