oracle 11g dataguard同步异常，PROTECTION_LEVEL为RESYNCHRONIZATION

起因：闪存区空间不足，导致DG出现异常。

恢复正常后，发现主、备库DG状态PROTECTION_LEVEL均为RESYNCHRONIZATION，

SQL> select protection_mode,protection_level from v$database;

PROTECTION_MODE      PROTECTION_LEVEL
-------------------- --------------------
MAXIMUM AVAILABILITY MAXIMUM RESYNCHRONIZATION

此时DG同步状态虽说设置为“MAXIMUM AVAILABILITY”，但实际上却非实时同步，而变为了异步同步了。

1、检查DG最高可用性（MAXIMUM AVAILABILITY）的

SQL> show parameter log_archive_dest_2

包含有lgwr sync affirm  ，是正确的。

2、检查alert日志，发现有如下提示：

RFS[6]: No standby redo logfiles available for thread 1
RFS[6]: No standby redo logfiles selected (reason:7)

发现备库缺少standby logfile。

数据库目录下 /data/oracle/app/oracle/oradata/orcl/ 下无 std_redo*.log 文件，而主库里有

3、查看备库redo 信息

SQL> select group#,type, member from v$logfile;

    GROUP# TYPE    MEMBER
---------- ------- -------------------------------------------------------
         3 ONLINE  /data/oracle/app/oracle/oradata/orcl/redo03.log
         2 ONLINE  /data/oracle/app/oracle/oradata/orcl/redo02.log
         1 ONLINE  /data/oracle/app/oracle/oradata/orcl/redo01.log
        11 STANDBY /data/oracle/app/oracle/oradata/orcl/std_redo11.log
        12 STANDBY /data/oracle/app/oracle/oradata/orcl/std_redo12.log
        13 STANDBY /data/oracle/app/oracle/oradata/orcl/std_redo13.log

4、删除备库redo的standby列表

SQL> alter database drop logfile group 11;
SQL> alter database drop logfile group 12; 
SQL> alter database drop logfile group 13;

5、暂时关闭取消Redo Apply（否则会报 ORA-01156: recovery or flashback in progress may need access to files错误）

SQL> alter database recover managed standby database cancel;

6、添加备用日志（standby redo ）

SQL> alter database add standby logfile group 11 ('/data/oracle/app/oracle/oradata/orcl/std_redo11.log') size 50M; 
SQL> alter database add standby logfile group 12 ('/data/oracle/app/oracle/oradata/orcl/std_redo12.log') size 50M; 
SQL> alter database add standby logfile group 13 ('/data/oracle/app/oracle/oradata/orcl/std_redo13.log') size 50M;

7、启用实时重做应用Redo Apply

SQL> alter database recover managed standby database using current logfile disconnect from session; 

现在再看看DG状态，已经恢复正常了。

SQL> select protection_mode,protection_level from v$database;

PROTECTION_MODE      PROTECTION_LEVEL
-------------------- --------------------
MAXIMUM AVAILABILITY MAXIMUM AVAILABILITY