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From: Pavel Luzanov <p.luzanov@postgrespro.ru>
To: Melanie Plageman <melanieplageman@gmail.com>
Cc: Justin Pryzby <pryzby@telsasoft.com>
Cc: Andres Freund <andres@anarazel.de>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Cc: tgl@sss.pgh.pa.us
Cc: vignesh21@gmail.com
Cc: lukas@fittl.com
Cc: alvherre@alvh.no-ip.org
Cc: magnus@hagander.net
Cc: pgsql-hackers@postgresql.org
Cc: thomas.munro@gmail.com
Cc: m.sakrejda@gmail.com
Subject: Re: pg_stat_bgwriter.buffers_backend is pretty meaningless (and more?)
Date: Tue, 4 Apr 2023 23:35:13 +0300
Message-ID: <d9913624-9cb1-d238-21f7-266f0a1eef82@postgrespro.ru> (raw)
In-Reply-To: <CAAKRu_bk1LTUezVwTO+NLcXp9TTmLtdUnmFHskzniNo6ThqxvQ@mail.gmail.com>
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On 03.04.2023 23:50, Melanie Plageman wrote:
> Attached is a tiny patch to add standalone backend type to
> pg_stat_activity documentation (referenced by pg_stat_io).
>
> I mentioned both the bootstrap process and single user mode process in
> the docs, though I can't imagine that the bootstrap process is relevant
> for pg_stat_activity.

After a little thought... I'm not sure about the term 'bootstrap 
process'. I can't find this term in the documentation.
Do I understand correctly that this is a postmaster? If so, then the 
postmaster process is not shown in pg_stat_activity.

Perhaps it may be worth adding a description of the standalone backend 
to pg_stat_io, not to pg_stat_activity.
Something like: backend_type is all types from pg_stat_activity plus 
'standalone backend',
which is used for the postmaster process and in a single user mode.

> I also noticed that the pg_stat_activity docs call background workers
> "parallel workers" (though it also mentions that extensions could have
> other background workers registered), but this seems a bit weird because
> pg_stat_activity uses GetBackendTypeDesc() and this prints "background
> worker" for type B_BG_WORKER. Background workers doing parallelism tasks
> is what users will most often see in pg_stat_activity, but I feel like
> it is confusing to have it documented as something different than what
> would appear in the view. Unless I am misunderstanding something...

'parallel worker' appears in the pg_stat_activity for parallel queries. 
I think it's right here.

-- 
Pavel Luzanov
Postgres Professional: https://postgrespro.com






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  Cc: p.luzanov@postgrespro.ru, melanieplageman@gmail.com, pryzby@telsasoft.com, andres@anarazel.de, horikyota.ntt@gmail.com, tgl@sss.pgh.pa.us, vignesh21@gmail.com, lukas@fittl.com, alvherre@alvh.no-ip.org, magnus@hagander.net, thomas.munro@gmail.com, m.sakrejda@gmail.com
  Subject: Re: pg_stat_bgwriter.buffers_backend is pretty meaningless (and more?)
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