保护模式切换
Maximum protection/availability/ performance
1. 首先查看当前的保护模式
SQL> select protection_mode,protection_level from v$database;
PROTECTION_MODE PROTECTION_LEVEL
-------------------- --------------------
MAXIMUM PERFORMANCE MAXIMUM PERFORMANCE
2. 设置新的数据保护模式并重启数据库 --primary数据库操作
当满足如下条件Maximum protection/AVAILABILITY/ performance 可以自由切换
Redo Archival Process: LGWR
Network Tranmission mode: SYNC
Disk Write Option: AFFIRM
Standby Redo Logs: Yes
standby database type: Physical Only
alter database set standby database to maximize protection;
alter database set standby database to maximize availability;
alter database set standby database to maximize performance;
在最大保护模式下，直接关闭备库是不行的，如果在备库上关闭数据库，会有如下提示：
SQL> shutdown immediate
ORA-01154: database busy. Open, close, mount, and dismount not allowed now
SQL>
在最大保护模式下，备库是不允许关闭的，此时首先关闭主库，然后备库就可以顺利关闭了。
注意： 主库的保护模式修改之后，备库的模式也会改变，和主库保持一致。
当保护模式更改顺序：
maximize protection --->maximize availability --->maximize performance
当在把dataguard的保护级别按这上面的顺序减低的时候，不需要primary库在mount状态，否则primary 必须在mount 状态。
如：
SQL> alter database set standby database to maximize availability;
alter database set standby database to maximize availability
*
ERROR at line 1:
ORA-01126: database must be mounted in this instance and not open in any instance
SQL> shutdown immediate
SQL> startup mount;
SQL> alter database set standby database to maximize availability;
Database altered.
SQL> alter database open;
alter database open
*
ERROR at line 1:
ORA-03113: end-of-file on communication channel
报错了，这是因为最大可用性需要先修改日志传送方式为lgwr同步方式，否则，数据库是无法open.
SQL> alter system set log_archive_dest_2='service=orcl_st lgwr sync AFFIRM';
System altered.
SQL> shutdown immediate
SQL> startup mount;
SQL> alter database set standby database to maximize availability;
Database altered.
SQL> alter database open;
Database altered.
SQL> select protection_mode,protection_level from v$database;
PROTECTION_MODE PROTECTION_LEVEL
-------------------- --------------------
MAXIMUM AVAILABILITY MAXIMUM AVAILABILITY