How can I ensure that a dbms_scheduler job will never have more than one instance running?

For example, if I have a job that is scheduled to run once a minute, but it actually runs for three minutes, I don't want a second and third instance of the job to start and run concurrently.

(note) I previously asked this question specifying that either dbms_scheduler or dbms_jobs solutions were acceptable. I have since learned that dbms_jobs does not work well on RAC, hence this dbms_scheduler-specific question. (end note)

  • Can you schedule the job using a bash script?
    – Vérace
    Aug 12, 2015 at 7:27
  • Query dba_scheduler_jobs_running to see if the job is already running, and exit if it is Oct 10, 2016 at 13:16

2 Answers 2


yes, you can, this in fact is default behaviour. See Database Administrator’s Guide chapter 29 Scheduling Jobs with Oracle Scheduler

Immediately after a job starts, the repeat_interval is evaluated to determine the next scheduled execution time of the job. While this might arrive while the job is still running, a new instance of the job does not start until the current one completes.


Doesn't this accomplish the same thing that @Justin Cave did in the other thread?

   job_name             => 'hr.employees_jobs',
   job_type             => 'PLSQL_BLOCK',
   job_action           => 'BEGIN proc_that_takes_3_minutes; END;',
   start_date           => systimestamp,  
   repeat_interval      => 'FREQ=MINUTELY;INTERVAL=1',
   enabled              =>  TRUE,
   comments             => 'Gather table stats on hr.employees'
) ;
  • 2
    by my understanding, dbms_job reschedules at the end of each job run, whereas dbms_scheduler starts at the scheduled time even if another job is running. Aug 12, 2015 at 22:55

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