Re: Analyzing bug 8049

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Thu, Apr 11, 2013 at 1:25 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> The plan I'm considering is to get this written and committed to HEAD
>> in the next week, so that it can go out in 9.3beta1. After the patch
>> has survived a reasonable amount of beta testing, I'd be more comfortable
>> about back-patching into 9.2.

> I'm not very sanguine about the chances that back-patching this won't
> provoke any screams of agony ... but I don't have a better idea,
> either. Letting queries return wrong answers isn't a superior
> solution, for sure.

The only alternative I can see is to make a back-patch that just teaches
get_eclass_for_sort_expr() to compute valid nullable_relids for the sort
expression. That's necessary code in any case, and it would fix the
immediately complained-of bug. The thing that scares me is that it is
now clear that equivclass.c is capable of considering two expressions to
be equivalent when they should not be; that is, I'm afraid there are
variants of the problem that would not be cured by such a limited
back-patch. But maybe I should try to create such an example before
proposing the more invasive approach.

regards, tom lane