【测试】DG的主切备，备切主

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