Re: toast table corrupted by vacuum - missing chunk number 0 for toast value

ne 23. 8. 2026 v 1:59 odesílatel Peter Geoghegan <pg(at)bowt(dot)ie> napsal:

> On Sat, Aug 22, 2026 at 10:25 AM Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
> wrote:
> > Unfortunately these backups was overwritten month ago
>
> I thought that your complaint might be related to a recently reported
> issue with subxact corruption:
>
> https://postgr.es/m/447185db-3f06-4a38-8518-ecbd42d8b7d5@gmail.com
>
> That case involves a subtransaction that has already subcommitted
> being forced to abort. This reminded me of what Tomas said about it
> being weird that the TOAST table's entry appears to be for a
> committing transaction, yet other evidence suggests that the same XID
> aborted.
>
> I asked Opus 5 to build a test case (based on one from Andrey Borodin
> on that other thread) that produces symptoms consistent with Pavel's
> report. It succeeded in doing so -- see the attached patch adding
> these tests.
>
> These tests fail, demonstrating the same symptoms (you might have to
> comment-out an assertion in clog.c to allow the script to get as far
> as executing the pageinspect steps that show those specific details).
> With Bryan Green's bug fix patch from the other thread applied, the
> tests all pass.
>
> Of course, I'm not claiming that this is incontrovertible proof that
> Pavel's case was an example of this bug causing corruption in the
> field; other bugs have had similar symptoms. For example, the snapshot
> export bug I'm working on [1] can make committed subxacts temporarily
> appear to have aborted, albeit on a standby (that one doesn't fit
> Pavel's reported symptoms but isn't too far off). I still think this
> explanation has a decent chance of being the correct one.
>
> With that said, Pavel should look at this test case and try to find
> any factor that might rule this explanation out. It would be worth
> working out which ERROR actually happened. We simulate an OOM or other
> error using the test's subxact-after-childxids-transfer injection
> point; we don't know what ERROR actually occurred in the field (if we
> assume this really was the bug involved, then some specific error must
> have triggered it).
>
> Question for Pavel: When I run the failing test, I see "WARNING:
> AbortSubTransaction while in COMMIT state" in the test server logs. Do
> any of the logs that you collected show that? If they do, then this
> diagnosis is almost certainly correct.
>

I'll ask the customer - now he it out of office, but I afraid so logs from
this time are already thrown

but I remember so on same server we found a vaccum errors "cannot to freeze
commtted xmax" - I don't know if this is related to this bug, but it was
few weeks after problem with broken TOAST

regards

Pavel

Regards

Pavel

>
> [1]
> https://postgr.es/m/CAH2-WzmHVeYY=pjz9x8DhhxVjXHX0pvoQ-MdiB1Tt6=o2GTiKg@mail.gmail.com
> --
> Peter Geoghegan
>