From: Tom Lane <tgl@sss.pgh.pa.us>
To: Stephen Frost <sfrost@snowman.net>
cc: Robert Haas <robertmhaas@gmail.com>,
        Ian Barwick <ian.barwick@2ndquadrant.com>,
        Amit Kapila <amit.kapila16@gmail.com>,
        "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Subject: Re: [PATCH] Stop ALTER SYSTEM from making bad assumptions
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Comments: In-reply-to Stephen Frost <sfrost@snowman.net>
	message dated "Fri, 21 Jun 2019 12:40:28 -0400"
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Date: Fri, 21 Jun 2019 12:55:12 -0400
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Stephen Frost <sfrost@snowman.net> writes:
> * Tom Lane (tgl@sss.pgh.pa.us) wrote:
>> I haven't been paying too close attention to this thread, but isn't
>> that exactly what it does now and always has?  guc.c, at least, certainly
>> is going to interpret duplicate entries that way.

> The issue isn't with reading them and interpreting them, it's what
> happens when you run ALTER SYSTEM and it goes and modifies the file.
> Presently, it basically operates on the first entry it finds when
> performing a SET or a RESET.

Ah, got it.  So it seems like the correct behavior might be for
ALTER SYSTEM to
(a) run through the whole file and remove any conflicting lines;
(b) append new setting at the end.

If you had some fancy setup with comments associated with entries,
you might not be pleased with that.  But I can't muster a lot of
sympathy for tools putting comments in postgresql.auto.conf anyway;
it's not intended to be a human-readable file.

If anybody does complain, my first reaction would be to make ALTER
SYSTEM strip all comment lines too.

			regards, tom lane