Overview of Oracle Scheduler

To help you simplify the scheduling of hundreds or even thousands of tasks, Oracle Database includes Oracle Scheduler, an enterprise job scheduler. Oracle Scheduler (the Scheduler) is implemented by the procedures and functions in the DBMS_SCHEDULER PL/SQL package.

The Scheduler enables you to control when and where various computing tasks take place in the enterprise environment.The Scheduler helps you effectively manage and plan these tasks. By ensuring that many routine computing tasks occur without manual intervention, you can lower operating costs, implement more reliable routines, minimize human error, and shorten the time windows needed.

The Scheduler provides sophisticated, flexible enterprise scheduling functionality, which you can use to:

• Run database program units—PL/SQL anonymous blocks, PL/SQL stored procedures, and Java stored procedures—on the local database or on one or more remote Oracle databases.

• Run executables that are external to the database (external executables), such as applications, shell scripts, and batch files. You can run external executables on the local system or on one ore more remote systems. Remote systems do not require an Oracle Database installation; they require only a Scheduler agent. Scheduler agents are available for all platforms supported by Oracle Database and some additional platforms.

• Schedule job execution using the following methods:

  • Time-based scheduling

    You can schedule a job to run at a particular date and time, either once or on a repeating basis. You can define complex repeat intervals, such as "every Monday and Thursday at 3:00a.m except on public holidays" or "the last Wednesday of each business quarter." See "Creating, Running, and Managing Jobs" for more information.

  • Event-based scheduling

    The Scheduler enables you to start jobs in response to system or business events. Your applications can detect events and then signal the Scheduler. Depending on the type of signal sent, the Scheduler starts a specific job. Examples of event-based scheduling include starting jobs when a file arrives on a system, when inventory falls below predetermined levels, or when a transaction fails. Beginning with Oracle Database 11g Release 2, a Scheduler object called a file watcher simplifies the task of configuring a job to start when a file arrives on a local or remote system. See "Using Events to Start Jobs" for more information.

  • Dependency scheduling

    The Scheduler can run tasks based on the outcome of one or more previous tasks. You can define complex dependency chains that include branching and nested chains. See "Creating and Managing Job Chains" for more information.

• Prioritize jobs based on business requirements.

  The Scheduler enables control over resource allocation among competing jobs, thus aligning job processing with your business needs. This is accomplished in the following ways:

  • Jobs that share common characteristics and behavior can be grouped into larger entities called job classes. You can prioritize among the classes by controlling the resources allocated to each class. This enables you to ensure that your critical jobs have priority and have enough resources to complete. For example, if you have a critical project to load a data warehouse, then you can combine all the data warehousing jobs into one class and give priority to it over other jobs by allocating it a high percentage of the available resources. You can also assign relative priorities to the jobs within a job class.

  • The Scheduler takes prioritization of jobs one step further, by providing you the ability to change the prioritization based on a schedule. Because your definition of a critical job can change over time, the Scheduler enables you to also change the priority among your jobs over that time frame. For example, you may consider the extract, transfer, and load (ETL) jobs used to load a data warehouse to be critical jobs during non-peak hours but not during peak hours. However, jobs that must run during the close of a business quarter may need to take priority over the ETL jobs. In these cases, you can change the priority among the job classes by changing the resource allocated to each class. See "Creating Job Classes" and "Creating Windows" for more information.

• Manage and monitor jobs

  There are multiple states that a job undergoes from its creation to its completion. Scheduler activity is logged and information such as the status of the job and the last run time of the job can be easily tracked. This information is stored in views and can be easily queried using Enterprise Manager or SQL. These views provide valuable information about jobs and their execution that can help you schedule and better manage your jobs. For example, a DBA can easily track all jobs that failed for a particular user.

  When you create a multiple-destination job—a job that is defined at one database but that runs on multiple remote hosts—you can monitor the status of the job at each destination individually or the overall status of the parent job as a whole.

  For advanced job monitoring, your applications can subscribe to job state change notifications that the Scheduler delivers in event queues. The Scheduler can also send e-mail notifications when a job changes state.

  See "Monitoring and Managing the Scheduler".

• Execute and manage jobs in a clustered environment

  A cluster is a set of database instances that cooperates to perform the same task. Oracle Real Application Clusters (RAC) provides scalability and reliability without any change to your applications. The Scheduler fully supports execution of jobs in such a clustered environment. To balance the load on your system and for better performance, you can also specify the database service where you want a job to run. See "Using the Scheduler in Real Application Clusters Environments" for more information.