How Context Heuristics Works
The Context Heuristics switch injects the existing MDX function explicitly into the query as needed. The heuristic engine determines if the MDX function is needed in order to eliminate redundant query cycles. These redundant query cycles are sometimes produced in the Microsoft MDX engine when using two or more hierarchies from the SAME dimension on a specific axis (column or row).
By using the Context Heuristics switch, highly nested queries with sibling hierarchies can experience dramatic improvements in performance. In some rare cases the Context Heuristics switch can make queries slower – in which case the switch should be turned OFF.
Context Heuristics vs. NONEMPTY
The Context Heuristics switch should not be confused with the NONEMPTY function which removes sparsity from the cross join of hierarchies derived from DIFFERENT dimensions.
By default, the Context Heuristics switch is turned ON. This switch can be left ON at all times since BI Office is able to detect when it needs to be applied.
Open Query Options in Query Ribbon and select Context Heuristics.