， 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
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount;
ORACLE instance started.
Total System Global Area 167772160 bytes
Fixed Size 1218316 bytes
Variable Size 79694068 bytes
Database Buffers 83886080 bytes
Redo Buffers 2973696 bytes
Database mounted.
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=dg_st lgwr sync AFFIRM';
System altered.
SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount;
ORACLE instance started.
Total System Global Area 167772160 bytes
Fixed Size 1218316 bytes
Variable Size 79694068 bytes
Database Buffers 83886080 bytes
Redo Buffers 2973696 bytes
Database mounted.
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$database;
PROTECTION_MODE PROTECTION_LEVEL
-------------------- --------------------
MAXIMUM AVAILABILITY MAXIMUM AVAILABILITY
alter database set standby database to maximize performance;
提示：maximize后可跟{PROTECTION | AVAILABILITY | PERFORMANCE}，分别对应最大保护，最高可用性及最高性能。
在最大保护模式下，直接关闭备库是不行的，如果在备库上关闭
数据库，会有如下提示：
SQL> shutdown immediate
ORA-01154: database busy. Open, close, mount, and dismount not allowed now
SQL>
在最大保护模式下，备库是不允许关闭的，此时首先关闭主库，然后备库就可以顺利关闭了
注意： 主库的保护模式修改之后，备库的模式也会改变，和主库保持一致。
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3. 查看日志归档情况
主库进行日志切换:
SQL>Alter system switch logfile;
select max(sequence#) from v$archived_log;
select max(sequence#) from v$log_history;
select group#,sequence#,archived,status from v$log;
select name,sequence#,applied from v$archived_log;
select sequence#,applied from v$archived_log;
若不同步，
1>看log日志， archive是否有丢失
2>可以在备库坐如下操作：
--停止redo apply
alter database recover managed standby database cancel;
--开始redo apply
alter database recover managed standby database disconnect from session;