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 Oracle Scheduler Link Jobs with Job Classes
Oracle Tips by Burleson Consulting

Advanced Oracle Utilities: The Definitive Reference by Rampant TechPress is written by the top Oracle database experts (Bert Scalzo, Donald Burleson, and Steve Callan).  The following is an excerpt from the book.

The Oracle scheduler allows jobs to be linked with job classes, which in turn can be linked to services to allow jobs to run on specific nodes in a RAC environment.  To support the requirements for the job, two job classes might have to be created as follows:

  • These job classes can then be assigned to existing jobs or during job creation.

  • The use of services is not restricted to scheduled jobs.  These services can be used in the tnsnames.ora file to influence which nodes are used for each application.  An example of the tnsnames.ora file entries are displayed below.

  • As long as applications use the appropriate connection identifier, they should only connect to the nodes associated to the service.

Although not directly related to services, it is sensible to discuss the concept of instance stickiness at this point.  It has been shown that services can be used to associate jobs to one or more RAC instances in the cluster, but having a job run on a different instance each time can result in performance issues.  For example, a job on the first node of the cluster may be executed, during which time all the data necessary to perform the job is read from the disk into the buffer cache.  On the second execution, the job runs on the second node. 


As most of the data necessary to perform the job is already in the cache of the first node, the data must be passed across the clusters interconnect before the second job can proceed.  If the job had executed on the first node again, this network transfer would not have been necessary.  This is the reason for instance stickiness.


The instance_stickiness parameter for an individual job defaults to TRUE, meaning that the job will run repeatedly on the same node, assuming it is available and not severely overloaded.  The default value can be modified using the set_attribute procedure:


With the instance_stickiness parameter set to FALSE, the job can run on any available node in the cluster.


This chapter covered the fundamentals of job scheduling including both external schedulers like ones availables in Unix, Linux and Windows as well as Oracle’s internal scheduler. Various tools such as the crontab command, dbms_scheduler and dbms_jobs packages, and Scheduled Tasks Wizard in Windows were introducted with more emphasis put on the preferred scheduling method for scheduling jobs in Oracle, dbms_scheduler.


Another area of job scheduling that was covered concerned time-based scheduling. Such components as intervals, which is a way of storing a specific period of time that separates two datetime values, calendar syntax and Oracle job chains were explained in detail.  This chapter also showed how to identify and correct errors, how to email notifications of errors and how jobs can be monitored via using both database views and Oracle Enterprise Manager (OEM).


The chapter concluded with information regarding scheduler attributes, job priorities, scheduler logging, and details about the Job Resource Manager.

r more details on Oracle utilities, see the book "Advanced Oracle Utilities" by Bert Scalzo, Donald K. Burleson, and Steve Callan.

You can buy it direct from the publisher for 30% off directly from Rampant TechPress.


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