Debugging SSAS Cubes – a Few Tips

There are a few techniques which can contribute to this topic and I will list some tips which seem to elude many people experiencing problems with their implementations.

1. Do not use the Cube Browser and Excel for troubleshooting

Yes, it is convenient to just drag-drop some hierarchies and measures in the Cube Browser, or in Excel, but when you have troubles with your results these tools will obscure the results. This is happening because every client tool has to generate MDX and by doing so they often generalise the approach and add “nice” language constructs like VisualTotals, or always use a subselect clause. There is nothing wrong with checking the end-result of your work with tools showing what your users see, but when your calcs don’t behave the way you expect (especially when filtering things), I would definitely stay away from GUI clients. Instead you can write some MDX in SSMS and pull exactly what you need in a clean and straight-forward way. We can play with swapping WHERE clauses for subselects, add calculations directly in the queries, etc – in brief, we get the full calculation power of MDX in our hands for troubleshooting. Additionally, next time you ask a question someone else you can start with “I have this MDX query…” instead of: “I have this pivot grid in Product X…” – it is much more likely that you will get a meaningful response.

2. Use SQL Server Profiler

If your MDX works perfectly fine against your cube, but when you use Excel 20xx you get funny results, there is no better way to find what the problem is than to run a trace with SQL Server Profiler, capture the MDX the tool has generated and then work with that to debug – again in SSMS. Different versions of Excel generate different MDX and the difference can be very important. When using other tools the differences become even larger. The only way to see what your tools does (other than talk to the people who have built it) is to capture its SSAS queries.

3. Ask for help

Once you have arrived at the conclusion that you need help (e.g. after exhaustively searching for the problem online), you can quickly get an answer at a few forums. My preferred one is MDSN, which has a dedicated SSAS section. Also, you can ask at the www.ssas-info.com forum section, or even at StackOverflow. Either way, you will need to know what the versions of each product you are using are (especially SQL Server version, service packs and updates applied) and ideally – post your MDX (if you have 10 pages of queries it would help to somehow abbreviate the repeating sections instead of copy-pasting the lot). Do not also forget that the people who are reading your questions do not know your dimensional model and what features of SSAS you are using (e.g. LastNonEmpty, unary operators, etc.) – make sure that you describe any specifics – otherwise everyone would assume a typical star with a straight-forward implementation in SSAS. These approaches, together with being courteous and good with spelling and grammar, will help attract fellow developers, who may know a little SSAS quirk, or MDX feature which resolves your issue.

4. Use Adventure Works

Replicating you problems in Adventure Works is another great way to ensure you get an accurate answer. Because typically everyone on the forums has access to Adventure Works, showing some MDX which results in an unexpected for you outcomes is the best way to pinpoint the problem eliminating all question marks which your specific model and data could be introducing. Additionally, you will probably get an answer which includes some sample code and you will be able to run it immediately and see the results.