Re: DROP SCHEMA xxx CASCADE: ERROR: could not open relation with OID yyy

On Thu, Feb 10, 2011 at 12:03:49AM -0500, Tom Lane wrote:
> strk <strk(at)keybit(dot)net> writes:
> > I've finally completed the debugging phase and have
> > a minimal self-contained testcase showing the problem.
> > It has to do with INITIALLY DEFERRED constraints.
>
> I looked into this and find that the issue is you're trying to drop a
> table that has unfired AFTER TRIGGER events pending. When they finally
> fire, they can't find the table anymore.
>
> I'm inclined to think that we should disallow that; or even more to the
> point, that it'd be a good thing to apply CheckTableNotInUse() when
> about to drop a table. If we disallow such cases for ALTER TABLE, then
> a fortiori we should do so for DROP TABLE.
>
> Aside from disallowing unfired trigger events, CheckTableNotInUse would
> disallow the table being actively relation_open'd by any operation.
> This seems like a real good thing anyway (imagine, eg, DROP TABLE
> executed from a trigger for that table).

+1. We even do it for TRUNCATE, so surely it's proper for DROP.

> It's possible that we could handle the unfired-trigger problem by
> marking the relevant events AFTER_TRIGGER_DONE, but I'm unconvinced that
> it's worth spending effort on.

Seems rare enough not to worry much about, particularly considering the SET
CONSTRAINTS escape hatch.