Horton

Re: Pluggable cumulative statistics

Michael Paquier <michael@paquier.xyz>

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From: Michael Paquier <michael@paquier.xyz>
To: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Cc: Postgres hackers <pgsql-hackers@lists.postgresql.org>
Date: 2024-07-08T06:49:34Z
Lists: pgsql-hackers 
On Mon, Jul 08, 2024 at 06:39:56AM +0000, Bertrand Drouvot wrote:
> +       for (int kind = PGSTAT_KIND_FIRST_VALID; kind <= PGSTAT_KIND_LAST; kind++)
> +       {
> +               char       *ptr;
> +               const PgStat_KindInfo *info = pgstat_get_kind_info(kind);
> 
> I wonder if we could avoid going through stats that are not fixed ones. What about
> doing something like?
> Same would apply for the read part added in 9004abf6206e.

This becomes more relevant when the custom stats are added, as this
performs a scan across the full range of IDs supported.  So this
choice is here for consistency, and to ease the pluggability.

> 2 ===
> 
> +               pgstat_build_snapshot_fixed(kind);
> +               ptr = ((char *) &pgStatLocal.snapshot) + info->snapshot_ctl_off;
> +               write_chunk(fpout, ptr, info->shared_data_len);
> 
> I think that using "shared_data_len" is confusing here (was not the case in the
> context of 9004abf6206e). I mean it is perfectly correct but the wording "shared"
> looks weird to me when being used here. What it really is, is the size of the
> stats. What about renaming shared_data_len with stats_data_len?

It is the stats data associated to a shared entry.  I think that's OK,
but perhaps I'm just used to it as I've been staring at this area for
days.
--
Michael

Commits

  1. injection_points: Add some fixed-numbered statistics

  2. injection_points: Add some cumulative stats for injection points

  3. Add helper routines to retrieve data for custom fixed-numbered pgstats

  4. Introduce pluggable APIs for Cumulative Statistics

  5. Switch PgStat_Kind from an enum to a uint32 type

  6. Improve comment of pgstat_read_statsfile()

  7. Add a new 'F' entry type for fixed-numbered stats in pgstats file

  8. Add PgStat_KindInfo.init_shmem_cb

  9. Use pgstat_kind_infos to write fixed shared statistics

  10. Replace hardcoded identifiers of pgstats file by #defines