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EBA38's avatar
EBA38
Regular Visitor
7 months ago
Solved

reload data after power query edit

Hi, I have a dataflow that pulls its data from Azure SQL, then feeds my semantic model, and finally my report. When I download the PBIX, it is 900 MB with the data. I open the PBIX in Power BI Desk...
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  • cengizhanarslan's avatar
    cengizhanarslan
    7 months ago

    Power BI Desktop is forced to fully re-materialize the table locally after any Power Query change, even if the data ultimately comes from a dataflow and even if you “just tweaked something small”.

     

    Best practice: Do NOT edit Power Query in the PBIX

    If the data comes from a dataflow:

    • Do all transformations in the dataflow
    • Keep the PBIX as thin as possible
    • Treat the PBIX as semantic + visuals only
Jaywant-Thorat's avatar
Jaywant-Thorat
Super User
7 months ago

This is a known but poorly explained Power BI behavior, and what you’re seeing is not a bug in your dataflow — it’s how Power BI Desktop handles large imported models.

What is REALLY happening - ROOT CAUSE

You have this chain:

Azure SQL → Dataflow → Semantic model → PBIX

When you:

  1. Download the PBIX (900 MB)

  2. Open it in Desktop

  3. Modify Power Query

  4. Click Close & Apply

Power BI Desktop does ALL of the following again:

Desktop does NOT reuse dataflow storage

  • It re-imports all data from the dataflow

  • It recompresses VertiPaq

  • It rebuilds dictionaries

  • It re-evaluates relationships

  • It recalculates calculated columns & tables

Even if you changed one small step, the entire model reloads

That’s why you see:

  • 300 MB… 600 MB… then stall

  • CPU + memory spike

  • No visible progress

  • Sometimes “finishes”, sometimes never

BEST PRACTICE: Do NOT transform in the report PBIX

Golden rule:
Never do heavy Power Query transformations in a report connected to large dataflows.

Correct architecture:

  • All transformations → Dataflow

  • PBIX → read-only import

  • Desktop only for:

    • Measures

    • Relationships

    • Visuals

If you need a change:

  1. Modify the dataflow

  2. Refresh dataflow in Service

  3. Open PBIX

  4. Refresh model (much faster)

This avoids re-materializing data locally.

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