三言两语 - 关于JOB Queue的文档摘要

Job queue processes are used for batch processing. They run user
jobs. They can be viewed as a scheduler service that can be used to
schedule jobs as PL/SQL statements or procedures on an Oracle instance.
Given a start date and an interval, the job queue processes try to run
the job at the next occurrence of the interval.

Job queue processes are managed dynamically.Dynamic job queue processes can run a large number of jobs
concurrently at a given interval. The job queue processes run user jobs
as they are assigned by the CJQ process. Here's what happens:

1. 
   

   The coordinator process, named CJQ0, periodically selects jobs that
   need to be run from the system JOB$ table. New jobs
   selected are ordered by time.

   
   
2. 
   

   The CJQ0 process dynamically spawns job queue slave processes
   (J000...J999) to run the jobs.

   
   
3. 
   

   The job queue process runs one of the jobs that was selected by the
   CJQ process for execution. The processes run one job at a time.

   
   
4. 
   

   After the process finishes execution of a single job, it polls for
   more jobs. If no jobs are scheduled for execution, then it enters a
   sleep state, from which it wakes up at periodic intervals and polls for
   more jobs. If the process does not find any new jobs, then it aborts
   after a preset interval.

   
   

The initialization parameter JOB_QUEUE_PROCESSES
represents the maximum number of job queue processes that can
concurrently run on an instance. However, clients should not assume that
all job queue processes are available for job execution.

2.RAC环境中的JOB调度进程 （link）

Each RAC instance has its own job coordinator. The database monitoring
checks that determine whether or not to start the job coordinator do
take the service affinity of jobs into account. For example, if there is
only one job scheduled in the near future and the job class to which
this job belongs has service affinity for only two out of the four RAC
instances, only the job coordinators for those two instances will be
started.

3.JOB的实例调度 （link）

Because you can create jobs at the instance level, cluster level, or
cluster database level, jobs can run on any available host in the
cluster database.

You can administer Enterprise Manager jobs at both the
database and instance levels. For example, you can create a job at the
cluster database level and the job will run on any active instance of
the target Oracle RAC database. Or you can create a job at the instance
level and the job will only run on the specific instance for which you
created it. In the event of a failure, recurring jobs can run on a
surviving instance.