Horton

Re: Track the amount of time waiting due to cost_delay

Bertrand Drouvot <bertranddrouvot.pg@gmail.com>

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From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Nathan Bossart <nathandbossart@gmail.com>, "Imseih (AWS), Sami" <simseih@amazon.com>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>
Date: 2024-06-12T11:27:23Z
Lists: pgsql-hackers

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  1. Add delay time to VACUUM/ANALYZE (VERBOSE) and autovacuum logs.

  2. Add cost-based vacuum delay time to progress views.

  3. Add is_analyze parameter to vacuum_delay_point().

  4. Refresh cost-based delay params more frequently in autovacuum

Hi,

On Tue, Jun 11, 2024 at 02:48:30PM -0400, Robert Haas wrote:
> On Tue, Jun 11, 2024 at 2:47 PM Nathan Bossart <nathandbossart@gmail.com> wrote:
> > I'm struggling to think of a scenario in which the number of waits would be
> > useful, assuming you already know the amount of time spent waiting.

If we provide the actual time spent waiting, providing the number of waits would
allow to see if there is a diff between the actual time and the intended time
(i.e: number of waits * cost_delay, should the cost_delay be the same during
the vacuum duration). That should trigger some thoughts if the diff is large
enough.

I think that what we are doing here is to somehow add instrumentation around the
"WAIT_EVENT_VACUUM_DELAY" wait event. If we were to add instrumentation for wait
events (generaly speaking) we'd probably also expose the number of waits per
wait event (in addition to the time waited).

Regards,

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