- A
The S3 bucket is not configured with versioning, causing overwrites.
Why wrong: S3 versioning does not affect order of writes; it only keeps history.
- B
The Lambda function is reading from the oldest sequence number, causing high IteratorAgeSeconds.
Why wrong: This would cause latency but not out-of-order writes.
- C
The Lambda function’s reserved concurrency is too low for the increased shard count.
Why wrong: Lambda concurrency can be increased, but it does not cause out-of-order writes.
- D
The partition key used by the producer does not ensure that related records go to the same shard after resharding.
After resharding, the mapping of partition keys to shards changes. If ordering matters, the partition key must be chosen to keep related records together.
Quick Answer
The answer is that the partition key used by the producer does not ensure related records go to the same shard after resharding. This is the most likely cause because when a Kinesis stream is resharded—for example, from 2 to 4 shards—the hash key range for each shard is split, meaning the same partition key may now map to a different shard than before. As a result, records that were previously ordered within a single shard (such as all events from one user session) can be distributed across multiple shards, and since each shard is consumed independently by Lambda, those related records arrive out of order and with increased latency. On the AWS Certified Machine Learning Specialty MLS-C01 exam, this scenario tests your understanding of how Kinesis shard architecture and partition key design affect data ordering, a common trap where candidates blame Lambda scaling or S3 write behavior instead. A helpful memory tip: “Same key, same shard—after resharding, check the mapping.”
MLS-C01 Data Engineering Practice Question
This MLS-C01 practice question tests your understanding of data engineering. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 Kinesis Data Streams to ingest real-time clickstream data from a website. The data is consumed by a Lambda function that writes records to an S3 bucket. Recently, the number of shards was increased from 2 to 4 to handle higher throughput. After the change, the Lambda function started processing records with increased latency and some records were being written out of order. 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.
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 partition key used by the producer does not ensure that related records go to the same shard after resharding.
Option D is correct because after resharding from 2 to 4 shards, the mapping of partition keys to shards changes. If the producer does not use a partition key that ensures related records (e.g., same user session) are routed to the same shard, records that were previously ordered within a shard may now be split across multiple shards. Since the Lambda consumer processes shards independently, records from the same logical sequence can arrive out of order, and the increased shard count can also cause higher latency if the consumer is not properly parallelized.
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 S3 bucket is not configured with versioning, causing overwrites.
Why it's wrong here
S3 versioning does not affect order of writes; it only keeps history.
- ✗
The Lambda function is reading from the oldest sequence number, causing high IteratorAgeSeconds.
Why it's wrong here
This would cause latency but not out-of-order writes.
- ✗
The Lambda function’s reserved concurrency is too low for the increased shard count.
Why it's wrong here
Lambda concurrency can be increased, but it does not cause out-of-order writes.
- ✓
The partition key used by the producer does not ensure that related records go to the same shard after resharding.
Why this is correct
After resharding, the mapping of partition keys to shards changes. If ordering matters, the partition key must be chosen to keep related records together.
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 confuse increased shard count with a need for more concurrency (Option C), but the real issue is that resharding changes the partition-to-shard mapping, which can break ordering guarantees unless the producer explicitly handles the new hash range.
Detailed technical explanation
How to think about this question
Kinesis Data Streams uses the partition key to hash to a specific shard; after resharding (split or merge), the hash key range is redistributed, so the same partition key may map to a different shard than before. This means that records with the same partition key written before and after resharding can end up in different shards, breaking per-key ordering. Lambda processes each shard sequentially, so records from the same logical sequence that land in different shards are processed independently and can be written to S3 out of order.
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.
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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 partition key used by the producer does not ensure that related records go to the same shard after resharding. — Option D is correct because after resharding from 2 to 4 shards, the mapping of partition keys to shards changes. If the producer does not use a partition key that ensures related records (e.g., same user session) are routed to the same shard, records that were previously ordered within a shard may now be split across multiple shards. Since the Lambda consumer processes shards independently, records from the same logical sequence can arrive out of order, and the increased shard count can also cause higher latency if the consumer is not properly parallelized.
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.
About these practice questions
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Last reviewed: Jun 11, 2026
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.
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