Re: Track the amount of time waiting due to cost_delay

On Mon, Dec 09, 2024 at 04:41:03PM +0000, Bertrand Drouvot wrote:
> + <structfield>time_delayed</structfield> <type>bigint</type>

I think it's also worth considering names like total_delay and
cumulative_delay.

> + Total amount of time spent in milliseconds waiting during <xref linkend="guc-vacuum-cost-delay"/>
> + or <xref linkend="guc-autovacuum-vacuum-cost-delay"/>. In case of parallel
> + vacuum the reported time is across all the workers and the leader. The
> + workers update the column no more frequently than once per second, so it
> + could show slightly old values.

I wonder if it makes sense to provide this value as an interval instead of
the number of milliseconds to make it more human-readable. I might also
suggest some changes to the description:

Total accumulated time spent sleeping due to the cost-based vacuum
delay settings (e.g., vacuum_cost_delay, vacuum_cost_limit). This
includes the time that any associated parallel workers have slept, too.
However, parallel workers report their sleep time no more frequently
than once per second, so the reported value may be slightly stale.

--
nathan