Re: shared-memory based stats collector - v70

On Wed, Apr 6, 2022 at 4:12 PM Andres Freund <andres(at)anarazel(dot)de> wrote:

>
> On 2022-04-06 15:32:39 -0700, David G. Johnston wrote:
> > On Wednesday, April 6, 2022, Andres Freund <andres(at)anarazel(dot)de> wrote:
> >
> >
> > I like having the SQL function paired with a matching implementation in
> > this scheme.
>
> It would have gotten things closer than it was before imo. We can't just
> rename the SQL functions, they're obviously exposed API.
>

Right, I meant the naming scheme proposed was acceptable. Not that I
wanted to change the SQL functions too.

I've hacked up the above, but after doing so I think I found a cleaner
>
approach:
>
> I've introduced:
>
> pgstat_reset_of_kind(PgStat_Kind kind) which works for both fixed and
> variable
> numbered stats. That allows to remove pgstat_reset_subscription_counters(),
> pgstat_reset_replslot_counters(), pgstat_reset_shared_counters().
>
> pgstat_reset(PgStat_Kind kind, Oid dboid, Oid objoid), which removes the
> need
> for pgstat_reset_subscription_counter(),
> pgstat_reset_single_counter().

> pgstat_reset_replslot() is still needed, to do
> the name -> index lookup.
>
> That imo makes a lot more sense than requiring each variable-amount kind to
> have wrapper functions.
>
>
I can see benefits of both, or even possibly combining them. Absent being
able to point to some other part of the system and saying "it is done this
way there, let's do the same here" I think the details will inform the
decision. The fact there is just the one outlier here suggests that this
is indeed the better option.

> What does "private" mean for you? They're exposed via pgstat.h not
> pgstat_internal.h. But not to SQL.
>
>
I was thinking specifically of the freedom to rename and not break
extensions. Namely, are these truly implementation details or something
that, while unlikely to be used by extensions, still constitute an exposed
API? It was mainly a passing thought, I'm not looking for a crash-course
in how all that works right now.

David J.