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: pgsql-hackers@lists.postgresql.org
Date: 2025-01-09T07:05:54Z
Lists: pgsql-hackers

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Hi,

On Thu, Jan 09, 2025 at 01:03:15PM +0900, Michael Paquier wrote:
> On Wed, Jan 08, 2025 at 11:11:59AM +0000, Bertrand Drouvot wrote:
> > Yeah, that's more elegant as it also means that the main callback will not change
> > (should we add even more stats in the future). Done that way in v2 attached.
> 
> I've put my hands on v2-0002 to begin with something.
> 
> +/* flag bits for different types of statistics to flush */
> +#define PGSTAT_FLUSH_IO    (1 << 0) /* Flush I/O statistics */
> +#define PGSTAT_FLUSH_ALL   (PGSTAT_FLUSH_IO)
> 
> These are located and used only in pgstat_backend.c.  It seems to me
> that we'd better declare them in pgstat_internal.h and extend the
> existing pgstat_flush_backend() with an argument so as callers can do
> what they want.
> 
> +	/* Get our own entry_ref if not provided */
> +	if (!entry_ref)
> +		entry_ref = pgstat_get_entry_ref(PGSTAT_KIND_BACKEND, InvalidOid,
> +										 MyProcNumber, false, NULL);
> 
> This relates to the previous remark, actually, where I think that it
> is cleaner to have pgstat_flush_backend() do pgstat_get_entry_ref(),
> same way as HEAD, and just pass down the flags.

I see, so you keep pgstat_flush_backend() calls (with an extra arg) and remove
the new "pgstat_backend_flush_io()" function.

> This comes at the cost of pgstat_flush_backend_entry()
> requiring an extra pgstat_tracks_backend_bktype(), which is not a big
> issue, and the patch gets a bit shorter.

Yeah, all of the above is fine by me.

PFA v3 which is v2 refactoring with your proposed above changes.

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