- A
The function's execution role lacks permissions to invoke the function.
Why wrong: The execution role grants permissions to other AWS services, not to invoke the function itself. Throttling is unrelated to IAM permissions.
- B
The reserved concurrency is too low, causing SQS to throttle Lambda invocations.
Reserved concurrency caps the number of concurrent executions. When the queue has many messages, SQS tries to invoke Lambda concurrently, but if the reserved limit is reached, invocations are throttled, delaying processing.
- C
The SQS queue visibility timeout is set too high.
Why wrong: Visibility timeout controls how long a message is hidden after being received. A high value only delays reprocessing of failed messages; it does not cause throttling.
- D
The Lambda function has a VPC configuration that causes cold starts.
Why wrong: Cold starts add latency to the first invocation but are not the primary cause of throttling. VPC configuration does not directly limit the number of concurrent executions.
DVA-C02 Troubleshooting and Optimization Practice Question
This DVA-C02 practice question tests your understanding of troubleshooting and optimization. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. A key principle to apply: reserved concurrency sets a hard upper limit on concurrent Lambda executions.. 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 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?
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
The reserved concurrency is too low, causing SQS to throttle Lambda invocations.
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.
Key principle: Reserved concurrency sets a hard upper limit on concurrent Lambda executions.
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 function's execution role lacks permissions to invoke the function.
Why it's wrong here
The execution role grants permissions to other AWS services, not to invoke the function itself. Throttling is unrelated to IAM permissions.
- ✓
The reserved concurrency is too low, causing SQS to throttle Lambda invocations.
Why this is correct
Reserved concurrency caps the number of concurrent executions. When the queue has many messages, SQS tries to invoke Lambda concurrently, but if the reserved limit is reached, invocations are throttled, delaying processing.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Reserved concurrency sets a hard upper limit on concurrent Lambda executions.
- ✗
The SQS queue visibility timeout is set too high.
Why it's wrong here
Visibility timeout controls how long a message is hidden after being received. A high value only delays reprocessing of failed messages; it does not cause throttling.
- ✗
The Lambda function has a VPC configuration that causes cold starts.
Why it's wrong here
Cold starts add latency to the first invocation but are not the primary cause of throttling. VPC configuration does not directly limit the number of concurrent executions.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse throttling (due to concurrency limits) with cold starts (due to VPC or initialization delays), or they mistakenly think that SQS itself throttles Lambda invocations rather than understanding that Lambda's reserved concurrency is the bottleneck.
Detailed technical explanation
How to think about this question
Lambda's scaling behavior for SQS-triggered functions uses a 'polling' model where the Lambda service polls the SQS queue and invokes the function with batches of messages. With reserved concurrency set to 5, the Lambda service will only maintain up to 5 concurrent pollers, and any additional messages in the queue will not be processed until a poller becomes free. This is different from unreserved concurrency, where Lambda can scale up to 1,000 concurrent executions (regional default) based on the queue depth.
KKey Concepts to Remember
- Reserved concurrency sets a hard upper limit on concurrent Lambda executions.
- SQS attempts to invoke Lambda concurrently to process messages.
- Exceeding reserved concurrency causes Lambda to throttle invocations.
- Throttling leads to increased message processing time and delays.
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
Reserved concurrency sets a hard upper limit on concurrent Lambda executions.
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.
Review reserved concurrency sets a hard upper limit on concurrent Lambda executions., then practise related DVA-C02 questions on the same topic to reinforce the concept.
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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 — Reserved concurrency sets a hard upper limit on concurrent Lambda executions..
What is the correct answer to this question?
The correct answer is: The reserved concurrency is too low, causing SQS to throttle Lambda invocations. — 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.
What should I do if I get this DVA-C02 question wrong?
Review reserved concurrency sets a hard upper limit on concurrent Lambda executions., then practise related DVA-C02 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?
Reserved concurrency sets a hard upper limit on concurrent Lambda executions.
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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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