DB2 Version 10.1 for Linux, UNIX, and Windows

Evaluation order of work classes in a work class set

A work class set can have multiple work classes that match with a database activity. To select which work class from a work class set an activity should fall under, the data server goes through the work classes according to the evaluation order, stopping at the first work class that matches the activity.

If no matching work class exists, the database activity does not belong to any work class, and no work action is applied to that activity.

You can affect the evaluation order of work classes in a work class set when you create or alter a work class set. When you create or alter a work class set, you determine the position at which a work class is placed in the work class set using one of the following three methods:

Specify the absolute position of the work class in the list.
For example, POSITION AT 2. In this situation, the work class is placed in the second position in the work class set, and the work class that was at the second position is now the third, the third work class is now the fourth, and so on. If the position specified for the work class by the CREATE WORK CLASS SET or ALTER WORK CLASS SET statement is greater than the total number of work classes in the work class set, the work class is positioned last in the list.
Use the POSITION BEFORE or POSITION AFTER keyword to specify the position of the work class relative to work classes already in the work class set.
Omit the position when creating a work class.
In this situation, the new work class is positioned at the end of the list. The position you specify for the work class in the work class set list is not necessarily the actual value of the EVALUATIONORDER column in the SYSCAT.WORKCLASSES view. The data server automatically assigns the order value to prevent gaps.

Work classes are processed in the order they are received, which can affect the evaluation order. For example, assume that you issue the following statement:

ALTER WORK CLASS SET WCS ALTER WORK CLASS C1 POSITION AT 1
   ALTER WORK CLASS C2 POSITION AT 1

As a result, the C1 work class has a evaluation order of 2 and the C2 work class has an evaluation order of 1 because C2 was the last work class processed.