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

On Tue, Dec 21, 2021 at 10:39 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>
> On Wed, Dec 22, 2021 at 6:56 AM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> >
> > This new command/facility should probably not be a new flag to the
> > VACUUM command, as such. Rather, I think that it should either be an
> > SQL-callable function, or a dedicated top-level command (that doesn't
> > accept any tables). The only reason to have this is for scenarios
> > where the user is already in a tough spot with wraparound failure,
> > like that client of yours. Nobody wants to force the failsafe for one
> > specific table. It's not general purpose, at all, and shouldn't claim
> > to be.
>
> Even not in the situation where the database has to run as the
> single-user mode to freeze tuples, I think there would be some use
> cases where users want to run vacuum (in failsafe mode) on tables with
> relfrozenxid/relminmxid greater than their failsafe thresholds before
> falling into that situation. I think it’s common that users are
> somehow monitoring relfrozenxid/relminmxid and want to manually run
> vacuum on them rather than relying on autovacuums. --min-xid-age
> option and --min-mxid-age option of vacuumdb command would be good
> examples. So I think this new command/facility might not necessarily
> need to be specific to single-user mode.

If we want to leave open the possibility to specify these parameters,
a SQL-callable function seems like the way to go. And even if we
don't, a function is fine.

--
John Naylor
EDB: http://www.enterprisedb.com