Horton

Re: Assertion failure with LEFT JOINs among >500 relations

David Rowley <dgrowleyml@gmail.com>

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From: David Rowley <dgrowleyml@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Onder Kalaci <onderk@microsoft.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2020-10-09T04:32:35Z
Lists: pgsql-hackers 
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

Commits

  1. Relax some asserts in merge join costing code

  2. Prevent overly large and NaN row estimates in relations

  3. Avoid a couple of zero-divide scenarios in the planner.

  4. Guard against incoming rowcount estimate of NaN in cost_mergejoin().

  5. When a relation has been proven empty by constraint exclusion, propagate that