Horton

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

Pavel Luzanov <p.luzanov@postgrespro.ru>

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From: Pavel Luzanov <p.luzanov@postgrespro.ru>
To: Melanie Plageman <melanieplageman@gmail.com>
Cc: Justin Pryzby <pryzby@telsasoft.com>, Andres Freund <andres@anarazel.de>, Kyotaro Horiguchi <horikyota.ntt@gmail.com>, tgl@sss.pgh.pa.us, vignesh21@gmail.com, lukas@fittl.com, alvherre@alvh.no-ip.org, magnus@hagander.net, pgsql-hackers@postgresql.org, thomas.munro@gmail.com, m.sakrejda@gmail.com
Date: 2023-04-04T20:35:13Z
Lists: pgsql-hackers 
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

Commits

  1. Stabilize pg_stat_io writes test

  2. Fix flakey pg_stat_io test

  3. Suppress more compiler warnings in new pgstats code.

  4. Suppress compiler warnings in new pgstats code.

  5. Add tests for pg_stat_io

  6. Create regress_tblspc in test_setup

  7. Add pg_stat_io view, providing more detailed IO statistics

  8. pgstat: Track more detailed relation IO statistics

  9. pgstat: Infrastructure for more detailed IO statistics

  10. doc: Fix some issues in logical replication section

  11. Manual cleanup and pgindent of pgstat and bufmgr related code

  12. Have the planner consider Incremental Sort for DISTINCT

  13. Use actual backend IDs in pg_stat_get_backend_idset() and friends.

  14. Remove redundant call to pgstat_report_wal()

  15. Add BackendType for standalone backends

  16. Initialize backend status reporting during bootstrap.