Horton

Re: Pluggable cumulative 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: Postgres hackers <pgsql-hackers@lists.postgresql.org>
Date: 2024-07-08T14:07:58Z
Lists: pgsql-hackers 
Hi,

On Mon, Jul 08, 2024 at 07:22:32AM +0000, Bertrand Drouvot wrote:
> Except the above (which is just a Nit), 0001 LGTM.
> 

Looking at 0002:

It looks pretty straightforward, just one comment:

+                       ptr = ((char *) ctl) + kind_info->shared_ctl_off;
+                       kind_info->init_shmem_cb((void *) ptr);

I don't think we need to cast ptr to void when calling init_shmem_cb(). Looking
at some examples in the code, it does not look like we cast the argument to void
when a function has (void *) as parameter (also there is examples in 0003 where
it's not done, see next comments for 0003).

So I think removing the cast here would be more consistent.

Looking at 0003:

It looks pretty straightforward. Also for example, here:

+               fputc(PGSTAT_FILE_ENTRY_FIXED, fpout);
+               write_chunk_s(fpout, &kind);
                write_chunk(fpout, ptr, info->shared_data_len);

ptr is not casted to void when calling write_chunk() while its second parameter
is a "void *".

+                                       ptr = ((char *) shmem) + info->shared_ctl_off +
+                                               info->shared_data_off;
+
+                                       if (!read_chunk(fpin, ptr,

Same here for read_chunk().

I think that's perfectly fine and that we should do the same in 0002 when
calling init_shmem_cb() for consistency.

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com

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