calculate-MaxBackends-in-postmaster.patch

diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index 8f39aec..9dc8bd3 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -499,6 +499,7 @@ typedef struct
 	bool		redirection_done;
 	bool		IsBinaryUpgrade;
 	int			max_safe_fds;
+	int			MaxBackends;
 #ifdef WIN32
 	HANDLE		PostmasterHandle;
 	HANDLE		initial_signal_pipe;
@@ -897,15 +898,11 @@ PostmasterMain(int argc, char *argv[])
 	process_shared_preload_libraries();
 
 	/*
-	 * If loadable modules have added background workers, MaxBackends needs to
-	 * be updated.	Do so now by forcing a no-op update of max_connections.
-	 * XXX This is a pretty ugly way to do it, but it doesn't seem worth
-	 * introducing a new entry point in guc.c to do it in a cleaner fashion.
+	 * Now that loadable modules have had their chance to register background
+	 * workers, calculate MaxBackends.
 	 */
-	if (GetNumShmemAttachedBgworkers() > 0)
-		SetConfigOption("max_connections",
-						GetConfigOption("max_connections", false, false),
-						PGC_POSTMASTER, PGC_S_OVERRIDE);
+	MaxBackends = MaxConnections + autovacuum_max_workers + 1 +
+		GetNumShmemAttachedBgworkers();
 
 	/*
 	 * Establish input sockets.
@@ -5836,6 +5833,8 @@ save_backend_variables(BackendParameters *param, Port *port,
 	param->IsBinaryUpgrade = IsBinaryUpgrade;
 	param->max_safe_fds = max_safe_fds;
 
+	param->MaxBackends = MaxBackends;
+
 #ifdef WIN32
 	param->PostmasterHandle = PostmasterHandle;
 	if (!write_duplicated_handle(&param->initial_signal_pipe,
@@ -6061,6 +6060,8 @@ restore_backend_variables(BackendParameters *param, Port *port)
 	IsBinaryUpgrade = param->IsBinaryUpgrade;
 	max_safe_fds = param->max_safe_fds;
 
+	MaxBackends = param->MaxBackends;
+
 #ifdef WIN32
 	PostmasterHandle = param->PostmasterHandle;
 	pgwin32_initial_signal_pipe = param->initial_signal_pipe;
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 2cf34ce..eca6a60 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -199,9 +199,7 @@ static const char *show_tcp_keepalives_idle(void);
 static const char *show_tcp_keepalives_interval(void);
 static const char *show_tcp_keepalives_count(void);
 static bool check_maxconnections(int *newval, void **extra, GucSource source);
-static void assign_maxconnections(int newval, void *extra);
 static bool check_autovacuum_max_workers(int *newval, void **extra, GucSource source);
-static void assign_autovacuum_max_workers(int newval, void *extra);
 static bool check_effective_io_concurrency(int *newval, void **extra, GucSource source);
 static void assign_effective_io_concurrency(int newval, void *extra);
 static void assign_pgstat_temp_directory(const char *newval, void *extra);
@@ -1615,7 +1613,7 @@ static struct config_int ConfigureNamesInt[] =
 		},
 		&MaxConnections,
 		100, 1, MAX_BACKENDS,
-		check_maxconnections, assign_maxconnections, NULL
+		check_maxconnections, NULL, NULL
 	},
 
 	{
@@ -2290,7 +2288,7 @@ static struct config_int ConfigureNamesInt[] =
 		},
 		&autovacuum_max_workers,
 		3, 1, MAX_BACKENDS,
-		check_autovacuum_max_workers, assign_autovacuum_max_workers, NULL
+		check_autovacuum_max_workers, NULL, NULL
 	},
 
 	{
@@ -8636,13 +8634,6 @@ check_maxconnections(int *newval, void **extra, GucSource source)
 	return true;
 }
 
-static void
-assign_maxconnections(int newval, void *extra)
-{
-	MaxBackends = newval + autovacuum_max_workers + 1 +
-		GetNumShmemAttachedBgworkers();
-}
-
 static bool
 check_autovacuum_max_workers(int *newval, void **extra, GucSource source)
 {
@@ -8652,12 +8643,6 @@ check_autovacuum_max_workers(int *newval, void **extra, GucSource source)
 	return true;
 }
 
-static void
-assign_autovacuum_max_workers(int newval, void *extra)
-{
-	MaxBackends = MaxConnections + newval + 1 + GetNumShmemAttachedBgworkers();
-}
-
 static bool
 check_effective_io_concurrency(int *newval, void **extra, GucSource source)
 {