Re: "could not find pathkey item to sort" for TPC-DS queries 94-96

On Sun, Apr 18, 2021 at 1:21 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> I wrote:
> > I think it's time for some refactoring of this code so that we can
> > actually share the logic.  Accordingly, I propose the attached.
>
> After sleeping on it, here's an improved version that gets rid of
> an unnecessary assumption about ECs usually not containing both
> parallel-safe and parallel-unsafe members.  I'd tried to do this
> yesterday but didn't like the amount of side-effects on createplan.c
> (caused by the direct call sites not being passed the "root" pointer).
> However, we can avoid refactoring createplan.c APIs by saying that it's
> okay to pass root = NULL to find_computable_ec_member if you're not
> asking it to check parallel safety.  And there's not really a need to
> put a parallel-safety check into find_ec_member_matching_expr at all;
> that task can be left with the one caller that cares.

I like the refactoring here.

Two things I wonder:
1. Should we add tests for the relabel code path?
2. It'd be nice not to have the IS_SRF_CALL duplicated, but that might
add enough complexity that it's not worth it.

Thanks,
James Coleman