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MLS-C01 Data Engineering Practice Question

This MLS-C01 practice question tests your understanding of data engineering. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 engineer uses AWS Glue to run ETL jobs that transform data from JSON to Parquet. The job runs successfully but takes 30 minutes longer than expected. CloudWatch metrics show high memory utilization and disk spills. What is the most likely cause?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

A
The number of DPUs is too low
Why wrong: While low DPUs could cause spills, the symptom of high memory utilization suggests skew rather than insufficient resources.
B
The sink bucket has insufficient I/O throughput
Why wrong: S3 scales automatically; I/O is rarely a bottleneck for write operations.
C
The source data format is too large
Why wrong: Large files are expected and Glue handles them; the issue is distribution.
D
The data is skewed and not evenly distributed across partitions
Data skew causes some tasks to take longer, leading to spills and increased runtime.

Full breakdown with real-world context →

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

✓

The data is skewed and not evenly distributed across partitions

High memory utilization and disk spills in AWS Glue indicate that the data is not evenly distributed across partitions, causing some executors to handle a disproportionate amount of data. This data skew leads to excessive spilling to disk as memory is exhausted, which significantly slows down the job. Option D directly addresses this root cause, as skewed data prevents efficient parallel processing.

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.

✗
The number of DPUs is too low
Why it's wrong here
While low DPUs could cause spills, the symptom of high memory utilization suggests skew rather than insufficient resources.
✗
The sink bucket has insufficient I/O throughput
Why it's wrong here
S3 scales automatically; I/O is rarely a bottleneck for write operations.
✗
The source data format is too large
Why it's wrong here
Large files are expected and Glue handles them; the issue is distribution.
✓
The data is skewed and not evenly distributed across partitions
Why this is correct
Data skew causes some tasks to take longer, leading to spills and increased runtime.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates often assume high memory usage means insufficient resources (DPUs) and choose Option A, but the real culprit is data skew causing inefficient resource utilization, not a lack of total compute capacity.

Detailed technical explanation

How to think about this question

Under the hood, AWS Glue uses Apache Spark, which partitions data into tasks that run on executors. When data is skewed, certain executors receive far more records than others, causing them to spill intermediate data to disk when the shuffle buffer overflows (spark.sql.adaptive.coalescePartitions.enabled can help but is not enabled by default). In practice, this often occurs when joining on a high-cardinality key with a long tail, such as a user_id column where a few users generate most of the events.

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.

TExam Day Tips

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 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

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this MLS-C01 question test?

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: The data is skewed and not evenly distributed across partitions — High memory utilization and disk spills in AWS Glue indicate that the data is not evenly distributed across partitions, causing some executors to handle a disproportionate amount of data. This data skew leads to excessive spilling to disk as memory is exhausted, which significantly slows down the job. Option D directly addresses this root cause, as skewed data prevents efficient parallel processing.

What should I do if I get this MLS-C01 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

Are there clue words in this question I should notice?

Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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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.