The answer is to increase the reserved concurrency of the Lambda function to 50. This directly addresses the root cause: with a reserved concurrency of only 10, the function is throttling because it cannot process enough SQS messages in parallel to keep up with the queue’s backlog. Lambda’s reserved concurrency sets a hard limit on the number of simultaneous executions, and when SQS invokes the function, any excess invocations are throttled, causing the high throttles and low throughput you see in CloudWatch. On the AWS Certified Developer Associate DVA-C02 exam, this scenario tests your understanding of how Lambda concurrency and SQS event source mapping interact—specifically, that increasing reserved concurrency is the primary lever for reducing throttles and boosting throughput, not adjusting timeout or batch size. A common trap is to assume the 2-second processing time is the bottleneck, but the real issue is the concurrency ceiling. Memory tip: “Reserved concurrency is your throttle valve—open it wider to let more messages through.”
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.
A developer is monitoring an AWS Lambda function that is triggered by an Amazon SQS queue. The function's CloudWatch metrics show a high number of throttles. The function has a reserved concurrency of 10 and the SQS queue has a large backlog of messages. The function processes each message in about 2 seconds and has a timeout of 60 seconds. Which action will most effectively reduce the throttles and increase throughput?
Increase the reserved concurrency of the Lambda function to 50
Increasing reserved concurrency allows more concurrent executions, reducing the chance of throttling and enabling more messages to be processed in parallel.
B
Increase the batch size in the SQS event source mapping to 100
Why wrong: Larger batch size reduces number of invocations but can increase execution time; it does not directly address concurrent execution throttling.
C
Increase the function timeout to 120 seconds
Why wrong: Timeout does not affect throttling; it only allows longer execution per invocation.
D
Decrease the reserved concurrency to 5
Why wrong: Decreasing reserved concurrency would increase throttling and reduce throughput.
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 of the Lambda function to 50
The high throttles indicate that the Lambda function's reserved concurrency of 10 is insufficient to handle the incoming messages from the SQS queue. By increasing reserved concurrency to 50, you allow more concurrent executions, which reduces throttling and increases throughput. The function's 2-second processing time and 60-second timeout are not the bottleneck; the concurrency limit is.
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 of the Lambda function to 50
Why this is correct
Increasing reserved concurrency allows more concurrent executions, reducing the chance of throttling and enabling more messages to be processed in parallel.
Related concept
Read the scenario before looking for a memorised answer.
✗
Increase the batch size in the SQS event source mapping to 100
Why it's wrong here
Larger batch size reduces number of invocations but can increase execution time; it does not directly address concurrent execution throttling.
✗
Increase the function timeout to 120 seconds
Why it's wrong here
Timeout does not affect throttling; it only allows longer execution per invocation.
✗
Decrease the reserved concurrency to 5
Why it's wrong here
Decreasing reserved concurrency would increase throttling and reduce throughput.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may think increasing batch size or timeout will help, but they overlook that the root cause is the reserved concurrency cap, which directly limits the number of concurrent executions and is the primary driver of throttles.
Detailed technical explanation
How to think about this question
Reserved concurrency guarantees a set number of concurrent executions for a function, but it also acts as a hard limit. When the SQS queue has a large backlog, the Lambda service polls the queue in batches; with only 10 reserved concurrency, only 10 invocations can run simultaneously, causing subsequent requests to be throttled. Increasing reserved concurrency allows more concurrent polls and processing, directly reducing the backlog and throttling.
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
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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 of the Lambda function to 50 — The high throttles indicate that the Lambda function's reserved concurrency of 10 is insufficient to handle the incoming messages from the SQS queue. By increasing reserved concurrency to 50, you allow more concurrent executions, which reduces throttling and increases throughput. The function's 2-second processing time and 60-second timeout are not the bottleneck; the concurrency limit is.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A developer has an AWS Lambda function that processes messages from an Amazon SQS queue. The function is configured with a reserved concurrency of 5. Recently, the SQS queue has experienced a high volume of messages, and the developer notices that many invocations are being throttled, leading to increased processing time. What is the most likely cause of the throttling?
medium
A.The function's execution role lacks permissions to invoke the function.
✓ B.The reserved concurrency is too low, causing SQS to throttle Lambda invocations.
C.The SQS queue visibility timeout is set too high.
D.The Lambda function has a VPC configuration that causes cold starts.
Why B: The correct answer is B because reserved concurrency limits the maximum number of concurrent executions for a Lambda function. When the SQS queue has a high volume of messages, Lambda attempts to scale up to process them, but with a reserved concurrency of 5, it can only run 5 concurrent invocations. Any additional invocation requests are throttled with a 429 error, causing messages to remain in the queue and increasing processing time.
Last reviewed: Jun 11, 2026
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.