Question 140 of 1,711
DEA-C01 Data Operations and Support Practice Question
A data engineer is troubleshooting a slow-running Amazon Athena query on a large dataset stored in S3. The query scans many small files. Which TWO actions can improve query performance?
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
✓
Concatenate small files into larger files
Concatenating small files into larger files reduces the overhead of file listing and task scheduling, improving query performance. Option D is correct because partitioning the data by a frequently filtered column allows Athena to use partition pruning, scanning only relevant partitions and reducing the amount of data read. Option A is incorrect because increasing the number of small files increases overhead and worsens performance. Option B is incorrect because disabling S3 server-side encryption does not affect query performance. Option E is incorrect because converting from CSV to JSON does not improve query performance; columnar formats like Parquet or ORC would be beneficial.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Increase the number of files to increase parallelism
Why it's wrong here
Too many files hurt performance.
- ✗
Disable S3 server-side encryption
Why it's wrong here
Encryption has minimal performance impact.
- ✓
Concatenate small files into larger files
Why this is correct
Reduces file open overhead.
- ✓
Partition the data by a frequently filtered column
Why this is correct
Limits data scanned.
- ✗
Convert files from CSV to JSON
Why it's wrong here
JSON is not more efficient than CSV.
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
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Last reviewed: Jun 20, 2026
This DEA-C01 practice question is part of Courseiva's free Amazon Web Services 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 DEA-C01 exam.
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