Re: Intermittent BRIN failures on hyrax and lousyjack

On 2020-Jul-09, Tom Lane wrote:

> Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> writes:
> > On 2020-Jun-30, Tom Lane wrote:
> >> SELECT brin_desummarize_range('brinidx', 0);
> >> +WARNING: leftover placeholder tuple detected in BRIN index "brinidx", deleting
>
> >> So (1) the comment needs to be adjusted to mention that vacuum
> >> cancellation is enough to create the situation, and (2) probably the
> >> message needs to be downgraded quite a lot, DEBUG2 or even less.
> >> Or maybe we could just delete the quoted stanza altogether.
>
> > Yeah, maybe deleting the whole thing is a decent answer. When I wrote
> > that, I was thinking that it was a very unlikely event, but evidently
> > that's not true.
>
> trilobite (also a CCA animal) just reported one of these, too:
>
> https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=trilobite&dt=2020-07-09%2008%3A03%3A08
>
> Were you going to fix this, or did you expect me to?

I have a moment now, let me have a go at it. I agree with deleting the
message. I think I'll keep the comment, slightly reworded:

/*
* Placeholder tuples only appear during unfinished summarization, and we
* hold SUE lock, so this function cannot run concurrently with
* that. Any placeholder tuples that exist must be leftovers from a
* crashed or aborted summarization; remove them silently.
*/

--
Álvaro Herrera https://www.2ndQuadrant.com/
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