Fix comments about bgworker registration before MaxBackends initialization

michaelpq · michaelpq · commit 5ecd0183fb6a · 2022-01-29T10:47:36.000+09:00
Since 6bc8ef0, InitializeMaxBackends() has used max_worker_processes instead of adapting MaxBackends to the number of background workers registered by modules loaded in shared_preload_libraries (at this time, bgworkers were only static, but gained dynamic capabilities as a matter of supporting parallel queries meaning that a control cap was necessary). Some comments referred to the past registration logic, making them confusing and incorrect, so fix these. Some of the out-of-core modules that could be loaded in this path sometimes like to manipulate dynamically some of the resource-related GUCs for their own needs, this commit adds a note about that. Author: Nathan Bossart Discussion: https://postgr.es/m/20220127181815.GA551692@nathanxps13
diff --git 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
@@ -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

Original file line number	Diff line number	Diff line change
`@@ -483,9 +483,8 @@ pg_split_opts(char *argv, int argcp, const char *optstr)`
`483`	`483`	`/*`
`484`	`484`	`* Initialize MaxBackends value from config options.`
`485`	`485`	`*`
`486`		`- * This must be called after modules have had the chance to register background`
`487`		`- * workers in shared_preload_libraries, and before shared memory size is`
`488`		`- * determined.`
	`486`	`+ * This must be called after modules have had the chance to alter GUCs in`
	`487`	`+ * shared_preload_libraries and before shared memory size is determined.`
`489`	`488`	`*`
`490`	`489`	`* Note that in EXEC_BACKEND environment, the value is passed down from`
`491`	`490`	`* postmaster to subprocesses via BackendParameters in SubPostmasterMain; only`