In Delta lake maintenance, VACUUM removes old files no longer referenced by a Delta table log.

• A. Consolidates multiple Parquet files into a large file
• B. Removes old files no longer referenced by a Delta table log
• C. Applies optimized sorting, encoding, and compression to Delta parquet files to enable fast read operations
• D. Allows users to reference data without copying it

Answer: (B)

VACUUM is the maintenance action that reclaims storage by deleting data files that are no longer referenced by any active Delta table version. Delta Lake uses a transaction log to track which Parquet files belong to each version; when data is deleted or updated, some files become orphaned. After the retention window you configure passes, VACUUM removes those unreferenced files, freeing space while still preserving the ability to time-travel within the retention period.

It doesn’t perform file compaction or layout optimization (that’s what OPTIMIZE does), nor is it about referencing data without copying (that relates to data sharing or external access, not cleanup).