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>, pgsql-hackers@lists.postgresql.org, Nazir Bilal Yavuz <byavuz81@gmail.com>
Date: 2025-02-27T03:02:51Z
Lists: pgsql-hackers 
On Wed, Feb 26, 2025 at 10:59:11AM +0000, Bertrand Drouvot wrote:
> Yup. That's what we've done in pg_stat_io_build_tuples() too (ff7c40d7fd6).
> Without this we'd get "2000-01-01 00:00:00+00" in the stats_reset field of
> pg_stat_get_backend_wal() and pg_stat_get_backend_io().

Right, forgot about this part.

> That was not needed for pg_stat_io and pg_stat_wal because the stats_reset field
> was already non null after initdb.

0001 was OK, so done.

In 0002, couldn't it be better to have the pg_stat_get_backend_stats()
static in pgstatfuncs.c?  In 0003, pg_stat_get_backend_wal() is also
in pgstatfuncs.c, meaning that all the callers of
pg_stat_get_backend_stats() would be in this file.

-typedef struct PgStat_Backend
-{
-	TimestampTz stat_reset_timestamp;
-	PgStat_BktypeIO io_stats;
-} PgStat_Backend;
-
 /* ---------
  * PgStat_BackendPending	Non-flushed backend stats.
  * ---------

In 0003, let's keep PgStat_BackendPending grouped with PgStat_Backend,
so it sounds better to move both of them after the WAL stats
structures.
--
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