> I'm not sure it's needful to go to the NOWAIT extreme on this; the
> conflict conditions would be where you're either doing pg_dump or vacuum
> on the whole database, where it's a big DB; the chances of hitting a
> race condition given the attempt to check locks should be minimal. 
> Trying to avoid locking may be good enough...

I don't see why NOWAIT is an extreme :-) Just do it where you can (i.e.
> 8.x), and then do the lock check... if others still own the lock, bail
out, if not, you're sure you wont lock forever for > 8.x, and have good
chances you won't for < 8.x. Being sure against have good chances worths
doing it, as it won't cost too much.

Cheers,
Csaba.