Logical replication

- Add PUBLICATION catalogs and DDL
- Add SUBSCRIPTION catalog and DDL
- Define logical replication protocol and output plugin
- Add logical replication workers

From: Petr Jelinek <petr@2ndquadrant.com>
Reviewed-by: Steve Singer <steve@ssinger.info>
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Erik Rijkers <er@xs4all.nl>
Reviewed-by: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>

src/backend/utils/misc/guc.c

@@ -59,6 +59,7 @@
 #include "postmaster/postmaster.h"
 #include "postmaster/syslogger.h"
 #include "postmaster/walwriter.h"
+#include "replication/logicallauncher.h"
 #include "replication/slot.h"
 #include "replication/syncrep.h"
 #include "replication/walreceiver.h"
@@ -2471,6 +2472,18 @@ static struct config_int ConfigureNamesInt[] =
 		check_max_worker_processes, NULL, NULL
 	},
 
+	{
+		{"max_logical_replication_workers",
+			PGC_POSTMASTER,
+			RESOURCES_ASYNCHRONOUS,
+			gettext_noop("Maximum number of logical replication worker processes."),
+			NULL,
+		},
+		&max_logical_replication_workers,
+		4, 0, MAX_BACKENDS,
+		NULL, NULL, NULL
+	},
+
 	{
 		{"log_rotation_age", PGC_SIGHUP, LOGGING_WHERE,
 			gettext_noop("Automatic log file rotation will occur after N minutes."),