JOB_QUEUE_PROCESSES specifies the maximum number of job slaves per instance that can be created for the execution of DBMS_JOB jobs and Oracle Scheduler (DBMS_SCHEDULER) jobs. DBMS_JOB and Oracle Scheduler share the same job coordinator and job slaves, and they are both controlled by the JOB_QUEUE_PROCESSES parameter.

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   If the value of JOB_QUEUE_PROCESSES is set to 0, then DBMS_JOB jobs and Oracle Scheduler jobs will not run on the instance.If JOB_QUEUE_PROCESSES is set to a value in the range of 1 to 1000, then DBMS_JOB jobs and Oracle Scheduler jobs will run. The actual number of job slaves created for Oracle Scheduler jobs is auto-tuned by the Scheduler depending on several factors, including available resources, Resource Manager settings, and currently running jobs. However, the combined total number of job slaves running DBMS_JOB jobs and Oracle Scheduler jobs on an instance can never exceed the value of JOB_QUEUE_PROCESSES for that instance. The number of job slaves running Oracle Scheduler jobs is additionally limited to the value of the MAX_JOB_SLAVE_PROCESSES Scheduler attribute.

   Advanced replication uses Oracle Scheduler for data refreshes. Oracle Streams Advanced Queuing uses Oracle Scheduler for message propagation. Materialized views use Oracle Scheduler for automatic refreshes. Setting JOB_QUEUE_PROCESS to 0 will disable these features as well as any other features that use Oracle Scheduler or DBMS_JOB.

a、對(duì)于Oracle job進(jìn)程，包含協(xié)調(diào)進(jìn)程(主進(jìn)程)以及奴隸進(jìn)程(子進(jìn)程)。
b、job_queue_processes取值范圍為0到1000，總共可創(chuàng)建多少個(gè)job進(jìn)程由job_queue_processes參數(shù)來(lái)決定。
c、當(dāng)job_queue_processes大于1時(shí)，且并行執(zhí)行job時(shí)，至少一個(gè)為協(xié)調(diào)進(jìn)程。其總數(shù)不會(huì)超出job_queue_processes的值。
d、job_queue_processes參數(shù)的值為且DBMS_JOB與DBMS_SCHEDULER共享。
e、job_queue_processes參數(shù)，當(dāng)設(shè)定該值為0的時(shí)候則任意方式創(chuàng)建的job都不會(huì)運(yùn)行。
f、非零值的job_queue_processes，其job子進(jìn)程數(shù)依賴(lài)于可用資源，資源配置方式以及當(dāng)前運(yùn)行的job數(shù)來(lái)自行調(diào)整。
g、此外對(duì)于Scheduler jobs方式還受限制于scheduler屬性MAX_JOB_SLAVE_PROCESSES的設(shè)置。
h、可以通過(guò)DBMS_SCHEDULER.SET_SCHEDULER_ATTRIBUTE來(lái)設(shè)置max_job_slave_processes

此參數(shù)可以alter system立即生效