Re: Why don't custom GUCs show in pg_settings?

On Sat, Apr 30, 2016 at 9:39 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> "David G. Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> writes:
> > I've seen and can work with various work-arounds but it seems odd that
> > pg_settings doesn't show these custom GUCs.
>
> Because we don't know what type they should be.
>
> If we're ever to support custom GUCs properly, rather than as a hack that
> accidentally sorta works, there needs to be a way to declare them and
> establish their properties; whereupon there would be info for pg_settings
> to display.
>

​It seems that a "reasonable defaults"​ policy would be better than
nothing...though given the "missing_ok" feature the work-around with
pg_settings isn't needed.

​The existing set_config would setup the text-oriented defaults while, if
someone cares enough, a set_custom_config (or overloaded set_config)
function could be written that would allow specifying​ stuff like
description, unit, initial value, etc.

But what amounts to a session-local hstore seem, whose contents are
displayed in pg_settings along with the system GUCs, and is documented,
seems like an adequate feature to acknowledge officially.

> > Is there a simple way to read the value without receiving an error if the
> > value is missing?
>
> See 10fb48d66, which I don't particularly approve of because it piled
> another hack on top of that mess without doing a thing to make it cleaner.
>

​Thanks.

I recalled seeing that, just didn't remember that it is new to 9.6 - I
only looked at the 9.5 documentation and didn't see it.

David J.​