Re: Assertion failure with LEFT JOINs among >500 relations

On Fri, 9 Oct 2020 at 12:59, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> If we did want to do something here, I'd consider something like
>
> if (isnan(outer_skip_rows))
> outer_skip_rows = 0;
> if (isnan(inner_skip_rows))
> inner_skip_rows = 0;

Are you worried about the costs above the join that triggers that
coming out as NaN with that fix? It appears that's the case. Cost
comparisons of paths with that are not going to do anything along the
lines of sane.

I guess whether or not that matters depends on if we expect any real
queries to hit this, or if we just want to stop the Assert failure.

... 500 joins. I'm willing to listen to the explanation use case, but
in absence of that explanation, I'd be leaning towards "you're doing
it wrong". If that turns out to be true, then perhaps your proposed
fix is okay.

David