What happens when a procedure executed by a JOB is not finished when is time for the JOB to execute it again?

Question

I want to know what happens when a procedure is executed through a job and before it finishes is time for the job to call the next execution of the procedure. Here the job I created:

DECLARE
  X NUMBER;
    BEGIN
      SYS.DBMS_JOB.SUBMIT
       (
          job        => x
         ,what       => 'BEGIN PKG_DISTRIBUIDOR_SCHEDULER.PRC_DISTRIBUYE_TRANSACCIONES(5000); END;'
         ,next_date  => to_date(sysdate,'dd/mm/yyyy hh24:mi:ss')
         ,interval   => 'SYSDATE+30/86400'
         ,no_parse   => FALSE
       );
       DBMS_OUTPUT.PUT_LINE('Job Number is: ' || to_char(x));   
       COMMIT;
   END;

As you can see, the job is executed each 30 seconds. So if my procedure (PRC_DISTRIBUYE_TRANSACCIONES) delays more than 30 seconds, what does the job do in this case?

Answer 1

If you use the (old deprecated) Jobs, i.e. DBMS_JOB

The starting time for the next execution is determined when the current jobs is finished. If you specify an interval as SYSDATE+30/86400 then it does not mean: "The job runs every 30 seconds."

It means: "The next jobs starts 30 seconds after the previous job has been finished."

If you use the Scheduler Jobs, i.e. DBMS_SCHEDULER

Immediately after a job starts, the repeat_interval (e.g. FREQ=SECONDLY;INTERVAL=30) 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. See About Setting the Repeat Interval

So it means: If a jobs last longer than 30 seconds then the new job will start immediately after the previous job has been finished.