Robert Haas <robertmhaas@gmail.com> writes:
> On Tue, Mar 23, 2010 at 8:30 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Not unless you'd like to solve the issues with triggers on system
>> catalogs first ...
> Urp. Not really, though I don't know what they are exactly. I didn't
> think exclusion constraints depended on triggers. UNIQUE constraints
> work on system catalogs, right?
UNIQUE constraints depend on internal support in the index access method
(see today's thread with Gokulakannan Somasundaram for some details of
how btree does it). Exclusion constraints have a totally different
implementation --- they don't require index AM support, but they do use
triggers.
Now having said that, my recollection is that the worst issues
surrounding triggers on catalogs had to do with BEFORE triggers.
Exclusion constraint triggers would be AFTER triggers, so maybe it could
be made to work. It'd still be significant work though, for not a lot
of value as far as this particular issue goes.
regards, tom lane