Re: autovacuum big table taking hours and sometimes seconds

On Thu, 7 Feb 2019 at 00:17, Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at> wrote:
>
> On Wed, 2019-02-06 at 12:29 +0200, Mariel Cherkassky wrote:
> > Now the question is how to handle or tune it ? Is there any change that I need to increase the cost_limit / cost_delay ?
>
> Maybe configuring autovacuum to run faster will help:
>
> alter table orig_table set (toast.autovacuum_vacuum_cost_limit = 2000);
>
> Or, more extreme:
>
> alter table orig_table set (toast.autovacuum_vacuum_cost_delay = 0);

Going by the block hits/misses/dirtied and the mentioned vacuum times,
it looks like auto-vacuum is set to the standard settings and if so it
spent about 100% of its time sleeping on the job.

It might be a better idea to consider changing the vacuum settings
globally rather than just for one table.

Running a vacuum_cost_limit of 200 is likely something you'd not want
to ever do with modern hardware... well maybe unless you just bought
the latest Raspberry PI, or something. You should be tuning that
value to something that runs your vacuums to a speed you're happy with
but leaves enough IO and CPU for queries running on the database.

If you see that all auto-vacuum workers are busy more often than not,
then they're likely running too slowly and should be set to run more
quickly.

--
David Rowley http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services