切换前enmo1为主库，enmo2为备库
[oracle@enmo1 admin]$ sqlplus / as sysdba
SQL*Plus: Release 11.2.0.4.0 Production on Sat May 6 10:14:57 2017
Copyright (c) 1982, 2013, Oracle. All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
查看主库的基本信息：
SYS@enmo1 hey~1->select open_mode,protection_mode,database_role,switchover_status from v$database;
OPEN_MODE PROTECTION_MODE DATABASE_ROLE SWITCHOVER_STATUS
-------------------- ----------------------------- ------------------------ ------------------------
READ WRITE MAXIMUM PERFORMANCE PRIMARY TO STANDBY
查看备库的基本信息：
SYS@enmo2 hey~2->select open_mode,protection_mode,database_role,switchover_status from v$database;
OPEN_MODE PROTECTION_MODE DATABASE_ROLE SWITCHOVER_STATUS
------------------------- ----------------------------- ------------------------ ------------------------
READ ONLY WITH APPLY MAXIMUM PERFORMANCE PHYSICAL STANDBY NOT ALLOWED
备库应用日志保持和主库数据一致（如果不一致，执行如下语句应用日志）
SYS@enmo2 hey~2->recover managed standby database using current logfile disconnect from session;
Media recovery complete.
SYS@enmo2 hey~2->recover managed standby database cancel;
Media recovery complete.
主库切换到备库角色并查看切换之后的状态为RECOVERY NEEDED
SYS@enmo1 hey~1->alter database commit to switchover to physical standby with session shutdown;
Database altered.
SYS@enmo1 hey~1->shutdown abort;
ORACLE instance started.
Total System Global Area 830930944 bytes
Fixed Size 2257800 bytes
Variable Size 700451960 bytes
Database Buffers 121634816 bytes
Redo Buffers 6586368 bytes
Database mounted.
SYS@enmo1 hey~1->select switchover_status from v$database;
SWITCHOVER_STATUS
--------------------
RECOVERY NEEDED
切换应用日志，然后在查看切换状态为TO primary正常：
SYS@enmo1 hey~1->recover managed standby database using current logfile disconnect from session;
Media recovery complete.
SYS@enmo1 hey~1->select switchover_status from v$database;
SWITCHOVER_STATUS
--------------------
TO PRIMARY
备库切主库：
SYS@enmo2 hey~2->select open_mode,protection_mode,database_role,switchover_status from v$database;
OPEN_MODE PROTECTION_MODE DATABASE_ROLE SWITCHOVER_STATUS
-------------------- -------------------- ---------------- --------------------
MOUNTED MAXIMUM PERFORMANCE PHYSICAL STANDBY TO PRIMARY
SYS@enmo2 hey~2->alter database commit to switchover to primary with session shutdown;
Database altered.
SYS@enmo2 hey~2->alter database open;
Database altered.
SYS@enmo2 hey~2->select switchover_status,database_role from v$database;
SWITCHOVER_STATUS DATABASE_ROLE
-------------------- ----------------
FAILED DESTINATION PRIMARY
SYS@enmo2 hey~2->select open_mode,protection_mode,database_role from v$database;
OPEN_MODE PROTECTION_MODE DATABASE_ROLE
-------------------- -------------------- ----------------
READ WRITE MAXIMUM PERFORMANCE PRIMARY