About DBMS_JOB

DBMS_JOB is a PL/SQL package that you use to schedule jobs. It is replaced by Oracle Scheduler, which is more powerful and flexible. Although Oracle recommends that you switch from DBMS_JOB to Oracle Scheduler, DBMS_JOB is still supported for backward compatibility.

Configuring DBMS_JOB

The JOB_QUEUE_PROCESSES initialization parameter specifies the maximum number of processes that can be created for the execution of jobs. Beginning with Oracle Database release 11g, JOB_QUEUE_PROCESSES defaults to 1000. The job coordinator process starts only as many job queue processes as are required, based on the number of jobs to run and available resources. You can set JOB_QUEUE_PROCESSES to a lower number to limit the number of job queue processes. Setting JOB_QUEUE_PROCESSES to 0 disables DBMS_JOB.

Using Both DBMS_JOB and Oracle Scheduler

DBMS_JOB and Oracle Scheduler (the Scheduler) use the same job coordinator to start job queue processes. (For the Scheduler, these processes are called job slave processes. This section uses these terms interchangeably.) Although you typically use the JOB_QUEUE_PROCESSES initialization parameter to limit the number job queue processes for DBMS_JOB and you use the Scheduler attribute max_job_slave_processes to limit the number of job slave processes for the Scheduler, the Scheduler is affected by the JOB_QUEUE_PROCESSES parameter.

The maximum number of job slave processes for Scheduler is determined by the lesser of the values of JOB_QUEUE_PROCESSES and max_job_slave_processes. For example:

If JOB_QUEUE_PROCESSES is set to 10 and max_job_slave_processes is set to 20, the job coordinator will start no more than 10 job slave processes to be shared between DBMS_JOB and the Scheduler.
If JOB_QUEUE_PROCESSES is 20 and max_job_slave_processes is 10, the coordinator will start up to 20 job slave processes. The Scheduler can use only 10 of these, but DBMS_JOB can use all 20.

If JOB_QUEUE_PROCESSES is 0, DBMS_JOB is disabled, and the maximum number of job slave processes for Scheduler is controlled by the max_job_slave_processes Scheduler attribute.