DEA-C01 Lambda Batch Window Practice Question
A company is streaming clickstream data from a website into Amazon Kinesis Data Streams. The data is then consumed by a Lambda function that transforms the records and writes them to an S3 bucket in Parquet format. Recently, the Lambda function has been timing out and the S3 bucket is not receiving all expected records. The Kinesis stream has a shard count of 10 and the Lambda function's reserved concurrency is set to the default. Which change would MOST likely resolve the issue?
⚠ Common exam trap
Candidates often think that increasing batch size or concurrency will improve throughput, but when functions are timing out, reducing the batch size (or batch window) is the correct fix. Increasing concurrency does not help per-invocation timeouts.
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
✓
Decrease the batch window from the default 300 seconds to 60 seconds.
The Lambda function is timing out because it cannot process the default batch of 100 records within the function timeout. Decreasing the batch window from 300 seconds to 60 seconds causes Lambda to invoke more frequently with smaller batches, reducing the number of records per invocation. This lowers the processing time per invocation, helping the function complete before the timeout. Increasing the batch size (Option D) would worsen the issue by adding more records per invocation. Increasing reserved concurrency (Option C) does not reduce per-invocation processing time. Using a delivery stream (Option B) changes the architecture unnecessarily and may not preserve the transformation logic.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Decrease the batch window from the default 300 seconds to 60 seconds.
Why this is correct
Correct: Decreasing the batch window reduces the number of records per invocation, which helps the Lambda function complete within its timeout.
- ✗
Configure the Kinesis stream to directly write to S3 using a delivery stream.
Why it's wrong here
Not the best choice: Using Kinesis Firehose to write directly to S3 bypasses the Lambda transformation, which is required. Firehose can invoke Lambda but adds complexity and doesn't directly address the timeout.
- ✗
Increase the Lambda function's reserved concurrency.
Why it's wrong here
Not correct: Increasing reserved concurrency allows more concurrent invocations but does not reduce the processing time of each invocation, so timeouts would persist.
- ✗
Increase the batch size from the default 100 to 500 records per invocation.
Why it's wrong here
Not correct: Increasing the batch size from 100 to 500 would increase the number of records per invocation, making the timeout worse as the function has more data to process.
Visual reference
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 |
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DEA-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 DEA-C01 exam.