DP-750 Certification Practice Question #95

Question

A team wants to aggressively reclaim storage on a busy production Delta table that has long-running jobs writing to it throughout the day. An engineer proposes the following maintenance step, to be run during business hours:

```sql
-- Disable the safety check, then vacuum with zero retention
SET spark.databricks.delta.retentionDurationCheck.enabled = false;
VACUUM prod.fact_transactions RETAIN 0 HOURS;
```

**Proposed solution:** Running `VACUUM` with a 0-hour retention on this table risks breaking time travel and can corrupt results for concurrent readers and in-flight writers, so it should not be run this way on a busy production table.

Does this solution meet the goal?

Accepted Answer

A 0-hour retention removes the retention window entirely, so `VACUUM` can delete data files that are still being referenced by concurrent readers and uncommitted files produced by in-flight, long-running writers — risking failed reads and table corruption. It also destroys time travel to any earlier version because the historical files are gone. Databricks therefore ships the `retentionDurationCheck` safety check and recommends at least 7 days of retention; the proposed solution correctly identifies running `RETAIN 0 HOURS` on a busy production table as unsafe, so the answer is Yes.

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