Many Scheduler capabilities enable database administrators to control more advanced aspects of scheduling. Typically, these topics are not as important for application developers.
This section discusses the following advanced topics:
A job class is a way of grouping jobs into larger entities, thus enabling you to prioritize access to the job slaves among those job classes. This means that you can, for example, make sure a CEO’s request will begin before a routine job. In addition to using job classes for resource allocation, you can also use them for setting job characteristics or behavior that must be the same for all the jobs in the class.
When defining job classes, you should try to classify jobs by functionality. Consider dividing jobs into groups that access similar data, such as marketing, production, sales, finance, and human resources.
Within a job class, you can:
Some of the restrictions to keep in mind are:
A window enables you to change resource allocation during a time period such as time of day or time of the sales year. You do this so you can control which groups of users have what level of priority. For example, you could control access to a printer so product managers have a lower priority than executives. A window is represented by an interval of time with a well-defined beginning and end, such as "from 12am-6am".
You can assign a priority with each window. If windows overlap, the window with the highest priority is chosen over other windows with lower priorities.
You use windows to guarantee that resources will be available when you need them. Therefore, you should try to avoid having more than one window active at the same time to minimize the potential for resources going to a less important task. It is not an error, however, for windows to overlap.
There are three windows so some rules need to be assigned for choosing which window will take precedence. The order of precedence for windows is as follows:
If at the end of a window there is still overlap with one or more windows, the Scheduler tries to switch to the window that has the highest priority and then, if the windows have the same priorities, to the one with the highest percentage of its duration remaining.
Overlapping windows are handled differently based on whether they have the same priority or not. When two or more windows of the same priority overlap, Oracle continues to run the window that was already running. After this window finishes running, Oracle switches to the one that still has the highest percentage of its duration left.
When high and low priority windows overlap, the Scheduler switches to the high priority window if it is currently running a low priority window. Jobs currently running that had a schedule naming the low priority window may be stopped depending on the behavior you assigned when you created the job. In addition, whenever two windows overlap, an entry is written in the Scheduler log.
You can group jobs for ease of use. An example would be to combine weekends, times from 12AM to 7AM, and holidays into something called "downtime". This downtime window group offers you more control over when jobs are run. In this case, perhaps the data warehousing department would only want their queries run during this time when they might be assigned a high percentage of available resources. A window group is only to combine windows and is only for jobs that use a window as a schedule.
Example of Window Group
A typical example of a window group is to have windows for weeknight, weekend, and holidays. A window group could be for combining them.
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Oracle 10g Tutorial
Overview Of Administering An Oracle Database
Creating An Oracle Database
Starting Up And Shutting Down
Managing Oracle Database Processes
Managing Control Files
Managing The Redo Log
Managing Archived Redo Logs
Managing Datafiles And Tempfiles
Managing The Undo Tablespace
Using Oracle-managed Files
Using Automatic Storage Management
Managing Space For Schema Objects
Managing Partitioned Tables And Indexes
Managing Hash Clusters
Managing Views, Sequences, And Synonyms
General Management Of Schema Objects
Detecting And Repairing Data Block Corruption
Managing Users And Securing The Database
Managing Automatic System Tasks Using The Maintenance Window
Using The Database Resource Manager
Moving From Dbms_job To Dbms_scheduler
Overview Of Scheduler Concepts
Using The Scheduler
Administering The Scheduler
Distributed Database Concepts
Managing A Distributed Database
Developing Applications For A Distributed Database System
Distributed Transactions Concepts
Managing Distributed Transactions
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