data guard 的standby 点报错，Restarting dead background process QMN0。

SQL> show parameter aq;

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
aq_tm_processes                      integer     1
SQL> alter database recover managed standby database cancel;

Database altered.

SQL> alter system set aq_tm_processes=0 scope=both;

System altered.

SQL> shutdown immediate;
ORA-01109: database not open

Database dismounted.
ORACLE instance shut down.
SQL> startup nomount
ORACLE instance started.

Total System Global Area  455051936 bytes
Fixed Size                   731808 bytes
Variable Size             251658240 bytes
Database Buffers          201326592 bytes
Redo Buffers                1335296 bytes
SQL> alter database mount standby database;

Database altered.

SQL> show parameter aq;

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
aq_tm_processes                      integer     0
SQL> alter database recover managed standby database disconnect from session;

Database altered.

SQL> SELECT PROCESS, STATUS FROM V$MANAGED_STANDBY;

PROCESS   STATUS
--------- ------------
ARCH      CONNECTED
ARCH      CONNECTED
RFS       RECEIVING
MRP0      WAIT_FOR_LOG

SQL> select THREAD#,LOW_SEQUENCE#,HIGH_SEQUENCE# from v$archive_gap;

no rows selected

SQL> SELECT PROCESS, STATUS FROM V$MANAGED_STANDBY;

PROCESS   STATUS
--------- ------------
ARCH      CONNECTED
ARCH      CONNECTED
RFS       RECEIVING
MRP0      WAIT_FOR_LOG

SQL> select THREAD#,LOW_SEQUENCE#,HIGH_SEQUENCE# from v$archive_gap;

no rows selected

SQL> archive log list;
Database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            /home/oracle/productcr/dbs/arch
Oldest online log sequence     152841
Next log sequence to archive   0
Current log sequence           152850
SQL>

Queue Monitor Processes (QMNn)
队列监视进程是一个可选的后台进程，为Oracle Streams Advanced Queuing所使用。
最多可以配置10个队列监视进程。和Job进程一样，该进程的异常不会导致数据库的Crash。

通常这个错误不会导致数据库无法启动，但是在某些平台上会存在Bug,可能会导致数据库无法启动。
如果没有用到Oracle Streams Advanced Queuing选件，就可以取消该进程，数据库自然就可以启动了。