Re: Berserk Autovacuum (let's save next Mandrill)

On Fri, 2020-03-27 at 10:18 +1300, David Rowley wrote:
> > > I believe there are enough options to disable insert-only vacuuming for
> > > an individual table:
> >
> > > - Set the threshold to 2147483647.  True, that will not work for very
> > >   large tables, but I think that there are few tables that insert that
> > >   many rows before they hit autovacuum_freeze_max_age anyway.
> > >
> > > - Set the scale factor to some astronomical value.
> >
> > Meh. You *are* adding new semantics with these. And they're terrible.
> 
> I've modified this to allow a proper way to disable the entire feature
> by allowing the setting to be set to -1 to disable the feature. I feel
> people are fairly used to using -1 to disable various features (e.g.
> log_autovacuum_min_duration).  I've used the special value of -2 for
> the reloption to have that cascade to using the GUC instead.  The
> autovacuum_vacuum_insert_threshold reloption may be explicitly set to
> -1 to disable autovacuums for inserts for the relation.
> 
> I've also knocked the default threshold down to 1000. I feel this is a
> better value given that the scale factor is now 0.2. There seemed to
> be no need to exclude smaller tables from seeing gains such as
> index-only scans.
> 
> If nobody objects, I plan to push this one shortly.

Thanks for the help!

The new meaning of -2 should be documented, other than that it looks
good to me.

I'll accept the new semantics, but they don't make me happy.  People are
used to -1 meaning "use the GUC value instead".

I still don't see why we need that.  Contrary to Andres' opinion, I don't
think that disabling a parameter by setting it to a value high enough that
it does not take effect is a bad thing.

I won't put up a fight though.

Yours,
Laurenz Albe