DG主备切换主要说明

1. alter system switch logfile; 切换主库日志
2. select max(sequence#) from v$archived_log; 对比主备库日志，同步才能做下一步
3. alter database commit to switchover to standby with session shutdown; 有用户登录，主库强制切换
4. 主备库都重启到 mount状态下，备库执行转换命令 ；alter database commit to switchover to primary
5. alter database open; 备库打开库，然后主库打开库
6. recover managed standby database disconnect from session; 主库执行MRP进程恢复
7. select name,open_mode,database_role,protection_mode,switchover_status from v$database; 俩库都检查
8. 主备切换完成