Some time ago a customer of mine (thank you, Robert Lochner) showed me a very interesting scenario where a set of Power Query queries in Power BI Desktop refreshed a lot faster with the “Enable Parallel Loading Of Tables” option turned off.
I have known for a long time that data privacy checks can have an impact on the performance of data refresh in Power BI and Excel, but on a recent performance tuning engagement I had the chance to observe just how much of a difference changing these settings can make
For a while now I’ve had an idea stuck in my head: wouldn’t it be cool to build a Power BI solution where a user could enter data into an Excel workbook and then, as soon as they had done so, they could see their new data in a Power BI report? It would be really useful for planning/budgeting applications and what-if analysis.
A lot of people have problems with the performance of OData data sources when loading data into Power BI and Excel. One possible cause of these problems is query folding not taking place – if this is the case then the Power Query engine will be requesting more data that is needed and applying any filters itself locally, rather than requesting filtered data from the data source. How do you know whether query folding is taking place or not though?
The use of parameter tables is a well-known technique in Power Query. It involves using a table from the current Excel workbook to hold various parameter values that are read using a Power Query query, and these parameter values are then passed to another Power Query query to control how it behaves. Ken Puls has a great post describing all this here, and similarly a lot of the demos in my video on on building a reporting solution in Power Query involve reading values from a table which are then used to filter data in a SQL query.