JOB QUEUE PROCESSES parameter in 12C database

JOB QUEUE PROCESSES is used for background process in Oracle such as DBMS JOBS or scheduler job is running from this parameter.

If you set the value to zero then no scheduler or DBMS jobs is running in background. all jobs disabled to run.

Note:
Up to 12c, JOB_QUEUE_PROCESSES is set to a value in the range of 0 to 1000.
For 18c, JOB_QUEUE_PROCESSES is set to a value in the range of 0 to 4000.

Check the value of JOB QUEUE PROCESSES

[oracle@ora ~]$ sqlplus / as sysdba

SQL*Plus: Release 12.2.0.1.0 Production on Tue Jul 7 10:23:35 2020

Copyright (c) 1982, 2016, Oracle.  All rights reserved.

Connected to:
Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production

SQL>

SQL> Show parameter job_queue_processes

NAME                   TYPE     VALUE
---------------------- -------- -------
job_queue_processes    integer  4000

SQL> alter system set job_queue_processes=0;

System altered.

SQL> Show parameter job_queue_processes

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
job_queue_processes                  integer     0