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Data Engineering →hardMultiple ChoiceObjective-mapped

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.

Network Topology

Refer to the exhibit. A company is using the Kinesis stream 'my-stream' with one shard. The producer is sending 1000 records per second, each 1 KB. The consumer is reading from the stream using the Kinesis Client Library (KCL). The consumer is able to process 500 records per second per shard. What is the most likely cause of the consumer falling behind?

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.

Network Topology

A
The retention period is set to 24 hours, which is too short.
Why wrong: The retention period is not the cause. A 24-hour retention period is standard and does not affect throughput or cause the consumer to fall behind.
B
The stream uses KMS encryption, which adds latency.
KMS encryption adds latency for both producer and consumer. Since the consumer is processing at half the producer rate, decryption overhead is a likely contributor to the consumer falling behind.
C
The stream has only one shard, which limits the read throughput to 1 MB/s.
Why wrong: Incorrect. The shard's read throughput limit is 2 MB/s, not 1 MB/s. The producer is sending 1 MB/s, which is within the shard's read capacity, so this option is factually wrong.
D
The consumer application is not using enhanced fan-out.
Why wrong: Enhanced fan-out provides dedicated throughput for multiple consumers. With only one consumer, it does not improve performance; the consumer already has exclusive access to the shard's read throughput.

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 stream uses KMS encryption, which adds latency.

The consumer is processing 500 records per second per shard, which is half the producer's rate of 1000 records per second. While the shard's read throughput limit is 2 MB/s, not 1 MB/s, the consumer's processing speed is the bottleneck. Among the options, KMS encryption is the most plausible cause because decryption latency can significantly slow down the consumer, especially if the consumer application is not optimized for encryption overhead.

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 retention period is set to 24 hours, which is too short.
Why it's wrong here
The retention period is not the cause. A 24-hour retention period is standard and does not affect throughput or cause the consumer to fall behind.
✓
The stream uses KMS encryption, which adds latency.
Why this is correct
KMS encryption adds latency for both producer and consumer. Since the consumer is processing at half the producer rate, decryption overhead is a likely contributor to the consumer falling behind.
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.
✗
The stream has only one shard, which limits the read throughput to 1 MB/s.
Why it's wrong here
Incorrect. The shard's read throughput limit is 2 MB/s, not 1 MB/s. The producer is sending 1 MB/s, which is within the shard's read capacity, so this option is factually wrong.
✗
The consumer application is not using enhanced fan-out.
Why it's wrong here
Enhanced fan-out provides dedicated throughput for multiple consumers. With only one consumer, it does not improve performance; the consumer already has exclusive access to the shard's read throughput.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Candidates often mistake the shard's read throughput limit as 1 MB/s (the write limit) rather than the actual 2 MB/s. In this scenario, the shard is not the bottleneck; the consumer's processing rate is lower due to factors like KMS encryption latency.

Detailed technical explanation

How to think about this question

Kinesis shards provide a fixed write throughput of 1 MB/s or 1000 records per second and a read throughput of 2 MB/s or 5 transactions per second. The KCL uses a single worker per shard by default, and each worker processes records sequentially with a configurable maxRecordsPerSecond (default 1000). In this scenario, the consumer's processing rate of 500 records per second is likely due to application logic or resource constraints, not the shard's throughput limit. Real-world scenarios often involve consumers that perform heavy transformations or write to slow downstream systems, causing backpressure even when shard capacity is sufficient.

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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.

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 stream uses KMS encryption, which adds latency. — The consumer is processing 500 records per second per shard, which is half the producer's rate of 1000 records per second. While the shard's read throughput limit is 2 MB/s, not 1 MB/s, the consumer's processing speed is the bottleneck. Among the options, KMS encryption is the most plausible cause because decryption latency can significantly slow down the consumer, especially if the consumer application is not optimized for encryption overhead.

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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