From: Tom Lane <tgl@sss.pgh.pa.us>
To: guyren@relevantlogic.com
cc: pgsql-docs@lists.postgresql.org
Subject: Re: No discussion of custom variables;
 no "See also" for set_config, current_setting, pg_settings
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Comments: In-reply-to PG Doc comments form <noreply@postgresql.org>
	message dated "Fri, 02 Sep 2022 20:24:30 -0000"
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Date: Fri, 02 Sep 2022 18:16:09 -0400
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PG Doc comments form <noreply@postgresql.org> writes:
> A reader of this section
> https://www.postgresql.org/docs/current/sql-set.html of the documentation
> might be forgiven for thinking that Postgres does not support custom
> variables.

They are, in fact, *not* a supported feature.  The only intended use
of non-core GUCs was for extensions' parameters.  People have abused the
mechanism to create ad-hoc session variables, but we don't encourage it.
The underlying code won't scale to large numbers of variables, there's
no way to declare properties of such a variable in SQL, etc.

There's been an ongoing effort to create a respectable substitute,
but it still hasn't gotten across the finish line [1].

			regards, tom lane

[1] https://commitfest.postgresql.org/39/1608/