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: 2025-02-17T15:14:59Z
Lists: pgsql-hackers

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Hi,

On Mon, Feb 17, 2025 at 07:59:26AM +0000, Bertrand Drouvot wrote:
> Hi,
> 
> On Mon, Feb 17, 2025 at 04:25:46PM +0900, Michael Paquier wrote:
> > On Mon, Feb 17, 2025 at 06:59:40AM +0000, Bertrand Drouvot wrote:
> > > There is still something that would simplify what is done here: it's the
> > > "the elimination of the write & sync columns for pg_stat_wal" mentioned in [2].
> > 
> > Yeah, still you cannot just remove them because the data tracked in
> > pg_stat_io is not entirely the same, right?
> 
> I think that we can just remove them. They are tracked and incremented at the
> exact same places in issue_xlog_fsync() and XLogWrite(). What differs is the
> "bytes" (as pg_stat_wal.wal_bytes somehow "focus" on the wal records size while
> the pg_stat_io's unit is the wal_block_size) and we keep them in both places.
> Also it looks like we can get rid of PendingWalStats...

PFA the whole picture. 0001 is implementing the fields removal in pg_stat_wal
(and also PendingWalStats). I think that's ok given the backend's type for which
pgstat_tracks_io_bktype() returns false. But now you make me doubt about 0001.
Anyway, it's probably better to move the 0001 discussion to a dedicated thread,
thoughts?

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