Microsoft Fabric 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 log entry is corrupted, malformed, or written by an incompatible Delta version. Reads and queries fail 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