DEA-C01 S3 Select Practice Question
A company uses Amazon EMR to run Spark jobs on data stored in Amazon S3. The data engineer notices that the jobs are running slower than expected. The engineer suspects that the S3 storage class might be affecting performance. Which THREE factors can impact read performance from S3? (Choose three.)
⚠ Common exam trap
A common mistake is thinking S3 Transfer Acceleration improves read performance, but it only speeds up uploads.
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
✓
Use of S3 Select to retrieve only a subset of data.
Options B, D, and E are correct. B: S3 Select can retrieve only a subset of data, reducing the amount scanned and improving read performance. D: Larger average object sizes allow better throughput by leveraging parallel requests and reducing overhead. E: Storing data in compressed formats reduces the amount of data transferred, improving read performance. Option A is incorrect because S3 Transfer Acceleration is designed to improve upload speed over long distances, not read performance. Option C is incorrect because S3 Object Lock prevents object deletion or overwrite but does not affect read performance.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use of S3 Transfer Acceleration.
Why it's wrong here
S3 Transfer Acceleration improves upload speed, not read performance, so it does not factor into read performance issues.
- ✓
Use of S3 Select to retrieve only a subset of data.
Why this is correct
S3 Select can retrieve only a subset of data (e.g., using SQL expressions), reducing data scanned and improving read performance.
- ✗
Use of S3 Object Lock.
Why it's wrong here
S3 Object Lock prevents object deletion or overwrites; it does not affect read performance.
- ✓
Average object size in S3 bucket.
Why this is correct
Average object size affects read performance because larger objects allow more efficient parallel reads and better throughput.
- ✓
Data stored in compressed format (e.g., GZIP, Snappy).
Why this is correct
Compressed data reduces the amount of data transferred from S3, improving read performance.
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 |
Go deeper
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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