Over the past year or so I’ve been delivering a presentation on the Power Query engine’s data privacy settings at various conferences and Power BI user groups, in an attempt to try to pull together all the knowledge I have on this complex topic. Luckily, when I presented this session at the London Power BI User Group recently, they recorded it and posted it on YouTube here:
If you’re struggling with data privacy errors like:
Formula.Firewall: Query ‘Query1’ (step ‘xyz’) is accessing data sources that have privacy levels which cannot be used together. Please rebuild this data combination.
Formula.Firewall: Query ‘Query1’ (step ‘xyz’) references other queries or steps, so it may not directly access a data source. Please rebuild this data combination.
…in either the Power Query Editor in Power BI or Power Query/Get&Transform in Excel, then I hope this video will help you understand why you’re getting these errors and what you can do to avoid them.
A lot of what I show in this session draws on other material, such as:
- My five-part series of posts on the Power Query data privacy settings that starts here
- My post on how credentials and data privacy settings are stored for dynamic data sources here
- My post here on the performance overhead of applying data privacy checks
- Ehren von Lehe’s detailed paper on (available here) on how the engine partitions data sources while applying data privacy checks. One of the things I show in the video is that it’s now possible to see these partitions using Power Query Query Diagnostics (see here for some details – although I should probably devote a whole blog post to this in the future)
Lastly, one minor correction to something I said in the video: at the 44:32 mark I do a demo that shows how you can use M functions to avoid a Formula Firewall error. While this trick works in Power BI Desktop and Excel, it results in a dataset that can’t be refreshed in the Power BI Service unfortunately.