记一次ADG恢复

生产搭建的读写分离ADG，一不小心备库磁盘空间满了，删除了一些已经应用过的归档日志，开始恢复ADG With Real-time Query
1. 先查看有无归档日志gap
SQL> select thread#, low_sequence#, high_sequence# from v$archive_gap;
SQL> select thread#, sequence#, first_time, name, applied from v$archived_log where order by sequence#;
如果有归档日志没有拷贝到备库，可以手动拷贝一下。

2. SQL> shutdown immediate;

3. SQL> startup nomount;

4. SQL> alter database mount standby database;
这一步可能报错：ora-16136，表示托管备库恢复进程并未运行
检查MRP进程状态：
SQL> select process, status, thread#, sequence#, block# from v$managed_standby where process = 'MRP' or process = 'MRP0';
如果查询没有返回任何结果，说明MRP进程确实没有运行，这就是报错的原因
启动实时应用：
SQL> alter database recover managed standby database using current logfile disconnect from session;
disconnect from session的作用是：让恢复进程在后台独立运行，与当前会话断开连接。
如果没有 disconnect from session，恢复进程会绑定到当前会话，如果你退出SQL*Plus或断开当前会话连接，恢复进程会自动停止
再次检查MRP进程状态：
SQL> select process, status, thread#, sequence#, block# from v$managed_standby where process = 'MRP' or process = 'MRP0';

5. SQL> alter database open;

6. SQL> alter database recover managed standby database using current logfile disconnect from session;
using current logfile的作用是：备库收到日志后，实时完成恢复，这里的日志是redo log file

7. SQL> select open_mode from v$database;
READ ONLY WITH APPLY
备库恢复完成！