Check that there is no exclusive backup taking place while we perform

a switchover.

We've found that this can cause some issues with postgres control
metadata (could be a postgres bug) so best thing is *not* no switchover
if there's a backup taking place.

It's also a bad idea from an architectual point of view, as a switchover
is supposed to be planed, so why perform it when we are taking backups.

GitHub #476.

dbutils.c

@@ -3953,7 +3953,31 @@ connection_ping(PGconn *conn)
 	return;
 }
 
+/*
+ * Function that checks if the primary is in exclusive backup mode.
+ * We'll use this when executing an action can conflict with an exclusive
+ * backup.
+ */
+bool
+server_not_in_exclusive_backup_mode(PGconn *conn)
+{
+	PGresult   *res = PQexec(conn, "SELECT pg_is_in_backup()");
 
+	if (PQresultStatus(res) != PGRES_TUPLES_OK)
+	{
+		log_error(_("unable to retrieve information regarding backup mode of node"));
+		log_detail("%s", PQerrorMessage(conn));
+		PQclear(res);
+		return false;
+	}
+
+	if (strcmp(PQgetvalue(res, 0, 0), "t") == 0)
+	{
+		log_warning(_("node is in exclusive backup mode"));
+		return false;
+	}
+	return true;
+}
 
 /* ==================== */
 /* monitoring functions */

dbutils.h

@@ -467,6 +467,7 @@ int			wait_connection_availability(PGconn *conn, long long timeout);
 bool		is_server_available(const char *conninfo);
 bool		is_server_available_params(t_conninfo_param_list *param_list);
 void		connection_ping(PGconn *conn);
+bool            server_not_in_exclusive_backup_mode(PGconn *conn);
 
 /* monitoring functions  */
 void

repmgr-action-standby.c

@@ -2911,6 +2911,24 @@ do_standby_switchover(void)
 		exit(ERR_DB_QUERY);
 	}
 
+	/*
+	 * Check that there's no exclusive backups running on the primary.
+	 * We don't want to end up damaging the backup and also leaving the server in an
+	 * state where there's control data saying it's in backup mode but there's no
+	 * backup_label in PGDATA.
+	 * If the DBA wants to do the switchover anyway, he should first stop the
+	 * backup that's running.
+	 */
+	if (!server_not_in_exclusive_backup_mode(remote_conn))
+	{
+		log_error(_("can't perform a switchover while primary server is in exclusive backup mode"));
+		log_hint(_("stop backup before attempting the switchover"));
+
+		PQfinish(remote_conn);
+
+		exit(ERR_SWITCHOVER_FAIL);
+	}
+
 	/*
 	 * Check this standby is attached to the demotion candidate
 	 * TODO: