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

On Fri, 27 Mar 2020 at 07:51, Andres Freund <andres(at)anarazel(dot)de> wrote:
>
> Hi,
>
> On 2020-03-26 10:12:39 +0100, Laurenz Albe wrote:
> > On Wed, 2020-03-25 at 23:19 +0300, Alexander Korotkov wrote:
> > I am reluctant to introduce new semantics like a reloption value of -2
> > to disable a feature in this patch right before feature freeze.
> >
> > 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.

David