Make self-referencing foreign key on repl_nodes table deferrable

dbutils.c

@@ -1127,6 +1127,21 @@ witness_copy_node_records(PGconn *masterconn, PGconn *witnessconn, char *cluster
 
 	begin_transaction(witnessconn);
 
+	/* Defer constraints */
+	sqlquery_snprintf(sqlquery, "SET CONSTRAINTS ALL DEFERRED;");
+	log_verbose(LOG_DEBUG, "witness_copy_node_records():\n%s\n", sqlquery);
+
+	res = PQexec(witnessconn, sqlquery);
+	if (!res || PQresultStatus(res) != PGRES_COMMAND_OK)
+	{
+		log_err(_("Unable to defer constraints:\n%s\n"),
+				PQerrorMessage(witnessconn));
+		rollback_transaction(witnessconn);
+
+		return false;
+	}
+
+	/* Truncate existing records */
 	sqlquery_snprintf(sqlquery, "TRUNCATE TABLE %s.repl_nodes", get_repmgr_schema_quoted(witnessconn));
 
 	log_verbose(LOG_DEBUG, "witness_copy_node_records():\n%s\n", sqlquery);
@@ -1136,9 +1151,12 @@ witness_copy_node_records(PGconn *masterconn, PGconn *witnessconn, char *cluster
 	{
 		log_err(_("Unable to truncate witness servers's repl_nodes table:\n%s\n"),
 				PQerrorMessage(witnessconn));
+		rollback_transaction(witnessconn);
+
 		return false;
 	}
 
+	/* Get current records from primary */
 	sqlquery_snprintf(sqlquery,
 					  "SELECT id, type, upstream_node_id, name, conninfo, priority, slot_name, active FROM %s.repl_nodes",
 					  get_repmgr_schema_quoted(masterconn));
@@ -1156,6 +1174,7 @@ witness_copy_node_records(PGconn *masterconn, PGconn *witnessconn, char *cluster
 		return false;
 	}
 
+	/* Insert primary records into witness table */
 	for (i = 0; i < PQntuples(res); i++)
 	{
 		bool node_record_created;
@@ -1197,6 +1216,7 @@ witness_copy_node_records(PGconn *masterconn, PGconn *witnessconn, char *cluster
 	}
 	PQclear(res);
 
+	/* And finished */
 	commit_transaction(witnessconn);
 
 	return true;

repmgr.c

@@ -4505,7 +4505,7 @@ create_schema(PGconn *conn)
 					  "CREATE TABLE %s.repl_nodes (     "
 					  "  id               INTEGER PRIMARY KEY, "
 					  "  type             TEXT    NOT NULL CHECK (type IN('master','standby','witness')), "
-					  "  upstream_node_id INTEGER NULL REFERENCES %s.repl_nodes (id), "
+					  "  upstream_node_id INTEGER NULL REFERENCES %s.repl_nodes (id) DEFERRABLE, "
 					  "  cluster          TEXT    NOT NULL, "
 					  "  name             TEXT    NOT NULL, "
 					  "  conninfo         TEXT    NOT NULL, "

sql/repmgr3.1.1_repmgr3.1.2.sql

@@ -0,0 +1,31 @@
+/*
+ * Update a repmgr 3.1.1 installation to repmgr 3.1.2
+ * --------------------------------------------------
+ *
+ * This update is only required if repmgrd is being used in conjunction
+ * with a witness server.
+ *
+ * The new repmgr package should be installed first. Then
+ * carry out these steps:
+ *
+ *   1. (If repmgrd is used) stop any running repmgrd instances
+ *   2. On the master node, execute the SQL statement listed below
+ *   3. (If repmgrd is used) restart repmgrd
+ */
+
+/*
+ * If your repmgr installation is not included in your repmgr
+ * user's search path, please set the search path to the name
+ * of the repmgr schema to ensure objects are installed in
+ * the correct location.
+ *
+ * The repmgr schema is  "repmgr_" + the cluster name defined in
+ * 'repmgr.conf'.
+ */
+
+-- SET search_path TO 'name_of_repmgr_schema';
+
+BEGIN;
+
+ALTER TABLE repl_nodes ALTER CONSTRAINT repl_nodes_upstream_node_id_fkey DEFERRABLE;
+COMMIT;