From: Tom Lane <tgl@sss.pgh.pa.us>
To: Ian Barwick <ian.barwick@2ndquadrant.com>
cc: Stephen Frost <sfrost@snowman.net>, Robert Haas <robertmhaas@gmail.com>,
        Tomas Vondra <tomas.vondra@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
In-reply-to: <54620b18-60b7-4b9b-7d1d-90a6464ab333@2ndquadrant.com>
References: 
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 <20190805172935.GK29202@tamriel.snowman.net>
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 <30179.1565029753@sss.pgh.pa.us>
 <CA+TgmoYEQyLE8Mtgko9-WSVWm=hLNGi3FO4xNLTrLpwi2GgPHw@mail.gmail.com>
 <30823.1565030571@sss.pgh.pa.us>
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 <32103.1565032053@sss.pgh.pa.us> <20190806005225.GM29202@tamriel.snowman.net>
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Comments: In-reply-to Ian Barwick <ian.barwick@2ndquadrant.com>
	message dated "Tue, 06 Aug 2019 14:53:10 +0900"
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Date: Tue, 06 Aug 2019 15:57:03 -0400
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Ian Barwick <ian.barwick@2ndquadrant.com> writes:
> On 8/6/19 11:16 AM, Stephen Frost wrote:
>>> Erm, those are duplicates though and we're saying that ALTER SYSTEM
>>> removes those...  Seems like we should be normalizing the file to be
>>> consistent in this regard too.

> True. (Switches brain on)... Ah yes, with the patch previously provided
> by Tom, it seems to be just a case of replacing "strcmp" with "guc_name_=
compare"
> to match the existing string; the name will be rewritten with the value =
provided
> to ALTER SYSTEM, which will be normalized to lower case anyway.

Good catch.

>>> I dislike the special-casing of ALTER SYSTEM here, where we're basical=
ly
>>> saying that only ALTER SYSTEM is allowed to do this cleanup and that i=
f
>>> such cleanup is wanted then ALTER SYSTEM must be run.

> This is just saying what ALTER SYSTEM will do, which IMHO we should desc=
ribe
> somewhere. Initially when I stated working with pg.auto.conf I had
> my application append a comment line to show where the entries came from=
,
> but not having any idea how pg.auto.conf was modified at that point, I w=
as
> wondering why the comment subsequently disappeared. Perusing the source =
code has
> explained that for me, but would be mighty useful to document that.

I feel fairly resistant to making the config.sgml explanation much longer
than what I wrote.  That chapter is material that every Postgres DBA has
to absorb, so we should *not* be burdening it with stuff that few people
need to know.

Perhaps we could put some of these details into the Notes section of the
ALTER SYSTEM ref page.  But I wonder how much of this is needed at all.

			regards, tom lane