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Storing Constants For MDX Calculated Measures

Chris Webb walks us through an interesting performance problem when using Analysis Services multidimensional:

All it does is take the value of the Sales Amount measure at the lowest granularities of the Customer, Date and Product dimensions, multiply it by 0.08 to find a tax value, and because [Tax Amount] is a real, non-calculated measure, the result of the calculation aggregates up through the cube. [I know that I don’t have to aggregate the result of this specific calculation but remember that this is a simplified example – in the real case I did have to write the calculation using Scope statements – and anyway the best way of handling a basic multiplication like this would be with a measure expression]

The performance was sub-second for my test query and I was happy, but then I realised that the same tax rate was being used in other calculations and may change in the future, so I thought I would store the value 0.08 in a calculated measure:

Chris walks through several iterations of this before landing on a solution which is both reasonable and fast.