Jobs timings has changed in oracle 9i

Question

In our database we are having 3 jobs scheduled using dbms_jobs, but every 3 or 4 days once these jobs timing are changing,can any body help me out why this is being happening.
i scheduled the jobs using below script
DECLARE
X NUMBER;
BEGIN
SYS.DBMS_JOB.SUBMIT
( job => X
,what => 'GPS_DATA;'
,next_date => TO_DATE('23/10/2008 06:30:00','dd/mm/yyyy hh24:mi:ss')
,INTERVAL => 'sysdate+1'
,no_parse => TRUE
END;
like this i scheduled and it should execute every day at 6:30AM, but every few days the next and last timing are showing 9:20AM some times another timing..
and i checked once that when the database is bounced then all the jobs are started at database startup time..i dont know y this is happening
help me out to solve this one...
thanks a lot
.

Answer 1

If a job is scheduled to run at 06:30am and the INTERVAL is 'sysdate+1'
AND
the database is shutdown between 06:00 and 09:00 on Monday morning
At startup (at 09:00), Oracle finds that a job that was supposed to have run at 06:30 hasn't run yet. It begins running the job now -- ie 09:00 or 09:01.
When the job finished, the INTERVAL being 'sysdate+1' sets the Next schedule time to be 09:00 of Tuesday morning !!
It is behaving as expected and designed !
If you are on 10g, you can move to using dbms_scheduler.
If you are still using dbms_job, you'd have to modify the INTERVAL specification such that it always starts from a specific time --- eg 'trunc(sysdate) + 13/24' will always be the 6:30am of tomorrow irrespective of whether the current sysdate is 06:30am or 09:00am !
However, as for the first run of the job after startup at 09:00 -- you could build some additional scripting to disable jobs from running at this time or reschedule them or allow them to run -- depending on whether you can afford to not have the 06:30am run of Monday at all or whether it is very important to run, even if at 09:00 !
Hemant K Chitale
http://hemantoracledba.blogspot.com