Re: Track the amount of time waiting due to cost_delay

On Mon, Jun 10, 2024 at 02:20:16PM -0500, Nathan Bossart wrote:
> On Mon, Jun 10, 2024 at 05:48:22PM +0000, Bertrand Drouvot wrote:
> > On Mon, Jun 10, 2024 at 10:36:42AM -0500, Nathan Bossart wrote:
> >> I wonder if we should also
> >> surface the effective cost limit for each autovacuum worker.
> >
> > I'm not sure about it as I think that it could be misleading: one could query
> > pg_stat_progress_vacuum and conclude that the time_delayed he is seeing is
> > due to _this_ cost_limit. But that's not necessary true as the cost_limit could
> > have changed multiple times since the vacuum started. So, unless there is
> > frequent sampling on pg_stat_progress_vacuum, displaying the time_delayed and
> > the cost_limit could be misleadind IMHO.
>
> Well, that's true for the delay, too, right (at least as of commit
> 7d71d3d)?

Yeah right, but the patch exposes the total amount of time the vacuum has
been delayed (not the cost_delay per say) which does not sound misleading to me.

Regards,

--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com