Date: Mon, 9 May 2022 15:53:24 +0900
From: Michael Paquier <michael@paquier.xyz>
To: Nathan Bossart <nathandbossart@gmail.com>
Cc: Magnus Hagander <magnus@hagander.net>,
	"Bossart, Nathan" <bossartn@amazon.com>,
	Fujii Masao <masao.fujii@oss.nttdata.com>,
	Justin Pryzby <pryzby@telsasoft.com>,
	Andres Freund <andres@anarazel.de>,
	Mark Dilger <mark.dilger@enterprisedb.com>,
	Don Seiler <don@seiler.us>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: Estimating HugePages Requirements?
Message-ID: <Yni6ZHkGotUU+RSf@paquier.xyz>
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 <20220315224439.GA1133771@nathanxps13>
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On Fri, May 06, 2022 at 10:13:18AM -0700, Nathan Bossart wrote:
> On Tue, Apr 26, 2022 at 10:34:06AM +0900, Michael Paquier wrote:
>> Yes, the redirection issue would apply to all the run-time GUCs.
>=20
> Should this be tracked as an open item for v15?  There was another recent
> report about the extra log output [0].

That makes it for two complaints on two separate threads.  So an open
item seems adapted to adjust this behavior.

I have looked at the patch posted at [1], and I don't quite understand
why you need the extra dance with log_min_messages.  Why don't you
just set the GUC at the end of the code path in PostmasterMain() where
we print non-runtime-computed parameters?  I am not really worrying
about users deciding to set log_min_messages to PANIC in
postgresql.conf when it comes to postgres -C, TBH, as they'd miss the
FATAL messages if the command is attempted on a server already
starting.

Per se the attached.

[1]: https://www.postgresql.org/message-id/20220328173503.GA137769@nathanxp=
s13
--
Michael

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=46rom 3b8a7f8079955cd59a5a318adf6938cdd3c29c6b Mon Sep 17 00:00:00 2001
=46rom: Michael Paquier <michael@paquier.xyz>
Date: Mon, 9 May 2022 15:50:19 +0900
Subject: [PATCH v4] Silence extra logging with 'postgres -C'.

Presently, the server may emit a variety of extra log messages when
inspecting GUC values.  For example, when inspecting a runtime-computed
GUC, the server will always emit a "database system is shut down" LOG
(unless the user has set log_min_messages higher than LOG).  To avoid
these extra log messages, this change sets log_min_messages to FATAL
when -C is used (even if set to PANIC in postgresql.conf).  At FATAL,
the user will still receive messages explaining why a GUC's value cannot
be inspected.
---
 src/backend/postmaster/postmaster.c | 10 ++++++++++
 doc/src/sgml/runtime.sgml           |  2 +-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/p=
ostmaster.c
index ce4007bb2c..38b63bc215 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -913,6 +913,16 @@ PostmasterMain(int argc, char *argv[])
 			puts(config_val ? config_val : "");
 			ExitPostmaster(0);
 		}
+
+		/*
+		 * A runtime-computed GUC will be printed later on.  As we initialize
+		 * a server startup sequence, silence any log messages that may show up
+		 * in the output generated.  FATAL and more severe messages are useful
+		 * to show, even if one would only expect at least PANIC.  LOG entries
+		 * are hidden.
+		 */
+		SetConfigOption("log_min_messages", "FATAL", PGC_INTERNAL,
+						PGC_S_OVERRIDE);
 	}
=20
 	/* Verify that DataDir looks reasonable */
diff --git a/doc/src/sgml/runtime.sgml b/doc/src/sgml/runtime.sgml
index 4465c876b1..62cec614d3 100644
--- a/doc/src/sgml/runtime.sgml
+++ b/doc/src/sgml/runtime.sgml
@@ -1448,7 +1448,7 @@ export PG_OOM_ADJUST_VALUE=3D0
     server must be shut down to view this runtime-computed parameter.
     This might look like:
 <programlisting>
-$ <userinput>postgres -D $PGDATA -C shared_memory_size_in_huge_pages 2> /d=
ev/null</userinput>
+$ <userinput>postgres -D $PGDATA -C shared_memory_size_in_huge_pages</user=
input>
 3170
 $ <userinput>grep ^Hugepagesize /proc/meminfo</userinput>
 Hugepagesize:       2048 kB
--=20
2.36.0


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