DP-203 Practice Question: Secure, monitor, and optimize data storage and data processing
You are designing a data processing solution using Azure Databricks. The solution must use Delta Lake for ACID transactions and must optimize storage costs by automatically compacting small files. Which feature should you enable?
⚠ Common exam trap
DP-203 often tests the distinction between automatic table maintenance features (auto-optimize, optimized writes) and manual commands (OPTIMIZE, VACUUM, ZORDER), so candidates who see 'OPTIMIZE' and assume it means automatic compaction pick the wrong answer.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Enable auto-optimize on the Delta table.
Auto-optimize (also called Optimized Writes / auto compaction) is a Delta Lake table property that automatically compacts small files during writes, eliminating the need for manual OPTIMIZE jobs. It combines with optimized writes to reduce the small-file problem at ingestion time, directly lowering storage and query costs. This is the native, built-in feature designed for the stated requirement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Run OPTIMIZE command in a scheduled job.
Why it's wrong here
A scheduled OPTIMIZE job compacts files only at intervals you define, so compaction is not automatic and small files accumulate between runs. OPTIMIZE is the right tool when you accept batch compaction windows, for example nightly maintenance on a large Delta table.
- ✗
Set retention duration for vacuum to 7 days.
Why it's wrong here
Vacuum retention controls when deleted data files become eligible for physical removal; it neither detects nor merges small files, so storage is not compacted. Setting a retention period is correct when balancing time-travel rollback needs against reclaiming obsolete file storage.
- ✗
Enable Z-order indexing on the Delta table.
Why it's wrong here
Z-order indexing co-locates related data to speed filtered reads; it does not compact small files, which is what OPTIMIZE with auto compaction performs. It tempts because Z-order is a Delta Lake optimisation, and it would be correct when the requirement is faster queries on high-cardinality filter columns rather than storage-cost reduction.
- ✓
Enable auto-optimize on the Delta table.
Why this is correct
Auto-optimize automatically compacts small files during writes, removing the need for manual OPTIMIZE jobs while preserving Delta Lake ACID guarantees. This directly satisfies the storage-cost constraint by reducing many small files into larger ones without extra orchestration.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Microsoft exam blueprint
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