模式切换的完全的语法如下：

ALTER  DATABASE  SET  STANDBY  DATABASE  TO  MAXIMIZE  {PROTECTION  | AVAILABILITY |

PERFORMANCE}

１、最大保护转换为最大性能
SQL> alter database set standby database to maximize performance;
alter database set standby database to maximize performance
*
ERROR at line 1:
ORA-01126: database must be mounted EXCLUSIVE and not open for this operation

SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount;
ORACLE instance started.

Total System Global Area  236000356 bytes
Fixed Size                   451684 bytes
Variable Size             201326592 bytes
Database Buffers           33554432 bytes
Redo Buffers                 667648 bytes
Database mounted.
SQL> alter database set standby database to maximize performance;

Database altered.

SQL> alter database open;

Database altered.

SQL> select protection_mode,database_role from v$database;

PROTECTION_MODE
------------------------------------------------------------
DATABASE_ROLE
------------------------------------------------
MAXIMUM PERFORMANCE
PRIMARY
２、最大性能转换为最大可用

SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount;
ORACLE instance started.

Total System Global Area  236000356 bytes
Fixed Size                   451684 bytes
Variable Size             201326592 bytes
Database Buffers           33554432 bytes
Redo Buffers                 667648 bytes
Database mounted.
SQL> alter database set standby database to maximize availability;

Database altered.

SQL> alter database open;

Database altered.

SQL> select protection_mode,database_role from v$database;

PROTECTION_MODE
------------------------------------------------------------
DATABASE_ROLE
------------------------------------------------
MAXIMUM AVAILABILITY
PRIMARY

3、最大可用转换为最大保护
SQL> alter database set standby database to maximize protection;
alter database set standby database to maximize protection
*
ERROR at line 1:
ORA-01126: database must be mounted EXCLUSIVE and not open for this operation

SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount;
ORACLE instance started.

Total System Global Area  236000356 bytes
Fixed Size                   451684 bytes
Variable Size             201326592 bytes
Database Buffers           33554432 bytes
Redo Buffers                 667648 bytes
Database mounted.
SQL> alter database set standby database to maximize protection;

Database altered.

SQL> alter database open;

Database altered.

SQL>  select protection_mode,database_role from v$database;

PROTECTION_MODE
------------------------------------------------------------
DATABASE_ROLE
------------------------------------------------
MAXIMUM PROTECTION
PRIMARY