Re: [BUG] Remove self joins causes 'variable not found in subplan target lists' error

Richard Guo <guofenglinux(at)gmail(dot)com> writes:
> On Wed, Aug 27, 2025 at 2:26 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> I wonder if the right answer in v18 is to back out a3179ab69.
>> Not fixing that performance regression for another year would
>> be mildly annoying; but AFAIR we've still had only the one
>> complaint, so it seems like it's not hurting many people.
>> And we are getting mighty late in the release calendar to be
>> inventing new stuff in v18.

> Yeah, inventing new stuff in v18 at this point seems risky. I think
> backing out a3179ab69 should be fine for v18.

I had a go at doing that (attached) and the news is not good:
it dumps core in some regression tests added by the SJE patch,
seemingly because there are still references to the removed relid.

Now it might be that I failed to correctly adjust the places
where the revert didn't apply because of SJE-related changes.
But I think what is more likely is that the SJE code is not
bothering to update relids everywhere because it's expecting
a3179ab69's "rebuild" logic to take care of things later.

This leaves us with some pretty unappetizing choices about what
to do in v18:

1. Try to emulate the proposed HEAD fix.

2. Try to fix up the SJE patch so that it calculates relid changes
honestly, or at least no less honestly than what happened before
a3179ab69.

3. Revert SJE as well as a3179ab69 in v18.

I will have a look at #1. If there's somebody who wants to look
at #2, feel free, but it won't be me because I don't understand
the SJE patch well enough. Either way, it's not great to be
doing stuff like this just days before rc1 ...

regards, tom lane