Re: Add pg_stat_kind_info system view

On Mon Jun 1, 2026 at 5:41 AM UTC, Michael Paquier wrote:
> On Thu, May 28, 2026 at 05:11:42PM +0000, Tristan Partin wrote:
>> Can you share how someone might use this additional information?
>>
>> Not sure I understand why we would want to expose the existence of the
>> callbacks to make assertions at the SQL level. I see that in
>> pgstat_register_kind(), we have the following code:
>>
>> We could extend these invariant checks to make sure that the callbacks
>> are only set when fixed_amount is true for instance. I am very much open
>> to having my mind changed.
>
> There is currently no internal mechanism to make sure that the
> built-in stats kinds have a consistent setup in terms of flags and
> callbacks set, so for developers we could immediately complain when
> generating patches that add new stats kinds. For custom stats kinds,
> loaded libraries could have more cross-checks.

I think there is still some confusion on my end about this line of
discussion.

> Perhaps it is not worth bothering at the end, and I'd be fine to keep
> the data published as minimal as you see fit. Still, fixed_amount,
> write_to_file and accessed_across_databases feel like useful
> additions.

The additional columns are now added in v2. Note that I named
write_to_file as written_to_file for the column name. I wonder if
persisted would be a better name for the column and if persisted would
be a better name for PgStat_KindInfo::write_to_file.

> If we keep shared_size, it may make sense to set it to NULL if we
> don't know about it? That's the case of the built-in fixed-sized
> stats kinds. We set the value for custom fixed-sized stats kinds.

I believe that I also captured this correctly in v2.

--
Tristan Partin
PostgreSQL Contributors Team
AWS (https://aws.amazon.com)