- A
The source Kinesis stream has insufficient shards.
Why wrong: Shard count affects throughput, not delivery interval.
- B
The buffer size is set to a value larger than the incoming data rate.
If the buffer size is large and data rate low, Firehose waits longer.
- C
The S3 bucket is in a different region.
Why wrong: Cross-region delivery may add latency but not fixed 5-minute intervals.
- D
The IAM role does not have permission to write to S3.
Why wrong: Permission errors would cause failures, not delays.
Question 320 of 1,755
Why Kinesis Firehose Delivers Data Later Than Buffer Interval Set
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 Firehose to deliver streaming data to Amazon S3. They notice that the data is delivered in 5-minute intervals even though they set the buffer interval to 60 seconds. What could be the cause?
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 buffer size is set to a value larger than the incoming data rate.
B is correct because Kinesis Data Firehose delivers data based on whichever condition is met first: the buffer interval (60 seconds) or the buffer size (e.g., 5 MB). If the incoming data rate is very low, the buffer size threshold may never be reached within 60 seconds, causing Firehose to wait longer—up to the maximum buffer interval of 900 seconds—before delivering. In this case, the data rate is so low that it takes 5 minutes to fill the buffer, overriding the 60-second interval setting.
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 source Kinesis stream has insufficient shards.
Why it's wrong here
Shard count affects throughput, not delivery interval.
- ✓
The buffer size is set to a value larger than the incoming data rate.
Why this is correct
If the buffer size is large and data rate low, Firehose waits longer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The S3 bucket is in a different region.
Why it's wrong here
Cross-region delivery may add latency but not fixed 5-minute intervals.
- ✗
The IAM role does not have permission to write to S3.
Why it's wrong here
Permission errors would cause failures, not delays.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume the buffer interval is a strict timer, but Firehose actually uses a 'first-trigger' model where the buffer size can override the interval, causing longer delivery delays than expected.
Detailed technical explanation
How to think about this question
Kinesis Data Firehose uses two independent thresholds for batching: `BufferSizeInMBs` (default 5 MB, range 1–128 MB) and `BufferIntervalInSeconds` (default 300 seconds, range 60–900 seconds). Delivery occurs when either threshold is met. In low-throughput scenarios, the buffer size fills slowly, so the buffer interval becomes the dominant factor—but only if the interval is set lower than the time needed to fill the buffer. If the interval is set to 60 seconds but the buffer never fills, Firehose will still wait up to the maximum allowed interval (900 seconds) unless the buffer size is reached. This behavior is documented in the AWS Firehose API reference.
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.
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
What to study next
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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 buffer size is set to a value larger than the incoming data rate. — B is correct because Kinesis Data Firehose delivers data based on whichever condition is met first: the buffer interval (60 seconds) or the buffer size (e.g., 5 MB). If the incoming data rate is very low, the buffer size threshold may never be reached within 60 seconds, causing Firehose to wait longer—up to the maximum buffer interval of 900 seconds—before delivering. In this case, the data rate is so low that it takes 5 minutes to fill the buffer, overriding the 60-second interval setting.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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