Re: Question regarding "Make archiver process an auxiliary process. commit"

On Tue, Dec 6, 2022 at 4:57 PM Sravan Kumar <sravanvcybage(at)gmail(dot)com> wrote:
>
> Thank you for the feedback.
>
> I'll be glad to help with the fix. Here's the patch for review.

Thanks. +1 for fixing this.

I would like to quote recent discussions on reducing the useless
wakeups or increasing the sleep/hibernation times in various processes
to reduce the power savings [1] [2] [3] [4] [5]. With that in context,
does the archiver need to wake up every 60 sec at all when its latch
gets set (PgArchWakeup()) whenever the server switches to a new WAL
file? What happens if we get rid of PGARCH_AUTOWAKE_INTERVAL and rely
on its latch being set? If required, we can spread PgArchWakeup() to
more places, no?

Before even answering the above questions, I think we need to see if
there're any cases where a process can miss SetLatch() calls (I don't
have an answer for that).

Or do we want to stick to what the below comment says?

/*
* There shouldn't be anything for the archiver to do except to wait for a
* signal ... however, the archiver exists to protect our data, so she
* wakes up occasionally to allow herself to be proactive.
*/

[1] https://www.postgresql.org/message-id/CA%2BhUKGJCbcv8AtujLw3kEO2wRB7Ffzo1fmwaGG-tQLuMOjf6qQ%40mail.gmail.com
[2]
commit cd4329d9393f84dce34f0bd2dd936adc8ffaa213
Author: Thomas Munro <tmunro(at)postgresql(dot)org>
Date: Tue Nov 29 11:28:08 2022 +1300

Remove promote_trigger_file.

Previously, an idle startup (recovery) process would wake up every 5
seconds to have a chance to poll for promote_trigger_file, even if that
GUC was not configured. That promotion triggering mechanism was
effectively superseded by pg_ctl promote and pg_promote() a long time
ago. There probably aren't many users left and it's very easy to change
to the modern mechanisms, so we agreed to remove the feature.

This is part of a campaign to reduce wakeups on idle systems.

[3] https://commitfest.postgresql.org/41/4035/
[4] https://commitfest.postgresql.org/41/4020/
[5]
commit 05a7be93558c614ab89c794cb1d301ea9ff33199
Author: Thomas Munro <tmunro(at)postgresql(dot)org>
Date: Tue Nov 8 20:36:36 2022 +1300

Suppress useless wakeups in walreceiver.

Instead of waking up 10 times per second to check for various timeout
conditions, keep track of when we next have periodic work to do.

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