After repeatedly running OPTIMIZE on a Lakehouse Delta table, an engineer notices the table's storage footprint has grown because the old pre-compaction files are still present alongside the new compacted ones. Compliance requires the ability to time travel back seven days, but anything older than that can be discarded to reclaim space. Which action removes the obsolete data files while preserving the required seven-day history?
- ARun OPTIMIZE again, which will overwrite the obsolete files in place and free the space they occupied while keeping the seven-day history intact.
- BDisable V-Order on the table, which signals Fabric to discard the redundant unreferenced files created by previous optimised writes.
- CRun VACUUM with a retention of seven days, which physically deletes data files unreferenced and older than that window while keeping recent history. Correct
- DLower the Delta log retention property alone, after which the obsolete data files are automatically deleted once they pass the new threshold.
Why A is wrong: OPTIMIZE rewrites data into new files and marks old ones as unreferenced rather than deleting them, so running it again adds more files and increases storage instead of reclaiming it.
Why B is wrong: V-Order controls write-time data layout and has no role in deleting unreferenced files, so toggling it neither reclaims storage nor governs the retention window.
Why C is correct: VACUUM physically removes data files that are no longer referenced by the Delta log and are older than the stated retention, so a seven-day retention reclaims the obsolete OPTIMIZE leftovers while preserving the required seven days of time travel.
Why D is wrong: Changing the log retention property affects metadata cleanup expectations but does not itself physically delete data files; a VACUUM operation is what removes the unreferenced data files from storage.