Execution class attributes

Each predefined or user-defined execution class is composed of a combination of three attributes: base priority, time slice, and an engine affinity. These attributes determine performance characteristics during execution.

The attributes for the predefined execution classes, EC1, EC2, and EC3, are fixed, as shown in Table 4-1. You specify the mix of attribute values for user-defined execution classes when you create them, using sp_addexeclass.

**Table 4-1: Fixed-attribute composition of predefined execution classes**
Execution class level	Base priority attribute*	Time slice attribute **	Engine affinity attribute***
EC1	High	Time slice > t	None
EC2	Medium	Time slice = t	None
EC3	Low	Time slice < t	Engine with the highest engine ID number

See “Base priority”, “Time slice” and “Task-to-engine affinity” for more information.

By default, a task on Adaptive Server operates with the same attributes as EC2: its base priority is medium, its time slice is set to one tick, and it can run on any engine.