The answer is to query the data directly in Athena without any preprocessing. This is correct because Amazon Athena charges based on the amount of data scanned per query, and for a one-time query scanning 5 TB of a 10 TB dataset, there is no cheaper option than paying for that scan directly. Partitioning or converting to columnar formats like Parquet would reduce future costs but require upfront processing and storage overhead, making them inefficient for a single query. On the AWS Certified Machine Learning Specialty MLS-C01 exam, this question tests your understanding of cost optimization for ad-hoc analytics on S3 data, often appearing as a trap where you might over-engineer a solution with Redshift Spectrum or EMR, which incur cluster or compute costs for transient workloads. A key memory tip: for one-time queries, the cheapest path is the simplest path—let Athena scan what it needs and pay only for that scan, avoiding any preprocessing or infrastructure setup.
MLS-C01 Data Engineering Practice Question
This MLS-C01 practice question tests your understanding of data engineering. 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 data scientist needs to run a one-time query on 10 TB of data stored in S3 using Amazon Athena. The query scans 5 TB and returns a small result set. Which approach minimizes cost?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Query the data directly in Athena without any preprocessing
Athena charges based on data scanned. Partitioning and using columnar formats like Parquet reduce the amount of data scanned. Redshift Spectrum would require a cluster. EMR is more expensive for one-time queries.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Query the data directly in Athena without any preprocessing
Why this is correct
For a one-time query, scanning 5 TB at $5 per TB is $25, which is minimal compared to preprocessing costs.
Related concept
Read the scenario before looking for a memorised answer.
✗
Create an S3 Select query to filter data before Athena
Why it's wrong here
S3 Select is for object-level filtering, not for full SQL queries across many objects.
✗
Use Amazon Redshift Spectrum to query the data
Why it's wrong here
Redshift Spectrum requires a provisioned Redshift cluster, adding cost for a one-time query.
✗
Use AWS Glue to convert the data to Parquet format and repartition by date
Why it's wrong here
Conversion costs time and money; for a one-time query, it's cheaper to just query as-is.
Common exam traps
Common exam trap: answer the scenario, not the keyword
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
How to think about this question
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.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
What to study next
Got this wrong? Here's your next step.
Identify which MLS-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 Engineering — This question tests Data Engineering — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Query the data directly in Athena without any preprocessing — Athena charges based on data scanned. Partitioning and using columnar formats like Parquet reduce the amount of data scanned. Redshift Spectrum would require a cluster. EMR is more expensive for one-time queries.
What should I do if I get this MLS-C01 question wrong?
Identify which MLS-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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This MLS-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 MLS-C01 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.