How to improve subform performance

For example, to link to the subform on an Employee ID field and an Order ID field, add a text box to the main form with the following properties:
Name: EmployeeIDOrderID
ControlSource: =[EmployeeID] & [OrderID]

Next, add the following field to the query that the subform is based on:
EmployeeIDOrderID: [Employee ID] & [Order ID]

Finally, link the main form and the subform on the concatenated field rather than on the two individual fields. The subform properties may appear as follows:
LinkChildFields: EmployeeIDOrderID
LinkMasterFields: EmployeeIDOrderID

Because Microsoft Access has to compare only one criteria to return the subform's recordset, the subform's performance should improve.