问题描述：备库恢复DG之后，mrp进程一直是wait_for_log，主库创建数据没有正常同步，只有在切换归档的时候备库才能同步主库数据
查看主库日志，主库RFS进程提示没有可用的standby redo在线程1上
主库输出日志：
RFS[3]: Assigned to RFS process 15362 RFS[3]: No standby redo logfiles available for thread 1 RFS[3]: Opened log for thread 1 sequence 712 dbid 1446616449 branch 1051207668 Sat Apr 24 10:19:52 2021
查询主备库standby_log大小
主库：
SQL> select group#,thread#,sequence#,bytes/1024/1024 from v$Log;
GROUP# THREAD# SEQUENCE# BYTES/1024/1024
---------- ---------- ---------- ---------------
1 1 709 512
2 1 710 512
3 1 711 512
4 1 712 512
5 1 707 512
6 1 708 512
备库：
SQL> select group#,thread#,sequence#,bytes/1024/1024 from v$standby_log;
GROUP# THREAD# SEQUENCE# BYTES/1024/1024
---------- ---------- ---------- ---------------
30 1 0 500
31 1 0 500
32 1 0 500
33 1 0 500
34 1 0 500
38 1 0 500
39 1 0 500
经比较主备库standby_log大小创建不一致，重建备库standby_log
alter database add standby logfile thread 1 group 48‘/data/orcl/std_redo48.log‘ size 512M; alter database add standby logfile thread 1 group 49‘/data/orcl/std_redo49.log‘ size 512M; alter database add standby logfile thread 1 group 40‘/data/orcl/std_redo40.log‘ size 512M; alter database add standby logfile thread 1 group 41‘/data/orcl/std_redo41.log‘ size 512M; alter database add standby logfile thread 1 group 42‘/data/orcl/std_redo42.log‘ size 512M; alter database add standby logfile thread 1 group 43‘/data/orcl/std_redo43.log‘ size 512M; alter database add standby logfile thread 1 group 44‘/data/orcl/std_redo44.log‘ size 512M; alter database drop logfile group 38; alter database drop logfile group 39; alter database drop logfile group 30; alter database drop logfile group 31; alter database drop logfile group 32; alter database drop logfile group 33; alter database drop logfile group 34;
主库切换归档测试
alter system switch logfile;
备库：
SQL> select process, status, thread#,sequence#, block#, blocks from v$managed_standby; PROCESS STATUS THREAD# SEQUENCE# BLOCK# BLOCKS --------- ------------ ---------- ---------- ---------- ---------- ARCH CONNECTED 0 0 0 0 ARCH CONNECTED 0 0 0 0 ARCH CONNECTED 0 0 0 0 ARCH CLOSING 1 710 1 416 RFS IDLE 0 0 0 0 MRP0 APPLYING_LOG 1 713 255005 1048576 RFS IDLE 0 0 0 0 RFS IDLE 1 713 255005 1 8 rows selected.
状态正常，mrp进程已经变成applying_log