On Wed, 11 Mar 2020 at 17:24, Laurenz Albe <laurenz.albe@cybertec.at> wrote:
>
> On Wed, 2020-03-11 at 12:00 +0900, Masahiko Sawada wrote:
> > I might be missing your point but could you elaborate on that in what
> > kind of case you think this lead to unnecessary vacuums?
>
> If you have an insert-only table that has 100000 entries, it will get
> vacuumed roughly every 20000 new entries. The impact is probably too
> little to care, but it will increase the contention for the three
> autovacuum workers available by default.
I guess that depends on your definition of unnecessary. If you want
Index Only Scans, then those settings don't seem unreasonable. If you
want it just to reduce the chances or impact of an anti-wraparound
vacuum then likely it's a bit too often.
I understand this patch was born due to the anti-wraparound case, but
should we really just ignore the Index Only Scan case?