Base priority is the priority you assign to a task when you create it. The values are “high,” “medium,” and “low.” There is a run queue for each priority for each engine, and the global run queue also has a queue for each priority.
When an engine looks for a task to run, it first checks its own high-priority run queue, then the high-priority global run queue, then its own medium-priority run queue, and so on. The effect is that runnable tasks in the high-priority run queues are scheduled onto engines more quickly, than tasks in the other queues.
During execution, Adaptive Server can temporarily change a task’s priority if it needs to. It can be greater than or equal to, but never lower than, its base priority.
When you create a user-defined execution class, you can assign the values high, medium or low to the task.