| From: | Bertrand Drouvot <bertranddrouvot(dot)pg(at)gmail(dot)com> |
|---|---|
| To: | Jim Nasby <jnasby(at)upgrade(dot)com> |
| Cc: | Alena Rybakina <a(dot)rybakina(at)postgrespro(dot)ru>, Ilia Evdokimov <ilya(dot)evdokimov(at)tantorlabs(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, Alexander Korotkov <aekorotkov(at)gmail(dot)com>, Kirill Reshke <reshkekirill(at)gmail(dot)com>, Andrei Zubkov <zubkov(at)moonset(dot)ru>, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Melanie Plageman <melanieplageman(at)gmail(dot)com>, jian he <jian(dot)universality(at)gmail(dot)com>, a(dot)lepikhov(at)postgrespro(dot)ru, Sami Imseih <samimseih(at)gmail(dot)com> |
| Subject: | Re: Vacuum statistics |
| Date: | 2025-03-13 06:42:57 |
| Message-ID: | Z9J+cRHwpBt4cQv3@ip-10-97-1-34.eu-west-3.compute.internal |
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| Lists: | pgsql-hackers |
Hi,
On Wed, Mar 12, 2025 at 05:15:53PM -0500, Jim Nasby wrote:
> The usecase I can see here is that we don't want autovac creating so much
> WAL traffic that it starts forcing other backends to have to write WAL out.
> But tracking how many times autovac writes WAL buffers won't help with that
Right, because the one that increments the wal_buffers_full metric could "just"
be a victim (i.e the one that happens to trigger the WAL buffers disk flush,
even though other backends contributed most of the buffer usage).
> (though we also don't want any WAL buffers written by autovac to be counted
> in the system-wide wal_buffers_full:
why? Or do you mean that it would be good to have 2 kinds of metrics: one
generated by "maintenance" activity and one by "regular" backends?
> What would be helpful would be a way to determine if autovac was causing
> enough traffic to force other backends to write WAL. Offhand I'm not sure
> how practical that actually is though.
a051e71e28a could help to see how much WAL has by written by the autovac workers.
> BTW, there's also an argument to be made that autovac should throttle
> itself if we're close to running out of available WAL buffers...
hmm, yeah I think that's an interesting idea OTOH that would mean to "delegate"
the WAL buffers flush to another backend.
Regards,
--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com
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