Date: Thu, 13 Oct 2022 11:24:08 -0700
From: Nathan Bossart <nathandbossart@gmail.com>
To: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Cc: Peter Eisentraut <peter.eisentraut@enterprisedb.com>,
	Tom Lane <tgl@sss.pgh.pa.us>,
	Benoit =?iso-8859-1?Q?Lobr=E9au?= <benoit.lobreau@gmail.com>,
	Alvaro Herrera <alvherre@alvh.no-ip.org>,
	Robert Haas <robertmhaas@gmail.com>,
	"Bossart, Nathan" <bossartn@amazon.com>,
	David Steele <david@pgmasters.net>,
	Fujii Masao <masao.fujii@oss.nttdata.com>,
	"pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>,
	Michael Paquier <michael@paquier.xyz>,
	Magnus Hagander <magnus@hagander.net>,
	Stephen Frost <sfrost@snowman.net>
Subject: Re: archive modules
Message-ID: <20221013182408.GA1551106@nathanxps13>
References: <2884265.1663188443@sss.pgh.pa.us>
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 <20220914222736.GA3042279@nathanxps13>
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 <20220923161402.GA736566@nathanxps13>
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On Thu, Oct 13, 2022 at 03:25:27PM +0530, Bharath Rupireddy wrote:
> The intent here looks reasonable to me. However, why should the user
> be able to set both archive_command and archive_library in the first
> place only to later fail in LoadArchiveLibrary() per the patch? IMO,
> the check_hook() is the right way to disallow any sorts of GUC
> misconfigurations, no?

There was some discussion upthread about using the GUC hooks to enforce
this [0].  In general, it doesn't seem to be a recommended practice.  One
basic example of the problems with this approach is the following:

  1. Set archive_command and leave archive_library unset and restart
     the server.
  2. Unset archive_command and set archive_library and call 'pg_ctl
     reload'.

After these steps, you'll see the following log messages:

	2022-10-13 10:58:42.112 PDT [1562524] LOG:  received SIGHUP, reloading configuration files
	2022-10-13 10:58:42.114 PDT [1562524] LOG:  cannot set "archive_library" when "archive_command" is specified
	2022-10-13 10:58:42.114 PDT [1562524] DETAIL:  Only one of "archive_library" or "archive_command" can be specified.
	2022-10-13 10:58:42.114 PDT [1562524] LOG:  parameter "archive_command" changed to ""
	2022-10-13 10:58:42.114 PDT [1562524] LOG:  configuration file "/home/nathan/pgdata/postgresql.conf" contains errors; unaffected changes were applied

[0] https://postgr.es/m/20220914200305.GA2984249%40nathanxps13

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com