Re: pg_stat_bgwriter.buffers_backend is pretty meaningless (and more?)

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