Here is why the size of small Power BI models is tens of MBs

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When creating our latest course “DAX for Power BI“, we scratched our heads about the size of our Power BI files. Even small data models took already tens of MBs. Here’s why:

If you are creating new Power BI reports, by default the “Auto Date/Time” function is turned on. This means that Power BI generates a date table for every single date field that it encounters in your model.

Power BI hides these automatic date tables for you, but exposes them via the column itself: if you click on a date column, automatically an entire date hierarchy will be displayed in your visual.

Magic Date Hierarchy in Power BI

Works great, right? Well, only if you really need it.

If you already have one or more Date Dimensions that you use inside your datamodel, chances are that you will hide the other key columns – so you don’t need those hidden tables.

If this is the case, then I urge you to disable the “Auto date/time” option for your data models – it turns out they grow your files quite a bit, especially in smaller models. In our case, the World Wide Importers dataset (we loaded only dimension stock item, dimension date and fact sales), the “auto date/time” tables grew our model from 5 to 31 MB – quite some impact on the size of Power BI files!

Of course – there are some functional reasons as well why you shouldn’t just go with the automatic date/time. See Alberto Ferrari’s article “Automatic Time Intelligence in Power BI” for example.

While we’re at it, maybe it’s time to take your Power BI skills to the next level – and really learn how to build data models using DAX?

Time to take the next step in your Power BI reports? Check out our new DAX course! (Or, if you’re just getting started, why not attend our one-day really-hands-on workshop “Dashboards and Reports using Power BI“?)

Training DAX voor Power BI


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