如何诊断job执行失败
1. 看job有没有机会执行
确保init.ora中job_queue_processes参数是否被设为>0的值.
show parameter job_queue_processes
2. 看是否执行job出错.
查看alert.log获取出错信息.
3. 看是否job所调用的procedure/package出错.
这个需要你自己在procedure/package中自己书写记录错误日志的代码.
4. 经常查看你的DBA_JOBS看看，相应的job是不是broken了，
BROKEN： Y: no attempt is made to run this job
N: an attempt is made to run this job
A job can be broken in two ways:
Oracle has failed to successfully execute the job after sixteen attempts. The job has been explicitly marked as broken by using the procedure DBMS_ JOB.BROKEN.
在尝试（默认）16次后还是不能成功执行，该job会被oracoracle账号le自动标记为broken=y
或者你可以手动运行看看，有什么错误提示。
EXECUTE DBMS_JOB.RUN(JOB_ID);