Horton

Re: per backend WAL statistics

Bertrand Drouvot <bertranddrouvot.pg@gmail.com>

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From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: Xuneng Zhou <xunengzhou@gmail.com>, Michael Paquier <michael@paquier.xyz>, pgsql-hackers@lists.postgresql.org
Date: 2025-03-05T17:26:40Z
Lists: pgsql-hackers

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Hi,

On Wed, Mar 05, 2025 at 09:18:16AM -0500, Andres Freund wrote:
> Hi,
> 
> On 2025-03-05 13:03:07 +0000, Bertrand Drouvot wrote:
> > But yeah, if 0002 in [1] does not go in, then your concern is valid, so adding
> > the extra check in the attached.
> 
> This crashes in cfbot:
> 
> https://cirrus-ci.com/task/5111872610893824
> 

Thanks for the report! I usually always run a make check-world locally and also
launch the CI tests on my github repo before submitting patches. This time,
that was a one line change (as compared to v13), so confident enough I did not
trigger those tests. Murphy's Law I guess ;-)

So yeah, back to the issue, we have to pay more attention for the WAL stats
because pgWalUsage is "incremented" without any check with pgstat_tracks_backend_bktype()
(that's not the case for the IO stats where the counters are incremented taking
into account pgstat_tracks_backend_bktype()).

So for the moment, in the attached I "just" add a pgstat_tracks_backend_bktype()
check in pgstat_backend_have_pending_cb() but I'm not sure I like it that much...

Will think more about it...

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com

Commits

  1. Fix use-after-free in pgstat_fetch_stat_backend_by_pid()

  2. Remove initialization from PendingBackendStats

  3. Add WAL data to backend statistics

  4. Improve check for detection of pending data in backend statistics

  5. Fix some gaps in pg_stat_io with WAL receiver and WAL summarizer

  6. Handle auxiliary processes in SQL functions of backend statistics

  7. Invent pgstat_fetch_stat_backend_by_pid()

  8. Refactor code of pg_stat_get_wal() building result tuple

  9. Adding new PgStat_WalCounters structure in pgstat.h

  10. Remove pgstat_flush_wal()

  11. Refactor some code related to backend statistics

  12. Add backend-level statistics to pgstats