Forum Discussion

chetanhiwale's avatar
chetanhiwale
Resolver I
6 months ago
Solved

Issue with mirroring on-prem sql db with user defined datatypes.

Hi Folks, 

I am trying to mirror an onprem sql managed instance to Fabric. The sql  managed instance has some user defined datatypes. As Fabric docs says it doesnt supports user datatypes but when tested ( as of Jan 2026 ) , if the column is not a primary key column it works , else it throws an  error. 

Can someone confirm on this, if userdefined datatypes are supported or not ?
Docs ref : https://learn.microsoft.com/en-us/fabric/mirroring/azure-sql-managed-instance-limitations#column-level

Thanks 

Mirroring
Need Help
  • v-prasare's avatar
    v-prasare
    6 months ago

    Hi chetanhiwale,

    At this time, user-defined data types (UDTs) are not supported for Microsoft Fabric mirroring, as documented in the Azure SQL Managed Instance mirroring limitations. This limitation applies particularly to columns that participate in primary keys.

    Based on current product behavior:

    • Columns that use user-defined data types may mirror successfully when they are not part of a primary key.
    • If a primary key column is defined using a user-defined data type, the mirroring operation fails with an error.
    • This behavior is consistent with the documented limitation and should be considered unsupported, even if non–primary key columns appear to work in some scenarios.

    Recommendation

    To ensure reliable and supported mirroring to Microsoft Fabric:

    • Avoid using user-defined data types in primary key columns.
    • Use built-in SQL data types for all primary keys in databases that are mirrored to Fabric.

     

    Thanks,

    Prashanth

    MS Fabric community support

3 Replies

  • v-prasare's avatar
    v-prasare
    Community Support
    6 months ago

    Hi chetanhiwale,

    At this time, user-defined data types (UDTs) are not supported for Microsoft Fabric mirroring, as documented in the Azure SQL Managed Instance mirroring limitations. This limitation applies particularly to columns that participate in primary keys.

    Based on current product behavior:

    • Columns that use user-defined data types may mirror successfully when they are not part of a primary key.
    • If a primary key column is defined using a user-defined data type, the mirroring operation fails with an error.
    • This behavior is consistent with the documented limitation and should be considered unsupported, even if non–primary key columns appear to work in some scenarios.

    Recommendation

    To ensure reliable and supported mirroring to Microsoft Fabric:

    • Avoid using user-defined data types in primary key columns.
    • Use built-in SQL data types for all primary keys in databases that are mirrored to Fabric.

     

    Thanks,

    Prashanth

    MS Fabric community support

  • v-prasare's avatar
    v-prasare
    Community Support
    6 months ago

    Hi chetanhiwale,

    We would like to confirm if you've successfully resolved this issue or if you need further help. If you still have any questions or need more support, please feel free to let us know. We are more than happy to continue to help you.


    Thank you for your patience and look forward to hearing from you.
    Best Regards,

  • v-prasare's avatar
    v-prasare
    Community Support
    6 months ago

    Hi @chetanhiwale,

    We would like to confirm if you've successfully resolved this issue or if you need further help. If you still have any questions or need more support, please feel free to let us know. We are more than happy to continue to help you.


    Thanks

    Prashanth