- A
Increase the reserved concurrency to 20.
Increasing reserved concurrency allows Lambda to scale and invoke more function instances concurrently. This directly reduces throttling and allows the function to process more messages from the SQS queue simultaneously, improving throughput and reducing backlog.
- B
Increase the batch size to 100.
Why wrong: Increasing batch size may cause each invocation to take longer, potentially leading to timeouts if the function cannot process 100 messages within its timeout. It does not address the underlying concurrency limitation and may even increase throttling because fewer invocations happen but each takes longer.
- C
Decrease the reserved concurrency to 2.
Why wrong: Decreasing reserved concurrency would make throttling worse by further limiting the number of concurrent executions. This would increase the backlog.
- D
Increase the provisioned write capacity of the DynamoDB table.
Why wrong: The issue is Lambda throttling, not DynamoDB throttling. Increasing DynamoDB capacity does not help Lambda process more messages. It may become relevant later if DynamoDB becomes a bottleneck, but the immediate problem is Lambda throttling.
Quick Answer
The answer is to increase the reserved concurrency to 20. This directly resolves Lambda throttling because the current reserved concurrency of 5 caps concurrent executions, limiting throughput to just 50 messages per second with a batch size of 10 and 1-second execution time. Raising reserved concurrency to 20 allows 20 concurrent invocations, boosting throughput to 200 messages per second and clearing the SQS backlog. On the AWS Certified Developer Associate DVA-C02 exam, this scenario tests your understanding of how reserved concurrency acts as a hard throttle—a common trap is confusing it with provisioned concurrency or trying to reduce batch size, which would lower throughput. Remember that reserved concurrency sets a strict ceiling; increasing it is the most effective fix when throttling is the bottleneck. Memory tip: think “reserved = restricted”—if you see throttling, you need to raise the reserved limit, not lower the batch size.
DVA-C02 Troubleshooting and Optimization Practice Question
This DVA-C02 practice question tests your understanding of troubleshooting and optimization. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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.
An AWS Lambda function processes messages from an Amazon SQS queue and writes results to an Amazon DynamoDB table. The function is configured with a reserved concurrency of 5 and a batch size of 10. CloudWatch metrics show high throttling and a growing queue backlog. The function's execution time averages 1 second per message. What is the MOST effective action to reduce throttling while improving throughput?
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
Increase the reserved concurrency to 20.
The Lambda function is throttling because its reserved concurrency of 5 limits it to 5 concurrent executions. With a batch size of 10 and 1-second execution time, the function can process at most 5 * 10 = 50 messages per second. Increasing reserved concurrency to 20 allows 20 concurrent executions, raising throughput to 200 messages per second, which directly reduces throttling and clears the backlog.
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.
- ✓
Increase the reserved concurrency to 20.
Why this is correct
Increasing reserved concurrency allows Lambda to scale and invoke more function instances concurrently. This directly reduces throttling and allows the function to process more messages from the SQS queue simultaneously, improving throughput and reducing backlog.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Increase the batch size to 100.
Why it's wrong here
Increasing batch size may cause each invocation to take longer, potentially leading to timeouts if the function cannot process 100 messages within its timeout. It does not address the underlying concurrency limitation and may even increase throttling because fewer invocations happen but each takes longer.
- ✗
Decrease the reserved concurrency to 2.
Why it's wrong here
Decreasing reserved concurrency would make throttling worse by further limiting the number of concurrent executions. This would increase the backlog.
- ✗
Increase the provisioned write capacity of the DynamoDB table.
Why it's wrong here
The issue is Lambda throttling, not DynamoDB throttling. Increasing DynamoDB capacity does not help Lambda process more messages. It may become relevant later if DynamoDB becomes a bottleneck, but the immediate problem is Lambda throttling.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may confuse Lambda throttling with downstream resource throttling (like DynamoDB) and choose to increase write capacity, or they may think increasing batch size alone will solve the problem without considering the concurrency bottleneck.
Detailed technical explanation
How to think about this question
Lambda reserved concurrency acts as a hard limit on concurrent executions, and when exceeded, requests are throttled with a 429 error. The SQS event source mapping polls the queue and invokes Lambda with batches, but if concurrency is exhausted, messages remain in the queue, causing backlog growth. In real-world scenarios, Lambda's scaling behavior is also influenced by the number of shards in a Kinesis stream or partitions in an SQS queue, but here the simple fix is to increase reserved concurrency to match the desired throughput.
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 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.
What to study next
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FAQ
Questions learners often ask
What does this DVA-C02 question test?
Troubleshooting and Optimization — This question tests Troubleshooting and Optimization — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Increase the reserved concurrency to 20. — The Lambda function is throttling because its reserved concurrency of 5 limits it to 5 concurrent executions. With a batch size of 10 and 1-second execution time, the function can process at most 5 * 10 = 50 messages per second. Increasing reserved concurrency to 20 allows 20 concurrent executions, raising throughput to 200 messages per second, which directly reduces throttling and clears the backlog.
What should I do if I get this DVA-C02 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: Jun 11, 2026
This DVA-C02 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 DVA-C02 exam.
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