Re: BUG #16807: Assert failed in postgres_fdw/estimate_path_cost_size with an empty foreign table

On Thu, Jan 14, 2021 at 1:30 PM Kyotaro Horiguchi
<horikyota(dot)ntt(at)gmail(dot)com> wrote:
> At Thu, 14 Jan 2021 11:56:08 +0900, Etsuro Fujita <etsuro(dot)fujita(at)gmail(dot)com> wrote in
> > If foreignrel->tuples is set to zero, the retrieved_rows estimate will
> > also be set to zero, so the assertion pointed out upthread is not
> > correct. I think I mistakenly assumed that foreignrel->tuples would
> > have been forced to be at least one row, like foreignrel->rows, before
> > we get to estimate_path_cost_size(), which is not correct.
> >
> > To fix, I think it would be better to adjust the assertion accordingly
> > than removing it, since it was added to make sure that the
> > retrieved_rows estimate is set to a sensible value. Attached is a
> > patch for that. I added a simpler test case as well.
>
> FWIW I drew the same conclusion.

Ok, thanks for reviewing!

I tweaked a regression test comment a little bit and added the commit
message. Attached is an updated patch. I’ll commit the patch.

Best regards,
Etsuro Fujita