Running VACUUM on a Databricks Delta table with 0 hours retention is strongly discouraged and potentially dangerous. Here’s why:

• Data Loss Risk: Vacuuming with 0-hour retention can delete active files that are still needed for ongoing transactions or queries. This can lead to inconsistent results, query failures, or even corruption of the Delta table.

• Safety Check: Databricks has a built-in safety check to prevent you from running such a risky command. By default, it won’t allow you to vacuum with a retention period less than 7 days.

Alternatives and Recommendations:

• Use the Default Retention (7 days): The default retention period is generally safe and sufficient for most use cases. It ensures that files are only deleted after they are no longer needed for time travel or concurrent operations.

• Increase Retention for Longer Time Travel: If you need to retain older versions of your data for longer periods, you can explicitly set the retention period to a higher value (e.g., 30 days, 90 days).

• Dry Run: If you’re unsure about which files will be deleted, you can use the DRY RUN option with the VACUUM command. This will list the files that would be deleted without actually removing them.

Example (Dry Run):

VACUUM yourDeltaTable DRY RUN RETAIN 0 HOURS

Important Note: Even with a dry run, be extremely cautious when using 0-hour retention. Only proceed if you are absolutely certain that there are no active transactions or queries that might depend on the files that would be deleted.