Re: Assertion failure with LEFT JOINs among >500 relations

On Fri, 9 Oct 2020 at 15:06, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> I notice there are some other ad-hoc isnan() checks scattered
> about costsize.c, too.  Maybe we should indeed consider fixing
> clamp_row_estimate to get rid of inf (and nan too, I suppose)
> so that we'd not need those.  I don't recall the exact cases
> that made us introduce those checks, but they were for cases
> a lot more easily reachable than this one, I believe.

Is there actually a case where nrows could be NaN?  If not, then it
seems like a wasted check.  Wouldn't it take one of the input
relations or the input rels to have an Inf row estimate (which won't
happen after changing clamp_row_estimate()), or the selectivity
estimate being NaN.

David