Re: vacuum_cost_page_miss default value and modern hardware

On Wed, Jan 6, 2021 at 7:43 PM Peter Geoghegan <pg@bowt.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.

I will add this to the final CF for Postgres 14.

Thanks
-- 
Peter Geoghegan