7.5.5 Scheduler Component

Note

The scheduler component is included in MySQL Enterprise Edition, a commercial product. To learn more about commercial products, see https://www.mysql.com/products/.

The scheduler component provides an implementation of the mysql_scheduler service that enables applications, components, or plugins to configure, run, and unconfigure tasks every N seconds. For example, the audit_log server plugin calls the scheduler component at its initialization and configures a regular, recurring flush of its memory cache (see Enabling the Audit Log Flush Task).

• Purpose: Implements the component_scheduler.enabled system variable that controls whether the scheduler is actively executing tasks. At startup, the scheduler component registers the performance_schema.component_scheduler_tasks table, which lists the currently scheduled tasks and some runtime data about each one.

• URN: file://component_scheduler

For installation instructions, see Section 7.5.1, “Installing and Uninstalling Components”.

The scheduler component implements the service using these elements:

• A priority queue of the registered, inactive scheduled tasks sorted by the next time to run (in ascending order).

• A list of the registered, active tasks.

• A background thread that:

  • Sleeps if there are no tasks or if the top task needs more time to run. It wakes periodically to check whether it is time to end.

  • Compiles a list of the tasks that need to run, moves them from the inactive queue, adds them to the active queue, and executes each task individually.

  • After executing the task list, removes the tasks from the active list, adds them to the inactive list, and calculates the next time they need to run.

When a caller invokes the mysql_scheduler.create() service, it creates a new scheduled task instance to add to the queue, which signals the semaphore of the background thread. A handle to the new task is returned to the caller. The calling code should keep this handle and the service reference to the scheduling service until after calling the mysql_scheduler.destroy() service. When the caller invokes destroy() and passes in the handle it received from create(), the service waits for the task to become inactive (if running) and then removes it from the inactive queue.

The component service calls each application-provided callback (function pointer) into the same scheduler thread, one at a time and in ascending order, based on the time each requires to run.

Developers who wish to incorporate scheduler-queueing capabilities into an application, component, or plugin should consult the mysql_scheduler.h file in a MySQL source distribution.