| From: | Nico Williams <nico(at)cryptonector(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Konstantin Knizhnik <knizhnik(at)garret(dot)ru>, pgsql-hackers(at)lists(dot)postgresql(dot)org |
| Subject: | Re: Non-reproducible AIO failure |
| Date: | 2025-06-07 04:28:12 |
| Message-ID: | aEO/3F25PiFuoru6@ubby |
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| Thread: | |
| Lists: | pgsql-hackers |
On Fri, Jun 06, 2025 at 03:37:45PM -0400, Andres Freund wrote:
> On 2025-06-06 15:21:13 -0400, Tom Lane wrote:
> > So it's our code that is busted. No doubt, what is happening is
> > that process A is fetching two fields, modifying one of them,
> > and storing the word back (with the observed value of the other
> > field) concurrently with some other process trying to update
> > the other field. So the other process's update is lost.
>
> There shouldn't be any concurrent accesses here, so I don't really see
> how the above would explain the problem (the IO can only ever be
> modified by one backend, initially the "owning backend", then, when
> submitted, by the IO worker, and then again by the backend).
No concurrent accesses, not from threads anyways, but not even from
kernel subsystems nor from signal handlers?
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