Re: do only critical work during single-user vacuum?

On Tue, Dec 21, 2021 at 12:46 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
>
> Hi,
>
> On 2021-12-20 17:17:26 -0800, Peter Geoghegan wrote:
> > On Thu, Dec 9, 2021 at 8:41 PM Bossart, Nathan <bossartn(at)amazon(dot)com> wrote:
> > > I like the idea of having a built-in function that does the bare
> > > minimum to resolve wraparound emergencies, and I think providing some
> > > sort of simple progress indicator (even if rudimentary) would be very
> > > useful.
> >
> > If John doesn't have time to work on this during the Postgres 15
> > cycle, and if nobody else picks it up, then we should at least do the
> > bare minimum here: force the use of the failsafe in single user mode
> > (regardless of the age of relfrozenxid/relminmxid, which in general
> > might not be that old in tables where VACUUM might need to do a lot of
> > work). Attached quick and dirty patch shows what this would take. If
> > nothing else, it seems natural to define running any VACUUM in single
> > user mode as an emergency.
>
> As I said before I think this is a bad idea. I'm fine with adding a vacuum
> parameter forcing failsafe mode. And perhaps a hint to suggest it in single
> user mode. But forcing it is a bad idea - single user isn't just used for
> emergencies (c.f. initdb, which this patch would regress) and not every
> emergency making single user mode useful is related to wraparound.

+1

BTW a vacuum automatically enters failsafe mode under the situation
where the user has to run a vacuum in the single-user mode, right?

Regards,

--
Masahiko Sawada
EDB: https://www.enterprisedb.com/