Quick Answer
The correct answer involves three key factors: using S3 Select to filter data server-side, storing data in compressed formats like GZIP or Snappy, and using larger object sizes to maximize parallel throughput. S3 Select reduces the amount of data transferred by pushing down filtering logic to the S3 service, compression minimizes network transfer volume, and larger objects allow EMR to issue more concurrent range requests, each improving read performance. On the AWS Certified Data Engineer Associate DEA-C01 exam, this question tests your understanding of how S3 read performance factors interact with distributed processing frameworks like Spark on EMR. A common trap is confusing upload accelerators or object lock settings with read optimization—remember that S3 Transfer Acceleration only helps writes, not reads. For a quick memory tip: think of the three S’s—Select, Size, and Snappy—as the core levers for faster S3 reads.
This DEA-C01 practice question tests your understanding of data operations and support. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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.)
Use of S3 Transfer Acceleration.
Why wrong: Transfer Acceleration is for uploads, not reads.
Use of S3 Select to retrieve only a subset of data.
S3 Select reduces the amount of data transferred.
Use of S3 Object Lock.
Why wrong: Object Lock does not affect performance.
Average object size in S3 bucket.
Larger objects allow better parallelization.
Data stored in compressed format (e.g., GZIP, Snappy).
Compressed data reduces I/O.
Answer choices
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 A, C, and D are correct. A: S3 Select can reduce data scanned. C: Data compression reduces network transfer. D: Larger object sizes improve throughput due to parallel requests. Option B is wrong because S3 Transfer Acceleration improves upload speed, not read performance. Option E is wrong because S3 Object Lock does not affect read performance.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
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
Transfer Acceleration is for uploads, not reads.
Use of S3 Select to retrieve only a subset of data.
Why this is correct
S3 Select reduces the amount of data transferred.
Related concept
Read the scenario before looking for a memorised answer.
Use of S3 Object Lock.
Why it's wrong here
Object Lock does not affect performance.
Average object size in S3 bucket.
Why this is correct
Larger objects allow better parallelization.
Related concept
Read the scenario before looking for a memorised answer.
Data stored in compressed format (e.g., GZIP, Snappy).
Why this is correct
Compressed data reduces I/O.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Identify which DEA-C01 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Data Operations and Support — study guide chapter
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FAQ
Data Operations and Support — This question tests Data Operations and Support — Read the scenario before looking for a memorised answer..
The correct answer is: Use of S3 Select to retrieve only a subset of data. — Options A, C, and D are correct. A: S3 Select can reduce data scanned. C: Data compression reduces network transfer. D: Larger object sizes improve throughput due to parallel requests. Option B is wrong because S3 Transfer Acceleration improves upload speed, not read performance. Option E is wrong because S3 Object Lock does not affect read performance.
Identify which DEA-C01 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Read the scenario before looking for a memorised answer.
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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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