Fix misleading comments about background worker registration.

robertmhaas · robertmhaas · commit 701d918a426b · 2022-05-06T09:24:06.000-04:00
Since 6bc8ef0, the maximum number of backends can't change as background workers are registered, but these comments still reflect the way things worked prior to that. Also, per recent discussion, some modules call SetConfigOption() from _PG_init(). It's not entirely clear to me whether we want to regard that as a fully supported operation, but since we know it's a thing that happens, it at least deserves a mention in the comments, so add that. Nathan Bossart, reviewed by Anton A. Melnikov Discussion: http://postgr.es/m/20220419154658.GA2487941@nathanxps13
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
@@ -1005,10 +1005,8 @@ 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();
 
@@ -1029,8 +1027,8 @@ 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
@@ -538,9 +538,8 @@ 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

Original file line number	Diff line number	Diff line change
`@@ -538,9 +538,8 @@ pg_split_opts(char *argv, int argcp, const char *optstr)`
`538`	`538`	`/*`
`539`	`539`	`* Initialize MaxBackends value from config options.`
`540`	`540`	`*`
`541`		`- * This must be called after modules have had the chance to register background`
`542`		`- * workers in shared_preload_libraries, and before shared memory size is`
`543`		`- * determined.`
	`541`	`+ * This must be called after modules have had the chance to alter GUCs in`
	`542`	`+ * shared_preload_libraries and before shared memory size is determined.`
`544`	`543`	`*`
`545`	`544`	`* Note that in EXEC_BACKEND environment, the value is passed down from`
`546`	`545`	`* postmaster to subprocesses via BackendParameters in SubPostmasterMain; only`