Scheduler daemon

 

A scheduler daemon is a background thread that searches for tasks to run in the database.

A scheduler daemon is started for each scheduler defined on each server. If Scheduler 1 is configured on server1, then only one scheduler daemon runs on server1 unless it is cloned. If Scheduler 1 is defined at the node scope level, then the scheduler will run on each server within that node.

The poll interval determines the frequency at which the persistent store is queried. By default, this value is set to 30 seconds. When a task is found that is scheduled to run within the current poll interval, an asynchronous beans alarm is set. The task then runs as close to this time as possible using an alarm thread from the scheduler's associated work manager. Thus, the number of alarm threads configured on the work manager determines how many concurrent tasks are executed. No tasks are lost. If we reach this limit, then new tasks are simply queued to be executed when an alarm thread becomes available. The actual firing time is dictated by server load and availability of free threads in the alarm thread pool of the associated work manager.

 

Scheduler daemons in a cluster

When multiple schedulers are configured to use the same tables (as is the case in a clustered environment), any of the daemons can find a task and set the alarm in its Java virtual machine (JVM). The task is executed in the virtual machine where the scheduler daemon first runs, until the daemon is stopped and another daemon starts. If an application on server1 schedules a task to run and server2 was started before server1, then the task runs on server2.

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Sub-topics

Example: Stopping and starting scheduler daemons using Java Management Extensions API

Example: Dynamically changing scheduler daemon poll intervals using Java Management Extensions API

 

Related tasks

Configure schedulers
Developing and scheduling tasks

 

Related Reference

Schedulers collection
Interoperating with schedulers