Re: exposing pg_controldata and pg_config as functions

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On 08/20/2015 07:54 AM, Joe Conway wrote:
> On 08/20/2015 06:59 AM, Andrew Dunstan wrote:
>> I was a bit interested in pg_config information, for this reason:
>> I had a report of someone who had configured using --with-libxml
>> but the xml tests actually returned the results that are expected
>> without xml being configured. The regression tests thus passed,
>> but should not have. It occurred to me that if we had a test
>> like
>
>> select pg_config('configure') ~ '--with-libxml' as has_xml;
>
>> in the xml tests then this failure mode would be detected.
>
> I've found use for them both in the past. A fair amount of bit-rot
> has set it no doubt, and these were quick and dirty to begin with,
> but I have these hacks from a while back:
>
> https://github.com/jconway/pg_config

The attached implements pg_config as a backend SRF and a matching
system view. A few notes:

1) The syntax is a bit different than what Andrew proposed:

8<----------------
select setting ~ '--with-libxml' as has_xml
from pg_config
where name = 'CONFIGURE';
 has_xml
- ---------
 t
(1 row)
8<----------------

In particular note that the name values are all upper case to be
consistent with pg_config, and at least currently there is no version
of the function which accepts a name as an argument (didn't seem
worthwhile to me).

2) No docs or related regression test yet. I will do that if there is
enough interest in this getting committed. So far no one except Andrew
and I have chimed in.

3) Requires a catalog version bump (not in posted diff)

4) The static function cleanup_path() was borrowed from

    src/bin/pg_config/pg_config.c

It is a small and stable function (no change since 2010 AFAICS), so
maybe not worth the effort, but I was wondering if it should be moved
to src/common somewhere and shared.

I will add this to the next commitfest. Comments/feedback encouraged.

Joe

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