MLS-C01 Data Engineering Practice Question
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?
⚠ Common exam trap
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.
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.
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.
- ✗
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.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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