| From: | David Rowley <dgrowleyml(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Onder Kalaci <onderk(at)microsoft(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Assertion failure with LEFT JOINs among >500 relations |
| Date: | 2020-10-09 04:32:35 |
| Message-ID: | CAApHDvoOyLH5HvGmzGpXACRBEXSkt7-1p0uAcFAy7ZKt_-bYWg@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Fri, 9 Oct 2020 at 15:06, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)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
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