What causes DELTA_ILLEGAL_STATE?

A concurrent write operation from an incompatible tool modified the Delta log outside of Delta Lake protocols. A Delta Lake library version mismatch between writers left the log in a partially upgraded state. The transaction log contains duplicate or out-of-order entries due to a storage system error. A manual edit or deletion of files in the _delta_log directory corrupted the log

How do I fix DELTA_ILLEGAL_STATE?

Step 1: Stop all writers to the affected table immediately to prevent further corruption.. Step 2: Run DESCRIBE HISTORY table_name to inspect recent operations and identify when the illegal state was introduced.. Step 3: Attempt RESTORE TABLE table_name TO VERSION AS OF N to roll back to a known-good checkpoint version.. Step 4: If restoration fails, contact Databricks support with the transaction log contents for forensic analysis.. Step 5: After recovery, ensure all writers use compatible Delta Lake library versions and no direct file system edits are made to _delta_log.

Critical severityexecution

Power BI Refresh Error:
DELTA_ILLEGAL_STATE

What does this error mean?

Delta Lake encountered an internal inconsistency in its own state, such as an invariant violation in the transaction log that should not be possible under normal operations.

Common causes

1A concurrent write operation from an incompatible tool modified the Delta log outside of Delta Lake protocols
2A Delta Lake library version mismatch between writers left the log in a partially upgraded state
3The transaction log contains duplicate or out-of-order entries due to a storage system error
4A manual edit or deletion of files in the _delta_log directory corrupted the log

How to fix it

1Step 1: Stop all writers to the affected table immediately to prevent further corruption.
2Step 2: Run DESCRIBE HISTORY table_name to inspect recent operations and identify when the illegal state was introduced.
3Step 3: Attempt RESTORE TABLE table_name TO VERSION AS OF N to roll back to a known-good checkpoint version.
4Step 4: If restoration fails, contact Databricks support with the transaction log contents for forensic analysis.
5Step 5: After recovery, ensure all writers use compatible Delta Lake library versions and no direct file system edits are made to _delta_log.

Frequently asked questions

Can VACUUM cause a DELTA_ILLEGAL_STATE error?

Unlikely if VACUUM is run through Delta Lake APIs. Running VACUUM with a retention period shorter than the default 7 days can break time travel but should not cause DELTA_ILLEGAL_STATE directly.

How do I prevent Delta log corruption?

Never directly edit files in the _delta_log directory, use compatible Delta Lake library versions across all writers, and enable optimistic concurrency control for concurrent writers.