MDX calculated measure slow when adding operations

Question

I have created a calculated measure through BIDS in a SSAS cube and it's like the following:

IIF([Measures].[RatePct] >= 0.90, [Measures].[measureA],  [Measures].[measureB])

The point is that if I convert the above to this:

IIF([Measures].[RatePct] >= 0.90, [Measures].[measureA],  0)

or that:

IIF([Measures].[RatePct] >= 0.90, [Measures].[measureA] + 100,  [Measures].[measureB])

the measure becomes extremely slow when using it in the cube.

Any ideas why this is happening and how can it be addressed?

Many thanks

Answer 1

That is because in both cases you are returning values that were earlier a possible null. Now the number of empty combinations have decreaded. Consider a case where [Measures].[measureA] was null but since you now have [Measures].[measureA] + 100 this will return 100 as a value. Now you UI will not be able to remove it as a null combination