Horton

Re: Pluggable cumulative statistics

Michael Paquier <michael@paquier.xyz>

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From: Michael Paquier <michael@paquier.xyz>
To: Dmitry Dolgov <9erthalion6@gmail.com>
Cc: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>, Postgres hackers <pgsql-hackers@lists.postgresql.org>
Date: 2024-07-28T13:20:45Z
Lists: pgsql-hackers 
On Sat, Jul 27, 2024 at 03:49:42PM +0200, Dmitry Dolgov wrote:
> Agree, looks good. I've tried to quickly sketch out such a fixed
> statistic for some another extension, everything was fine and pretty
> straightforward.

That's my hope.  Thanks a lot for the feedback.

> One question, why don't you use
> pgstat_get_custom_shmem_data & pgstat_get_custom_snapshot_data outside
> of the injection points code? There seems to be a couple of possible
> places in pgstats itself.

Because these two helper routines are only able to fetch the fixed
data area in the snapshot and the control shmem structures for the
custom kinds, not the in-core ones.  We could, but the current code is
OK as well.  My point was just to ease the pluggability effort.

I would like to apply this new infrastructure stuff and move on to the
problems related to the scability of pg_stat_statements.  So, are
there any objections with all that?
--
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