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

pá 21. 8. 2026 v 19:13 odesílatel Tomas Vondra <tomas(at)vondra(dot)me> napsal:

>
>
> On 8/21/26 17:47, Pavel Stehule wrote:
> > Hi
> >
> > pá 21. 8. 2026 v 12:31 odesílatel Andrey Borodin <x4mmm(at)yandex-team(dot)ru
> > <mailto:x4mmm(at)yandex-team(dot)ru>> napsal:
> >
> > Hi Pavel,
> >
> > On Thu, Aug 20, 2026 at 9:56 PM Pavel Stehule wrote:
> > > We didn't find any way how this issue can be reproduced. We
> manually
> > > executed VACUUM on the database that was restored to the time close
> > > before this issue - and the data was not broken - but now, I am not
> > > sure what was the minor version that we used for this test.
> >
> > I wonder whether the missing TOAST data could be a secondary symptom,
> > rather than evidence that VACUUM removed TOAST belonging to the
> current
> > row version.
> >
> >
> > I have dumped pages
> >
> > https://www.postgresql.org/message-id/attachment/199738/
> > investigation.txt <https://www.postgresql.org/message-id/
> > attachment/199738/investigation.txt>
> >
> > xmin, xmax was same on main table, and toast table. These rows was not
> > updated.
> >
>
> Thanks. Interesting. It's weird the TOAST rows have XID 2779428784 and
> flags {HEAP_HASVARWIDTH,HEAP_XMIN_COMMITTED,HEAP_XMAX_INVALID}, yet the
> VACUUM apparently decided all of them are dead. Judging by:
>
> > rmgr: Heap2 len (rec/tot): 59/ 99, tx: 0, lsn:
> > D6E/8A8A6AD0, prev D6E/8A8A6A68, desc: PRUNE latestRemovedXid 0
> > nredirected 0 ndead 4, blkref #0: rel 1663/4267629/16352341 blk
> 17880358 FPW
>
> I mean, ndead=4 seems to suggest that. But how could that be with
> HEAP_XMIN_COMMITTED?
>
> I wonder if the FPW from the WAL matches what you saw as corrupted, or
> if it's correct (it should, given the ndead=4). But maybe try dumping it
> using pg_waldump - although, 14 doesn't have that :-(.
>
> What happened with the XID 2779428784? Did it commit sometime right
> before the vacuum, or what? Judging by the page LSN, it must have been
> pretty far back.
>
> What does the clog say about this transaction? I think it should be:
> pg_xact/0A5A, page 21, byte offset 175596, bits 0-1, so
>
> $ od -An -tx1 -j 175596 -N 1 $PGDATA/pg_xact/0A5A
>
> Also, what does the RUNNING_XACTS right before/after vacuum say?
>

Unfortunately these backups was overwritten month ago

Regards

Pavel

>
> --
> Tomas Vondra
>
>