[Nathan Bossart <nathandbossart@gmail.com>]

On Thu, Jan 27, 2022 at 09:56:04AM +0900, Michael Paquier wrote:
> Hmm.  I have been looking at this patch, and the lack of centralized
> solution that could be used for other GUCs worries me like Fujii-san,
> even if this would prevent an incorrect use of MaxBackends in contexts
> where it should not be used because it is not initialized yet.  I
> don't think it is a good idea in the long-term to apply this as-is.

Alright.  I think the comment adjustments still apply, so I split those out
to a new patch.

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

Attachments:

v7-0001-Adjust-comments-about-registering-background-work.patch (text/x-diff, 2.6K) download
From 4bc21dc199616824b8f5790e8112ebf149f45207 Mon Sep 17 00:00:00 2001
From: Nathan Bossart <bossartn@amazon.com>
Date: Mon, 2 Aug 2021 17:42:25 +0000
Subject: [PATCH v7 1/1] Adjust comments about registering background workers
 before initializing MaxBackends.

Since 6bc8ef0b, InitializeMaxBackends() has used
max_worker_processes instead of tallying up the number of
registered background workers, so background worker registration is
no longer a prerequisite.  The ordering of this logic is still
useful for allowing libraries to adjust GUCs, so the comments have
been updated to mention that use-case.
---
 src/backend/postmaster/postmaster.c | 10 ++++------
 src/backend/utils/init/postinit.c   |  5 ++---
 2 files changed, 6 insertions(+), 9 deletions(-)

diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index dc4afdd75a..ac0ec0986a 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -1014,10 +1014,8 @@ PostmasterMain(int argc, char *argv[])
 	LocalProcessControlFile(false);
 
 	/*
-	 * Register the apply launcher.  Since it registers a background worker,
-	 * it needs to be called before InitializeMaxBackends(), and it's probably
-	 * a good idea to call it before any modules had chance to take the
-	 * background worker slots.
+	 * Register the apply launcher.  It's probably a good idea to call this
+	 * before any modules had a chance to take the background worker slots.
 	 */
 	ApplyLauncherRegister();
 
@@ -1038,8 +1036,8 @@ PostmasterMain(int argc, char *argv[])
 #endif
 
 	/*
-	 * Now that loadable modules have had their chance to register background
-	 * workers, calculate MaxBackends.
+	 * Now that loadable modules have had their chance to alter any GUCs,
+	 * calculate MaxBackends.
 	 */
 	InitializeMaxBackends();
 
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index d046caabd7..cd7c829ff5 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -483,9 +483,8 @@ pg_split_opts(char **argv, int *argcp, const char *optstr)
 /*
  * Initialize MaxBackends value from config options.
  *
- * This must be called after modules have had the chance to register background
- * workers in shared_preload_libraries, and before shared memory size is
- * determined.
+ * This must be called after modules have had the chance to alter GUCs in
+ * shared_preload_libraries and before shared memory size is determined.
  *
  * Note that in EXEC_BACKEND environment, the value is passed down from
  * postmaster to subprocesses via BackendParameters in SubPostmasterMain; only
-- 
2.25.1