On Thu, 2006-12-07 at 19:44 -0500, Tom Lane wrote: > Jeff Davis <pgsql@xxxxxxxxxxx> writes: > > I don't understand. CREATE INDEX CONCURRENTLY can't be run in a > > transaction block anyway, so a REINDEX CONCURRENTLY wouldn't either. So > > how (or when) would you deadlock? > > The problem is you need to upgrade from a nonexclusive table lock to an > exclusive one before you could drop the old index. If someone else > is waiting to get a conflicting lock, boom ... > I think what I'm confused about is how these non-transactional commands work (like VACUUM, etc). Are they still transactions, and just can't be run in a block? My original thinking was that the shared lock could be unlocked before the exclusive lock is taken to switch the relfilenodes and to drop the index. However, if it is a real transaction, clearly you can't unlock in the middle. Is it safe to manually run the sequence I previously suggested? If so it seems like there could be a command to do it properly. I tried it and it appeared to work. Regards, Jeff Davis
