| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Nathan Bossart <nathandbossart(at)gmail(dot)com>, Melanie Plageman <melanieplageman(at)gmail(dot)com>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Michael Paquier <michael(at)paquier(dot)xyz>, Fujii Masao <masao(dot)fujii(at)oss(dot)nttdata(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: race condition when writing pg_control |
| Date: | 2024-05-16 18:58:05 |
| Message-ID: | 20240516185805.hnbt2tr23q7xbx3m@awork3.anarazel.de |
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| Lists: | pgsql-hackers |
Hi,
On 2024-05-16 14:50:50 -0400, Tom Lane wrote:
> Nathan Bossart <nathandbossart(at)gmail(dot)com> writes:
> > I suspect it will be difficult to investigate this one too much further
> > unless we can track down a copy of the control file with the bad checksum.
> > Other than searching for any new code that isn't doing the appropriate
> > locking, maybe we could search the buildfarm for any other occurrences. I
> > also seem some threads concerning whether the way we are reading/writing
> > the control file is atomic.
>
> The intention was certainly always that it be atomic. If it isn't
> we have got *big* trouble.
We unfortunately do *know* that on several systems e.g. basebackup can read a
partially written control file, while the control file is being
updated. Thomas addressed this partially for frontend code, but not yet for
backend code. See
https://postgr.es/m/CA%2BhUKGLhLGCV67NuTiE%3Detdcw5ChMkYgpgFsa9PtrXm-984FYA%40mail.gmail.com
Greetings,
Andres Freund
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