dataguard 添加级联节点

1，所有主机执行：
alter system set log_archive_config='dg_config=(ycloans,standbydb,xianzb,yunzhidb,zongbudb,xiandb)';

2，在中间数据开启日志传输
alter system set log_archive_dest_2='service=xiandb valid_for=(standby_logfile,standby_role) db_unique_name=xiandb';
alter system set log_archive_dest_state_2='enable';

3，启动日志应用进程
alter database recover managed standby database disconnect from session;

alter database recover managed standby database cancel;