What causes Delta Schema Deserialization Error?

Interrupting a notebook mid-write leaves the transaction log in a partially written state. Schema evolution wrote a schema format that a lower Delta version cannot parse (version mismatch between writer and reader). Manual edits or deletions of files inside the _delta_log directory. Storage-level corruption of the last Delta log file (e.g., due to a failed upload)

How do I fix Delta Schema Deserialization Error?

Try reading the table with a RESTORE TABLE command to roll back to a known-good version: RESTORE TABLE TO VERSION AS OF . Check the _delta_log directory for the most recent .json checkpoint file and verify it is complete and valid JSON. Run DESCRIBE HISTORY to find the last successful schema version before the corruption. If RESTORE is not possible, recreate the Delta table from the underlying Parquet files using delta.io conversion: CONVERT TO DELTA parquet.

High severityfabric

Power BI Refresh Error:
Delta Schema Deserialization Error

What does this error mean?

Delta Lake cannot parse the schema stored in the transaction log for a Fabric Lakehouse table. The transaction log entry is corrupted, malformed, or was written by an incompatible Delta version. This prevents reads and queries against the affected table until the metadata is repaired.

Common causes

1Interrupting a notebook mid-write leaves the transaction log in a partially written state
2Schema evolution wrote a schema format that a lower Delta version cannot parse (version mismatch between writer and reader)
3Manual edits or deletions of files inside the _delta_log directory
4Storage-level corruption of the last Delta log file (e.g., due to a failed upload)

How to fix it

1Try reading the table with a RESTORE TABLE command to roll back to a known-good version: RESTORE TABLE <table> TO VERSION AS OF <version>
2Check the _delta_log directory for the most recent .json checkpoint file and verify it is complete and valid JSON
3Run DESCRIBE HISTORY <table> to find the last successful schema version before the corruption
4If RESTORE is not possible, recreate the Delta table from the underlying Parquet files using delta.io conversion: CONVERT TO DELTA parquet.<path>

Beyond the docs

Common practitioner solutions not covered in the official documentation.

1Ensure notebooks writing to the table complete without interruption — avoid killing Spark sessions mid-write

Official documentation: https://learn.microsoft.com/en-us/fabric/data-engineering/troubleshoot-lakehouse