Avoid large parent-child dimensions that have 500,000 or members for the key attribute
This rule analyzes parent-child dimensions to determine whether they contain more than 500,000 members. Parent-child dimensions that contain more than 500,000 members are considered large.
Best Practices Recommendations
For best performance, you should typically eliminate the parent-child structure in large parent-child dimensions and materialize the levels into physical attributes. Large parent-child dimensions typically perform poorly because there are no aggregations on intermediate levels.
For More Information
For more information, see Defining a Parent-Child Hierarchy in SQL Server Books Online.