1.首先要应用日志，保持主备库一致：
备库：SBDB@SYS> recover managed standby database using current logfile disconnect from session;
Media recovery complete.
2.查看主备状态：
（1）主库：
ORA11GR2@SYS> select open_mode,protection_mode,database_role,switchover_status from v$database; OPEN_MODE PROTECTION_MODE DATABASE_ROLE SWITCHOVER_STATUS
-------------------- -------------------- ---------------- --------------------
READ WRITE MAXIMUM PERFORMANCE PRIMARY SESSIONS ACTIVE （2）备库：
SBDB@SYS> select open_mode,protection_mode,database_role,switchover_status from v$database; OPEN_MODE PROTECTION_MODE DATABASE_ROLE SWITCHOVER_STATUS
-------------------- -------------------- ---------------- --------------------
READ ONLY MAXIMUM PERFORMANCE PHYSICAL STANDBY NOT ALLOWED
3.把主库切换为备库，重启后检查SWITCHOVER_STATUS为RECOVERY NEEDED:
ORA11GR2@SYS> alter database commit to switchover to physical standby with session shutdown; Database altered. ORA11GR2@SYS> shutdown abort
ORACLE instance shut down.
ORA11GR2@SYS> startup mount
ORACLE instance started. Total System Global Area 830930944 bytes
Fixed Size 2257800 bytes
Variable Size 570428536 bytes
Database Buffers 255852544 bytes
Redo Buffers 2392064 bytes
Database mounted.
ORA11GR2@SYS> select switchover_status from v$database; SWITCHOVER_STATUS
--------------------
RECOVERY NEEDED
4.转换完备库恢复日志后，SWITCHOVER_STATUS为TO PRIMARY：
ORA11GR2@SYS> recover managed standby database using current logfile disconnect from session;
Media recovery complete.
ORA11GR2@SYS> select switchover_status from v$database; SWITCHOVER_STATUS
--------------------
TO PRIMARY
5.查看备库的状态，并应用日志，只有当SWITCHOVER_STATUS是sessions active或者是to_primary状态时才可以切换角色：
SBDB@SYS> recover managed standby database using current logfile disconnect from session;
Media recovery complete.
SBDB@SYS> select switchover_status from v$database; SWITCHOVER_STATUS
--------------------
SESSIONS ACTIVE
6.切换备库并查看database_role，正常为primary：
SBDB@SYS> alter database commit to switchover to primary with session shutdown; Database altered. SBDB@SYS> alter database open; Database altered. SBDB@SYS> select database_role from v$database; DATABASE_ROLE
----------------
PRIMARY SBDB@SYS> select switchover_status from v$database; SWITCHOVER_STATUS
--------------------
RESOLVABLE GAP
7.转换后在备库（切换之前的主库）应用日志，并查看状态：
ORA11GR2@SYS> recover managed standby database using current logfile disconnect from session;
ORA-01153: an incompatible media recovery is active ORA11GR2@SYS> recover managed standby database cancel;
Media recovery complete.
ORA11GR2@SYS> select switchover_status from v$database; SWITCHOVER_STATUS
--------------------
NOT ALLOWED ORA11GR2@SYS> select database_role from v$database; DATABASE_ROLE
----------------
PHYSICAL STANDBY
8.再次查看转换后主库（切换之前的备库）的switchover_status，正常应为TO STANDBY：
SBDB@SYS> select switchover_status from v$database; SWITCHOVER_STATUS
--------------------
TO STANDBY