Date: Sun, 16 Jun 2019 13:43:32 -0400
From: Stephen Frost <sfrost@snowman.net>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Amit Kapila <amit.kapila16@gmail.com>,
	Ian Barwick <ian.barwick@2ndquadrant.com>,
	"pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Subject: Re: [PATCH] Stop ALTER SYSTEM from making bad assumptions
Message-ID: <20190616174332.GR2480@tamriel.snowman.net>
References: <aed6cc9f-98f3-2693-ac81-52bb0052307e@2ndquadrant.com>
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Greetings,

* Tom Lane (tgl@sss.pgh.pa.us) wrote:
> Stephen Frost <sfrost@snowman.net> writes:
> > Unless there's actually a use-case for duplicate entries in
> > postgresql.auto.conf,
>=20
> There isn't --- guc.c will just discard the earlier duplicates.

One might be able to argue for trying to create a stack or some such, to
allow you to more easily move between values or to see what the value
was set to at some point in the past, etc etc.  Until we see an actual
thought out use-case along those lines that requires supporting
duplicates in some fashion though, with code to make it all work, I
don't think we should allow it.

> > what we should do is clean them up (and possibly
> > throw a WARNING or similar at the user saying "something modified your
> > postgresql.auto.conf in an unexpected way").  I'd suggest we do that on
> > every ALTER SYSTEM call.
>=20
> +1 for having ALTER SYSTEM clean out duplicates.  Not sure whether
> a WARNING would seem too in-your-face.

I'd hope for a warning from basically every part of the system when it
detects, clearly, that a file was changed in a way that it shouldn't
have been.  If we don't throw a warning, then we're implying that it's
acceptable, but then cleaning up the duplicates, which seems pretty
confusing.

Thanks,

Stephen

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