MLS-C01 Data Engineering Practice Question

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?

⚠ Common exam trap

It's easy for candidates to 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.

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.

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.
✗
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.

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

Go deeper

MLS-C01 Data Engineering Practice Question

Why each option matters

Option-by-option breakdown

AWS S3 Storage Class Comparison

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