Oracle对于这个错误的描述为：

ORA-31623: a job is not attached to this session via the specified handle
Cause: An attempt to reference a job using a handle which is invalid or no longer valid for the current session.
Action: Select a handle corresponding to a valid active job or start a new job.

从这个错误看不出导致问题的真正原因，不过从告警日志中可以发现进一步的信息：

Tue Jan 17 19:30:08 2012
Errors in file /opt/oracle/diag/rdbms/mobiledb_n/mobiledb/trace/mobiledb_ora_17167.trc (incident=84810):
ORA-04031: unable to allocate 56 bytes of shared memory ("streams pool","unknown object","streams pool","fixed allocation callback")
Incident details in: /opt/oracle/diag/rdbms/mobiledb_n/mobiledb/incident/incdir_84810/mobiledb_ora_17167_i84810.trc
Use ADRCI or Support Workbench to package the incident.
See Note 411.1 at My Oracle Support for error and packaging details.
Tue Jan 17 19:30:11 2012
Dumping diagnostic data in directory=[cdmp_20120117193011], requested by (instance=1, sid=17167), summary=[incident=84810].
Tue Jan 17 19:30:12 2012
Sweep [inc][84810]: completed
Sweep [inc2][84810]: completed

数据库在尝试分配STREAMS POOL的时候出现了ORA-4031错误。此时查询V$MEMORY_RESIZE_OPS视图，发现同一时间大量的STREAMS POOL扩展失败的记录，Oracle尝试分配STREAMS POOL但是目前数据库的内存采用了在SGA_TARGET下手工分配的方式，为了避免Oracle内存的动态调整，所有的内存组件已经将内存全部使用，因此STREAMS POOL无法获取到空间。

解决问题的方法很简单，手工收缩DB_CACHE_SIZE或SHARED_POOL_SIZE的值，分配给STREAMS POOL，就可以避免这个错误，不过数据泵的导出还要使用STREAMS POOL，还是第一次发现这个问题。