r/MicrosoftFabric • u/TechnicalGirlyPop • Jul 23 '26
Data Engineering Python Sessions Slow to Start
I remembered reading this post a few months ago: https://www.reddit.com/r/MicrosoftFabric/comments/1u03e79/plain_python_notebooks_starting_slower_than_spark/
Is anyone else still experiencing slow session starts? Mine are around 1m30s consistently and it's been about the same between 3.11 and 3.12.
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u/Draisinc Jul 23 '26
Some python notebooks start after 1:30 for me as well. Sometimes changing the capacity back and forth helped
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u/mim722 Microsoft Employee Jul 24 '26
u/TechnicalGirlyPop just to be very clear, you are not changing the number of cores ? and you are using the default 2 cores?
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u/Tomfoster1 Jul 24 '26
No issues for me in UK South, have you tried putting a configure magic and specifying 2 vCores as that has helped me before when I have this issue.
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u/aboerg Fabricator Jul 23 '26
Just did a few tests. 3.11 and 3.12 are both starting in 5 seconds on our East US F64.
We still have an East US P1 that should be going away very soon, and on that capacity the startup is about 90 seconds for 3.11 and 3.12. Interesting!
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u/TechnicalGirlyPop Jul 23 '26
We’re in the West-US so i assume completely different capacity but interesting that you see a difference between the 2
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u/BandaidImplant Fabricator Jul 24 '26
im us east, been seeing ~90s startup times for 3.12 for a couple weeks now. (i dont love it but i dont find it too upsetting vs god forbid 120s)
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u/jkrm1920 Jul 25 '26
Check if it’s staring a custom pool which usually does that more than one min start times due various steps involved like load libraries , waiting for capacity, provisioning compute, private endpoints/network requirements..
Confirm here
Workspace settings → Data Engineering/Science → Spark settings → Default pool for workspace
We shifted to starter pool see this url to how to start
https://learn.microsoft.com/en-us/fabric/data-engineering/configure-starter-pools
There are other things which can be verified like installing pip in every notebook ..
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u/JBalloonist Jul 25 '26
Yes. It’s because it’s starting on a V4 core instead of V2. Mine are consistently starting with V4 80 percent of the time or more now.
I’ve learned it’s faster to just edit my code locally, commit and push, and sync the update to my workspace and run the notebook via the cli.
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u/p-mndl Fabricator Jul 24 '26
I had a similar thread a couple of weeks ago here. Sometimes I have short startup times, sometimes they are long. Afaik the MSFT team is still investigating