Re: archive modules

On Thu, Jul 07, 2022 at 11:48:20AM -0400, Tom Lane wrote:
> Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> writes:
>> Well, this does sound unsatisfactory. I suppose one answer would be to
>> load the module in all backends, in case the user wants to look at the
>> value. But that would be wasteful. Maybe we should have a warning
>> about it in the docs -- tell people to LOAD the library if they want to
>> examine the configuration?

Yeah, for something like basic_archive, it should be fine to load it via
shared_preload_libraries or LOAD as well as archive_library, but not all
archive libraries might be written to handle that correctly. And this is
not the most user-friendly.

> The underlying issue here is that the pg_settings view doesn't show
> placeholder GUCs because we lack satisfactory values to put in
> most of the columns. I don't know if revisiting that conclusion
> would be appropriate or not. The purist approach would be to show
> NULL for any unknown column, but how many applications would that
> break? And even the "known" values could change unexpectedly when
> the module does get loaded, for example if the GUC has units and
> the value in the config file is expressed in a non-canonical way.
> (To say nothing of what a show hook might do...)

Perhaps the "category" could indicate that this is a placeholder value, and
the pg_settings documentation could explain exactly what that means (i.e.,
unknown to any libraries loaded in the current process, but may have
meaning to others).

--
Nathan Bossart
Amazon Web Services: https://aws.amazon.com