Re: MultiXactId wraparound and last aggressive vacuum time

On Mon, 5 Apr 2021 17:28:06 -0400
Michael Schanne <michael.schanne@gmail.com> wrote:

> After a closer reading of the documentation, it appears the database should
> stop accepting new transactions before a wraparound would ever occur.  If
> so, then the only possible explanations for this multixactid wraparound
> error would be data corruption, or a bug in postgresql.  The exact version
> I'm using is 9.6.10, which is quite a few versions behind the latest
> (9.6.21), but I skimmed through the release notes of the later versions and
> did not see any bugfixes in this area.  That would leave data corruption as
> the only explanation.  Is my reasoning correct here?

I didn't checked the changelog, and you should definitely run 9.6.21, but I
believe your reasoning is correct anyway. A bug might be possible, but I would
bet a coin on the corruption.

You might want to compare this number with the value reported by: 

  pg_controldata $PGDATA|grep NextMultiXactId

Backup your cluster, then, try to isolate the table(s) and block(s) where the
corruption occurs and check at them using eg. pageinspect.

> I'm willing to upgrade but I would need to justify it somehow, so if I am
> missing something please let me know.

you can justify the upgrade using this load of reasons:
https://why-upgrade.depesz.com/show?from=9.6.10&to=9.6.21

Regards,