Databricks-DE-Pro Developing Code (Python/SQL) Practice Question
Which of the following describes the behavior of the 'OPTIMIZE' command in Databricks?
⚠ Common exam trap
Examinees frequently confuse 'OPTIMIZE' with data cleaning or deduplication operations, ignoring its exact function of file compaction and layout improvement.
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
✓
It rewrites data files into a more efficient layout for reads.
The 'OPTIMIZE' command performs file compaction, which consolidates small files into larger, optimally sized files. This improves scan performance significantly by reducing the metadata overhead of opening and reading many tiny files. It also supports Z-Ordering, which co-locates related data in the same files, further enhancing the efficiency of data skipping and improving query speed for common filter predicates.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
It recomputes statistics to improve query planning.
Why it's wrong here
While OPTIMIZE does update statistics, its primary purpose is file compaction and data layout optimization. ANALYZE TABLE is the command specifically designed to compute and update statistics for the cost-based optimizer, and they serve distinct purposes in table maintenance.
- ✓
It rewrites data files into a more efficient layout for reads.
Why this is correct
OPTIMIZE rewrites the underlying Parquet files to be more efficiently sized, addressing the 'small file problem.' By compacting many small files into larger ones, it reduces the I/O overhead for readers and optimizes the file layout, which is essential for maintaining query performance in Delta tables.
- ✗
It clears the transaction log to reduce storage costs.
Why it's wrong here
The transaction log is critical for Delta Lake's ACID properties and cannot be simply cleared. Vacuuming removes old data files, but not the transaction log itself. Clearing the log would corrupt the table and prevent time-travel, so this is not a function of the OPTIMIZE command.
- ✗
It converts non-Delta tables to Delta format.
Why it's wrong here
The CONVERT TO DELTA command is used to transition existing Parquet tables to Delta Lake. OPTIMIZE is a maintenance operation that can only be run on tables that are already in the Delta Lake format, so it cannot perform the conversion task.
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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 Databricks exam blueprint
This Databricks-DE-Pro practice question is part of Courseiva's free Databricks certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the Databricks-DE-Pro exam.