Re: vacuum_cost_page_miss default value and modern hardware

On Thu, Jan 14, 2021 at 1:24 AM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
>
> On Wed, Jan 6, 2021 at 7:43 PM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> > More concretely, we could perhaps lower vacuum_cost_page_miss to 5. It
> > has had the value as 10 as its default since 2004 (just like
> > vacuum_cost_page_dirty, whose default has also not been changed since
> > the start). These defaults were decided in a time when nbtree VACUUM
> > could do lots of random I/O, there was no visibility map, etc. So this
> > refresh is not just about hardware.
>
> Attached patch lowers vacuum_cost_page_miss to 3. I think that this
> change in the default is both likely to be helpful in medium to large
> installations, and unlikely to cause harm in small installations. If
> I/O for reads made by VACUUM is naturally very slow (even in the
> common case where it's entirely sequential), then that will naturally
> provide additional throttling.

+1 for this in principle.

Do you have any actual metrics between specifically choosing the value
3? Or is that off a gut feeling?

--
Magnus Hagander
Me: https://www.hagander.net/
Work: https://www.redpill-linpro.com/