What happens when query folding breaks?

< 1 min read

When query folding breaks, Power BI stops pushing transformations to the source.
After that step, all remaining processing happens locally in the Power BI engine.
This forces full data download instead of filtered extraction.
In my project, adding a custom column caused 10M rows to load fully.
Refresh time increased from 7 minutes to nearly 40 minutes.
Gateway memory usage also became very high and sometimes failed.
Network traffic increased because entire tables were transferred.
Database no longer handled joins or filters efficiently.
We fixed it by moving filters before the non-folding step.
So breaking folding directly impacts refresh performance and reliability.

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