Message-ID: <19600510deacf21b05a2c76bc3bde8d1283c77e3.camel@cybertec.at>
Subject: Re: "20.16. Customized Options" =?UTF-8?Q?=E2=80=93=C2=A0cannot?=
 be set by `ALTER SYSTEM`
From: Laurenz Albe <laurenz.albe@cybertec.at>
To: Tom Lane <tgl@sss.pgh.pa.us>, gavinpanella@gmail.com
Cc: pgsql-docs@lists.postgresql.org
Date: Mon, 16 Oct 2023 19:37:46 +0200
In-Reply-To: <2307198.1697473749@sss.pgh.pa.us>
References: 
	<169746329791.169914.16613647309012285391@wrigleys.postgresql.org>
	 <2307198.1697473749@sss.pgh.pa.us>
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On Mon, 2023-10-16 at 12:29 -0400, Tom Lane wrote:
> I do see an issue here:
>=20
> regression=3D# ALTER SYSTEM SET foo.bar TO 'baz';
> ERROR:=C2=A0 unrecognized configuration parameter "foo.bar"
> regression=3D# SET foo.bar TO 'baz';
> SET
> regression=3D# ALTER SYSTEM SET foo.bar TO 'baz';
> ALTER SYSTEM
>=20
> and now we have
>=20
> $ cat $PGDATA/postgresql.auto.conf
> # Do not edit this file manually!
> # It will be overwritten by the ALTER SYSTEM command.
> foo.bar =3D 'baz'
>=20
> So that feels like a bug: we should not allow ALTER SYSTEM to execute
> against a placeholder GUC definition, because the placeholder can't
> tell us whether the value is valid.=C2=A0 I wonder though if forbidding
> this would break any legitimate usage patterns.

I feel the same.  However, the lack of any "variables" in SQL (as proposed
in [1]) leads a lot of people to abuse placeholder parameters as variables
to hold application state.  I am sure that that is where this complaint
comes from.  We maintain that doing so is not a valid use case, but that cl=
aim
sounds increasingly like a grammarian declaring that sentences should not
end with a preposition, when everybody does it all the time.

Yours,
Laurenz Albe

 [1]: https://postgr.es/m/CAFj8pRDY%2Bm9OOxfO10R7J0PAkCCauM-TweaTrdsrsLGMb1=
VbEQ%40mail.gmail.com