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Windows 10, the most recent version of Power BI (but I had the problem earlier), 16GB RAM, Core i5 CPU, SSD. Everthing works great and really fast than suddenly it becomes drastically slow (in the same file with the same data and queries). The simplest query takes many minutes. I mean really the simplest, like removing duplicates from a table with one column and 2 identical records. It loads CPU at 100% for many minutes.
Backgrounds downloads disabled. Cleared cache. Reboted computer. Nothing helps. Copied the query into a new pbix file and it work as expected - I see the result of preview generating immediately, while it's still strugling in the main file. And it can be like this during many attempts and then just suddenly it works fast again (same file, same data, I didn't even closed the file, it was very slow, then suddenly it works fast). Had this problem with other reports in the past. Power Query works normally then with no visble reason it stucks on basic operations. No other heavy applications work in the background. Something is wrong with Power Query itself.
What it's doing? Some caching? It looks like a bug, probably I need to contact Microsoft, but maybe someone experienced this problem.
@avatorl
Do you have a very large query? This kind of problem is difficult to identify the exact reason. For some relevant suggestions, you could try to refer to Any way to speed up really slow refresh times in Power Query? | Power Query | Excel Forum for details.
Paul Zheng _ Community Support Team
If this post helps, please Accept it as the solution to help the other members find it more quickly.
This is how a basic power query preview loads the CPU:
Hi @avatorl,
there is a lot of parameters that may impact on the performance of the query. In your case, I would say, it is the step when you fetching data for the query if this is somewhere outside your hard drive, it can take some time and may vary quite a lot.
Kind regards,
JB
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