- A
Decrease the batch window from the default 300 seconds to 60 seconds.
Correct: Decreasing the batch window reduces the number of records per invocation, which helps the Lambda function complete within its timeout.
- B
Configure the Kinesis stream to directly write to S3 using a delivery stream.
Why wrong: 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.
- C
Increase the Lambda function's reserved concurrency.
Why wrong: Not correct: Increasing reserved concurrency allows more concurrent invocations but does not reduce the processing time of each invocation, so timeouts would persist.
- D
Increase the batch size from the default 100 to 500 records per invocation.
Why wrong: 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.
Resolving Lambda Timeouts When Processing Kinesis Data Streams by Increasing the Batch Size
This DEA-C01 practice question tests your understanding of data ingestion and transformation. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: lambda Batch Window. 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 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?
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 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.
Key principle: Lambda Batch Window
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.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Lambda Batch Window
- ✗
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
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.
Detailed technical explanation
How to think about this question
Kinesis Data Streams uses a shard-based model where each shard can process up to 1,000 records per second. Lambda integrates with Kinesis via event source mappings, which poll shards and invoke the function with a batch of records. The default batch size is 100, and increasing it to 500 reduces the number of invocations per shard, allowing the function to process more records per invocation and better utilize the 15-minute timeout. This is particularly effective when the transformation logic is lightweight but the overhead of invocation setup is high.
KKey Concepts to Remember
- Lambda Batch Window
- Lambda Timeout
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
Lambda Batch Window
Real-world example
How this comes up in practice
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
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 |
What to study next
Got this wrong? Here's your next step.
Review lambda Batch Window, then practise related DEA-C01 questions on the same topic to reinforce the concept.
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Data Ingestion and Transformation — study guide chapter
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FAQ
Questions learners often ask
What does this DEA-C01 question test?
Data Ingestion and Transformation — This question tests Data Ingestion and Transformation — Lambda Batch Window.
What is the correct answer to this question?
The correct answer is: 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.
What should I do if I get this DEA-C01 question wrong?
Review lambda Batch Window, then practise related DEA-C01 questions on the same topic to reinforce the concept.
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?
Lambda Batch Window
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Last reviewed: Jul 4, 2026
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