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Lanceometer's avatar
Lanceometer
Icon for Helper I rankHelper I
3 months ago
Solved

Mirrored Snowflake Database Storage

Hi Folks,   Some info upfront: - We use a Fabric F16 Capacity - I know the F16 Capacity offers 16TB free mirroring Storage   I was trying the Mirrored Snowflake Database. It worked well. It was...
capacities
governance
one lake
  • Dev_Dholakia's avatar
    Dev_Dholakia
    3 months ago

    Hey Lanceometer ,

     

    You have diagnosed it right, this is a source-side pattern, not a Fabric bug.

    • Why storage grows: Fabric mirroring uses Snowflake Streams (CDC). A nightly full rebuild makes every row look new, so a fresh set of Parquet files gets written each cycle while older Delta versions stick around
    • 1 day retention: It's only a threshold for when old files become eligible for cleanup, not  guarantee that vacuum runs daily
    • Manual VACUUM: Not supported on a mirrored database. Maintenance is handled internally (OPTIMIZE runs roughly every ~50 writes per table)

    Next steps:

    • Real fix: ask the Snowflake team to switch to incremental MERGE/UPDATE instead of a nightly rebuild
    • Otherwise, skip mirroring for this table — use a OneLake shortcut or a pipeline load
    • Keep retention at 1 day and give it a couple of cycles to plateau

    Useful links:

    Mirroring Snowflake in Fabric
    VACUUM Delta tables

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suparnababu8's avatar
suparnababu8
Icon for Super User rankSuper User
3 months ago

Hello Lanceometer 

 

Yes, your asumption is correct. Fabric keeps old recods as backup. to answer your question, you can vacumm the old files daily but it does not automatically delete the files. So, Delat tables required explicit vacumme. you can clean up them manullay. Pls read this thread https://learn.microsoft.com/en-us/fabric/data-engineering/delta-lake-vacuum?tabs=sparksql it might helps you.

 

Thank you!!

 

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