The answer is that the allowed lateness is set too low, causing late records to be dropped. In Apache Flink, event time processing relies on watermarks to track progress; once the watermark passes the end of a tumbling window, any records arriving after that point are considered late and are discarded unless the window has been configured with a sufficient allowed lateness period. This directly explains why output is delayed and records are lost—the window closes too early, and late data has no chance to be included. On the AWS Certified Machine Learning Specialty MLS-C01 exam, this question tests your understanding of Flink’s watermark and window mechanics in Kinesis Data Analytics, a common scenario for real-time ML pipelines. A frequent trap is confusing idle sources or parallelism with lateness settings; remember that idle sources stall watermarks, but only allowed lateness controls how long the window waits for stragglers. Memory tip: think of “lateness” as a grace period—if it’s too low, late records get the boot.
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 company uses Amazon Kinesis Data Analytics for Apache Flink to process real-time clickstream data. The application uses event time and watermarks for windowed aggregations. The team notices that the output from tumbling windows is delayed, and many late records are being dropped. 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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The allowed lateness is set too low, causing late records to be discarded
Option B is correct because late records are dropped when the watermark has passed the window's end; increasing the allowed lateness gives more time for late records to arrive. Option A is wrong because idle sources cause watermarks to stall, not drop late records. Option C is wrong because checkpointing interval does not affect watermark progress. Option D is wrong because parallelism affects throughput, not watermark behavior.
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 checkpointing interval is too long, causing state to be lost
Why it's wrong here
Checkpointing interval affects failure recovery, not late record handling.
✗
The parallelism is too low, causing backpressure
Why it's wrong here
Backpressure affects throughput but does not cause late records to be dropped.
✗
The source is marking itself as idle, causing watermarks to stall
Why it's wrong here
Idle sources can cause watermarks to not advance, but the symptom is delayed windows, not dropping late records.
✓
The allowed lateness is set too low, causing late records to be discarded
Why this is correct
Low allowed lateness means records arriving after the watermark are dropped.
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
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 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 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: The allowed lateness is set too low, causing late records to be discarded — Option B is correct because late records are dropped when the watermark has passed the window's end; increasing the allowed lateness gives more time for late records to arrive. Option A is wrong because idle sources cause watermarks to stall, not drop late records. Option C is wrong because checkpointing interval does not affect watermark progress. Option D is wrong because parallelism affects throughput, not watermark behavior.
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.
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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Question Discussion
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