For this, you can create a table to insert the count value of running job in a particular time. then monitor few days or weeks , then decide what would be the correct value........
Parameter JOB_QUEUE_PROCESSES is maximum number of jobs that would ever be run concurrently on your Database.
1) First set JOB_QUEUE_PROCESSES higher than the most number of jobs that could ever run concurrently
2) Login as SYS
3) Create the table to do the monitoring
CREATE TABLE highest_concurrent_job (
4) Create the job to do the monitoring
CREATE OR REPLACE PROCEDURE DRP_highest_concurrent_job IS
INSERT INTO highest_concurrent_job
SELECT SYSDATE, COUNT(*) FROM DBA_JOBS_RUNNING;
5) Create the job queue job to do the monitoring
JOB => v_jobno,
WHAT => 'DRP_highest_concurrent_job;',
NEXT_DATE => SYSDATE,
INTERVAL => 'SYSDATE + (5/1440)');
6) select * from MAX_CONCURRENT_JOBS ;