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.
Which THREE of the following are best practices for optimizing performance of Amazon EMR clusters? (Choose 3)
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Consolidate small files into larger ones before processing
Option B is correct because consolidating small files into larger ones before processing on Amazon EMR reduces the overhead of the Hadoop Distributed File System (HDFS) metadata operations. Each small file consumes a block of memory in the NameNode, and processing many small files leads to excessive task launches and I/O overhead, degrading performance. Using tools like `s3-dist-cp` to combine files into fewer, larger blocks improves throughput and reduces job execution time.
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.
✗
Use Spot Instances for task nodes
Why it's wrong here
Again cost, not performance.
✓
Consolidate small files into larger ones before processing
Why this is correct
Consolidation reduces overhead and improves performance.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✓
Enable EBS optimization on EC2 instances
Why this is correct
EBS optimization improves disk I/O performance.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use Spot Instances to reduce costs
Why it's wrong here
Spot instances reduce cost, not necessarily performance.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse cost optimization strategies (like Spot Instances) with performance optimization, leading them to select options A or E even though the question explicitly asks for performance best practices.
Detailed technical explanation
How to think about this question
Under the hood, HDFS stores files as blocks (default 128 MB), and the NameNode keeps metadata for each block in memory. With many small files, the NameNode memory is exhausted, leading to slower metadata operations and increased garbage collection pauses. Consolidation reduces the number of blocks, improving MapReduce and Spark task scheduling efficiency. In real-world scenarios, processing log files from IoT devices or web servers often generates millions of tiny files, making consolidation critical for EMR job performance.
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 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 exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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: Consolidate small files into larger ones before processing — Option B is correct because consolidating small files into larger ones before processing on Amazon EMR reduces the overhead of the Hadoop Distributed File System (HDFS) metadata operations. Each small file consumes a block of memory in the NameNode, and processing many small files leads to excessive task launches and I/O overhead, degrading performance. Using tools like `s3-dist-cp` to combine files into fewer, larger blocks improves throughput and reduces job execution time.
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: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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.
Question Discussion
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