Re: Pluggable cumulative statistics

On Tue, Jul 16, 2024 at 10:27:25AM +0900, Michael Paquier wrote:
> Perhaps we should have a few more inline functions like
> pgstat_get_entry_len() to retrieve the parts of the custom data in the
> snapshot and shmem control structures for fixed-numbered stats.  That
> would limit what extensions need to know about
> pgStatLocal.shmem->custom_data[] and
> pgStatLocal.snapshot.custom_data[], which is easy to use incorrectly.
> They don't need to know about pgStatLocal at all, either.
> 
> Thinking over the weekend on this patch, splitting injection_stats.c
> into two separate files to act as two templates for the variable and
> fixed-numbered cases would be more friendly to developers, as well.

I've been toying a bit with these two ideas, and the result is
actually neater:
- The example for fixed-numbered stats is now in its own new file,
called injection_stats_fixed.c.
- Stats in the dshash are at the same location, injection_stats.c.
- pgstat_internal.h gains two inline routines called
pgstat_get_custom_shmem_data and pgstat_get_custom_snapshot_data that
hide completely the snapshot structure for extensions when it comes to
custom fixed-numbered stats, see the new injection_stats_fixed.c that
uses them.
--
Michael