Re: backend crash

On Mon, Apr 13, 2020 at 11:01:01AM -0400, Tom Lane wrote:
>Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> writes:
>> On Mon, Apr 13, 2020 at 09:25:35AM +0200, Kamil Jońca wrote:
>>> I have problem with (pseudo) random backend crashes.
>>> They seems to happen at one query, but not every time.
>
>> I've tried to reproduce this, but unfortunately it does not fail for me.
>> Chances are this depends on data. Can you prepare a small data sample
>> that would trigger the issue?
>
>This is evidently a parallel-query worker, so it's unlikely you'd ever
>get anywhere near this crash with a "small" data sample; for starters
>there'd have to be enough data to prompt use of a parallel plan.
>
>I doubt that the crash is very data-specific though. Maybe just fill
>the table with a lot of dummy data?
>

I did that, of course, and the plan looks like this:

QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------------------------
Finalize Aggregate (cost=315448.35..315448.36 rows=1 width=8) (actual time=18685.398..18685.400 rows=1 loops=1)
-> Gather (cost=315447.52..315448.33 rows=8 width=8) (actual time=18683.862..18687.698 rows=8 loops=1)
Workers Planned: 8
Workers Launched: 7
-> Partial Aggregate (cost=314447.52..314447.53 rows=1 width=8) (actual time=18669.777..18669.781 rows=1 loops=8)
-> Result (cost=0.00..299447.50 rows=12500000 width=40) (actual time=0.160..17844.793 rows=250000 loops=8)
-> ProjectSet (cost=0.00..80697.50 rows=12500000 width=32) (actual time=0.145..14854.132 rows=250000 loops=8)
-> Parallel Seq Scan on log (cost=0.00..16947.50 rows=125000 width=81) (actual time=0.026..343.471 rows=125000 loops=8)
Filter: (account = 'onet'::text)
Planning Time: 0.223 ms
Execution Time: 18687.862 ms
(11 rows)

but still no crashes. I've even built from the exact 12.2 commit to make
sure the bug was not accidentally fixed by some commit since then.

regards

--
Tomas Vondra http://www.2ndQuadrant.com
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