Horton

Re: per backend WAL statistics

Michael Paquier <michael@paquier.xyz>

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From: Michael Paquier <michael@paquier.xyz>
To: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Cc: Andres Freund <andres@anarazel.de>, Xuneng Zhou <xunengzhou@gmail.com>, pgsql-hackers@lists.postgresql.org
Date: 2025-03-08T01:57:38Z
Lists: pgsql-hackers 
On Fri, Mar 07, 2025 at 08:33:04AM +0000, Bertrand Drouvot wrote:
> But when it's time to flush, then pgstat_backend_have_pending_cb() checks
> for zeros in PendingBackendStats *without* any check on the backend type.
> 
> I think the issue is "masked" on HEAD because PendingBackendStats is
> probably automatically initialized with zeros (as being a static variable at
> file scope).

If this weren't true, we would have a lot of problems in more places
than this one.  It does not hurt to add an initialization at the top
of pgstat_backend.c for PendingBackendStats, to document the
intention, while we're on it.

Did both things, and applied the result.
--
Michael

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