Horton

Re: per backend WAL statistics

Bertrand Drouvot <bertranddrouvot.pg@gmail.com>

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From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
To: Michael Paquier <michael@paquier.xyz>
Cc: Andres Freund <andres@anarazel.de>, pgsql-hackers@lists.postgresql.org, Nazir Bilal Yavuz <byavuz81@gmail.com>
Date: 2025-03-03T10:47:28Z
Lists: pgsql-hackers

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Hi,

On Mon, Mar 03, 2025 at 09:17:30AM +0000, Bertrand Drouvot wrote:
> hmm, that would work as long as PGSTAT_BACKEND_FLUSH_ALL represents things
> that need to be called from pgstat_report_wal(). But I think that's open
> door for issue should be add a new PGSTAT_BACKEND_FLUSH_XXX where XXX is not
> related to pgstat_report_wal() at all. So, I'm tempted to keep it as it is.

I just realized that pgstat_flush_backend() is not correct in 0001. Indeed
we check:

"
    if (pg_memory_is_all_zeros(&PendingBackendStats,
                               sizeof(struct PgStat_BackendPending)))
        return false;
"

but the WAL stats are not part of PgStat_BackendPending... So we only check
for IO pending stats here. I'm not sure WAL stats could be non empty if IO 
stats are but the attached now also takes care of pending WAL stats here.

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