Load Testing Tabular

I while back I did a TechEd presentation “Can Your BI Solution Scale?”, when I discussed a methodology for load testing SSAS and SSRS. A customer wanted to ensure that its Tabular model can scale to thousands of deployed users when it goes live.

You can still use the excellent Microsoft-originated AS Load Sim framework that I demonstrated in the presentation to load test Tabular. And you can use it can send both MDX and DAX queries.

One aspect that deserves more attention is how to tweak the framework to parameterize DAX queries. The framework was design to parameterize MDX queries with tupples. For example, if you want to parameterize an MDX query by month, you can specify the set NonEmpty( [Date].[Calendar].[Month].Members, [Measures].[Internet Sales Amount] ). Then, the framework executes the set and assigns tupples from the set in random so you don’t just get cached results from the same query.

However, you need to make a small change to the framework to parameterize DAX queries. Because DAX queries doesn’t support the MDX UniqueName syntax for filtering, you can’t parse the UniqueName of the tupple member to extract only the name. Instead, you can use the DAX MID function for this purpose. For example, if I want to filter the Customer[Customer Name] column on the actual name, e.g. Acme, you can use the following expression:

Customer[Customer Name] = MID(“([Customer].[Customer Name].&[Acme])”, SEARCH(“&[“, “([Customer].[Customer Name].&[Acme])”) + 2, SEARCH(“])”, “([Customer].[Customer Name].&[Acme])”) – SEARCH(“&[“, “([Customer].[Customer Name].&[Acme])”) – 2)

Basically, this expression extracts the string “Acme” from ([Customer].[Customer Name].&[Acme]). Since, the customer names will vary. it’s a generic and a rather convoluted expression to extract a string surrounded by “&[” and “])”.