---
type: concept
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  contentHash: 171ddaef904ba5428236cb88cb891834e7020026fb42323967a02d8602771d1b
  pageDirectory: concepts
  sources:
    - delta_alter_table_unset_managed_failed-error-condition-databricks-on-aws.md
  confidence: 1
  provenanceState: extracted
  freshnessStatus: unverified
  aliases:
    - delta_alter_table_unset_managed_failed
    - DELTA\_ALTER\_TABLE\_UNSET\_MANAGED\_FAILED
    - DELTA_ALTER_TABLE_UNSET_MANAGED_FAILED
    - delta_alter_table_unset_managed_failed-error-class
    - DEC
    - DELTA_ALTER_TABLE_UNSET_MANAGED_FAILED error class
  citations:
    - file: delta_alter_table_unset_managed_failed-error-condition-databricks-on-aws.md
title: DELTA_ALTER_TABLE_UNSET_MANAGED_FAILED
description: Databricks error class raised when a managed Delta table cannot be rolled back to an external table
tags:
  - databricks
  - error-message
  - delta-lake
timestamp: "2026-06-19T18:21:43.500Z"
---

---
title: DELTA_ALTER_TABLE_UNSET_MANAGED_FAILED
summary: Error condition raised when an ALTER TABLE UNSET MANAGED operation fails to roll back a managed Delta table to an external table.
sources:
  - delta_alter_table_unset_managed_failed-error-condition-databricks-on-aws.md
kind: concept
createdAt: "2026-06-19T23:26:29.432Z"
updatedAt: "2026-06-19T23:30:54.554Z"
tags:
  - error-message
  - databricks
  - delta-lake
  - unity-catalog
aliases:
  - delta_alter_table_unset_managed_failed
confidence: 1
provenanceState: extracted
inferredParagraphs: 0
---

# DELTA_ALTER_TABLE_UNSET_MANAGED_FAILED Error Condition

The **DELTA_ALTER_TABLE_UNSET_MANAGED_FAILED** error occurs when an attempt to roll back a [Managed table (Delta Lake)](/concepts/managed-tables-in-databricks.md) to an External table (Delta Lake) using `ALTER TABLE ... UNSET MANAGED` fails. This error ensures data integrity by preventing incomplete or unsafe conversions between table types. The error's associated SQLSTATE is `42809`, which falls under the class of syntax error or access rule violation. ^[delta_alter_table_unset_managed_failed-error-condition-databricks-on-aws.md]

The general error message is:

> `<table>` cannot be rolled back from managed to external table.

The error includes one of four sub‑conditions that describe the specific reason for the failure. ^[delta_alter_table_unset_managed_failed-error-condition-databricks-on-aws.md]

## Sub‑conditions

### TIME_WINDOW_EXCEEDED

The rollback operation must be performed within a limited time window after the table was originally migrated to a [Unity Catalog](/concepts/unity-catalog.md) managed table. If that window has passed, the rollback is no longer allowed. The error reports the number of days (`<numDays>`) within which rollback is supported. ^[delta_alter_table_unset_managed_failed-error-condition-databricks-on-aws.md]

### TRUNCATED_HISTORY

The table's [Delta Lake Transaction Log](/concepts/delta-lake-transaction-log.md) history has been truncated (e.g., by running `VACUUM` or `OPTIMIZE` with history retention settings). Rollback requires a complete set of commits to revert the table to its pre‑migration state; when those commits are missing, the operation fails. ^[delta_alter_table_unset_managed_failed-error-condition-databricks-on-aws.md]

### UNEXPECTED_ERROR

An unspecified internal error occurred during the rollback attempt. The error details are embedded in the message: ^[delta_alter_table_unset_managed_failed-error-condition-databricks-on-aws.md]

```
== Error ==
<error>
```

### VERSION_MISMATCH

The versions of the managed DeltaLog (`<managedDeltaLogVersion>`) and the external DeltaLog (`<externalDeltaLogVersion>`) do not match. This can happen if a concurrent `ALTER TABLE tbl UNSET MANAGED` command already successfully rolled back the table to an external table. In that case, the current operation sees a different table version than expected. ^[delta_alter_table_unset_managed_failed-error-condition-databricks-on-aws.md]

## Related Concepts

- [Managed table (Delta Lake)](/concepts/managed-tables-in-databricks.md) – A table whose data and metadata are fully managed by Delta Lake and Unity Catalog.
- External table (Delta Lake) – A table whose data resides in an external location, with only the metadata managed by Unity Catalog.
- [ALTER TABLE UNSET MANAGED](/concepts/alter-table-unset-managed-command.md) – The SQL command used to convert a managed table back to an external table.
- [Unity Catalog](/concepts/unity-catalog.md) – The [Metastore](/concepts/metastore.md) that governs table management and migration.
- [Delta Lake Transaction Log](/concepts/delta-lake-transaction-log.md) – The sequential log of all changes to a Delta table.

## Sources

- delta_alter_table_unset_managed_failed-error-condition-databricks-on-aws.md

# Citations

1. [delta_alter_table_unset_managed_failed-error-condition-databricks-on-aws.md](/references/delta_alter_table_unset_managed_failed-error-condition-databricks-on-aws-a24f2e75.md)
