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Re: Check constraints on partition parents only?

From: Andrew Dunstan <andrew(at)dunslane(dot)net>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Nikhil Sontakke <nikhil(dot)sontakke(at)enterprisedb(dot)com>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Jerry Sievers <gsievers19(at)comcast(dot)net>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Check constraints on partition parents only?
Date: 2011-07-26 13:33:51
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers

On 07/26/2011 09:08 AM, Robert Haas wrote:
> On Tue, Jul 26, 2011 at 4:12 AM, Nikhil Sontakke
> <nikhil(dot)sontakke(at)enterprisedb(dot)com>  wrote:
>>> Yeah.  I think it's good that there's a barrier to blindly dropping a
>>> constraint that may be important to have on children, but there should
>>> be a way to override that.
>> Hmmm, but then it does open up the possibility of naive users shooting
>> themselves in the foot. It can be easy to conjure up a
>> parent-only-constraint that does not gel too well with its children. And
>> that's precisely why this feature was added in the first place..
> Yeah, but I think we need to take that chance.  At the very least, we
> need to support the equivalent of a non-inherited CHECK (false) on
> parent tables.

Indeed. I usually enforce that with a trigger that raises an exception, 
but of course that doesn't help at all with constraint exclusion, and I 
saw a result just a few weeks ago (I forget the exact details) where it 
appeared that the plan chosen was significantly worse because the parent 
table wasn't excluded, so there's a  non-trivial downside from having 
this restriction.



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