Re: Assertion failure with LEFT JOINs among >500 relations

On Mon, 19 Oct 2020 at 12:25, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> David Rowley <dgrowleyml@gmail.com> writes:
> > On Mon, 19 Oct 2020 at 12:10, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> >> TBH, I see no need to do anything in the back branches.  This is not
> >> an issue for production usage.
>
> > I understand the Assert failure is pretty harmless, so non-assert
> > builds shouldn't suffer too greatly.  I just assumed that any large
> > stakeholders invested in upgrading to a newer version of PostgreSQL
> > may like to run various tests with their application against an assert
> > enabled version of PostgreSQL perhaps to gain some confidence in the
> > upgrade. A failing assert is unlikely to inspire additional
> > confidence.
>
> If any existing outside regression tests hit such corner cases, then
> (a) we'd have heard about it, and (b) likely they'd fail in the older
> branch as well.  So I don't buy the argument that this will dissuade
> somebody from upgrading.

hmm, well it was reported to us. Perhaps swapping the word "upgrading"
for "migrating".

It would be good to hear Onder's case to see if he has a good argument
for having a vested interest in pg13 not failing this way with assets
enabled.

> I do, on the other hand, buy the idea that if anyone is indeed working
> in this realm, they might be annoyed by a behavior change in a stable
> branch.  So it cuts both ways.  On balance I don't think we should
> touch this in the back branches.

I guess we could resolve that concern by just changing the failing
assert to become: Assert(outer_skip_rows <= outer_rows ||
isinf(outer_rows));

It's pretty grotty but should address that concern.

David