Horton

Re: per backend I/O statistics

Michael Paquier <michael@paquier.xyz>

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From: Michael Paquier <michael@paquier.xyz>
To: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Cc: Nazir Bilal Yavuz <byavuz81@gmail.com>, Alvaro Herrera <alvherre@alvh.no-ip.org>, Kyotaro Horiguchi <horikyota.ntt@gmail.com>, pgsql-hackers@lists.postgresql.org
Date: 2024-12-19T04:21:54Z
Lists: pgsql-hackers 
On Wed, Dec 18, 2024 at 08:11:55AM +0000, Bertrand Drouvot wrote:
> I think I prefer pg_stat_io_build_tuples() and used that name in v11
> attached.

I'll rely to your naming sense than mine, then :D

> I think that this comment is now confusing since the extra loop would be
> done in pg_stat_io_build_tuples() and not where the comment is written. One
> option could have been to move the assert and the comment in pg_stat_io_build_tuples()
> but I think it's better to have the assert before the pgstat_tracks_io_bktype()
> call in pg_stat_get_io(), so modified the comment a bit instead.
> 
> 0002 is the per-backend stats I/O with yours tweaks.

While doing more tests with backends exiting concurrently with their
stats scanned, I have detected one path in pg_stat_get_backend_io()
after calling pgstat_get_beentry_by_proc_number() where we should also
check that it does not return NULL, or we would crash on a pointer
dereference when reading the backend type.

Fixed that, bumped the two version counters, and done.
--
Michael

Commits

  1. Rework handling of pending data for backend statistics

  2. Rename some pgstats callbacks related to flush of entries

  3. Relax regression test for fsync check of backend-level stats

  4. Add backend-level statistics to pgstats

  5. Extract logic filling pg_stat_get_io()'s tuplestore into its own routine

  6. Tweak some comments related to variable-numbered stats in pgstat.c