Date: Wed, 5 Oct 2022 11:57:16 -0700
From: Nathan Bossart <nathandbossart@gmail.com>
To: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Cc: 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: <20221005185716.GB201192@nathanxps13>
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 <20220914211746.GA2986134@nathanxps13>
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 <20220914222736.GA3042279@nathanxps13>
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On Wed, Oct 05, 2022 at 07:55:58PM +0200, Peter Eisentraut wrote:
> Leaving archive_command empty is an intentional configuration choice.
> 
> What we are talking about here is, arguably, a misconfiguration, so it
> should result in an error.

Okay.  What do you think about something like the attached?

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

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diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index d750290f13..bb4d985f35 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -3597,9 +3597,11 @@ include_dir 'conf.d'
        </para>
        <para>
         This parameter can only be set in the <filename>postgresql.conf</filename>
-        file or on the server command line.  It is ignored unless
+        file or on the server command line.  It is only used if
         <varname>archive_mode</varname> was enabled at server start and
-        <varname>archive_library</varname> is set to an empty string.
+        <varname>archive_library</varname> is set to an empty string.  If both
+        <varname>archive_command</varname> and <varname>archive_library</varname>
+        are set, archiving will fail.
         If <varname>archive_command</varname> is an empty string (the default) while
         <varname>archive_mode</varname> is enabled (and <varname>archive_library</varname>
         is set to an empty string), WAL archiving is temporarily
@@ -3624,7 +3626,9 @@ include_dir 'conf.d'
        <para>
         The library to use for archiving completed WAL file segments.  If set to
         an empty string (the default), archiving via shell is enabled, and
-        <xref linkend="guc-archive-command"/> is used.  Otherwise, the specified
+        <xref linkend="guc-archive-command"/> is used.  If both
+        <varname>archive_command</varname> and <varname>archive_library</varname>
+        are set, archiving will fail.  Otherwise, the specified
         shared library is used for archiving.  For more information, see
         <xref linkend="backup-archiving-wal"/> and
         <xref linkend="archive-modules"/>.
diff --git a/src/backend/postmaster/pgarch.c b/src/backend/postmaster/pgarch.c
index 3868cd7bd3..56dcc0dce5 100644
--- a/src/backend/postmaster/pgarch.c
+++ b/src/backend/postmaster/pgarch.c
@@ -838,6 +838,12 @@ LoadArchiveLibrary(void)
 
 	memset(&ArchiveContext, 0, sizeof(ArchiveModuleCallbacks));
 
+	if (XLogArchiveLibrary[0] != '\0' && XLogArchiveCommand[0] != '\0')
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				 errmsg("both archive_command and archive_library specified"),
+				 errdetail("Only one of archive_command, archive_library may be set.")));
+
 	/*
 	 * If shell archiving is enabled, use our special initialization function.
 	 * Otherwise, load the library and call its _PG_archive_module_init().

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