Re: PATCH to allow concurrent VACUUMs to not lock each

Neil Conway <neilc(at)samurai(dot)com> writes:
> I'm a little worried about having this set to "true" after a VACUUM is
> executed, and only reset to false when the next transaction is begun: it
> shouldn't affect correctness right now, but it seems like asking for
> trouble. Resetting the flag to "false" after processing a transaction
> would probably be worth doing.

These days I'd be inclined to use a PG_TRY construct to guarantee the
flag is cleared, rather than loading another cleanup operation onto
unrelated code.

The MyProc != NULL tests are a waste of code space. You can't even
acquire an LWLock without MyProc being set, let alone access tables.

The real issue here though is whether anyone can blow a hole in the
xmin assumptions: is there any situation where ignoring a vacuum
transaction breaks things? I haven't had time to think about it
in any detail, but it definitely needs to be thought about.

regards, tom lane