The correct answer is to implement idempotent processing by checking a condition expression in DynamoDB PutItem. This works because SQS offers at-least-once delivery, meaning the same message can be sent to your Lambda function multiple times, leading to duplicate DynamoDB writes. By using a unique deduplication identifier—such as the SQS message ID or a business-specific key—as a condition in your PutItem call (e.g., attribute_not_exists(OrderId)), you ensure that only the first write succeeds, and subsequent attempts are silently ignored. On the AWS Certified Developer Associate DVA-C02 exam, this scenario tests your understanding of how to handle non-idempotent triggers in event-driven architectures; a common trap is to assume that SQS FIFO queues alone solve duplicates, but they only guarantee ordering and deduplication within the queue, not after Lambda processing. Remember the memory tip: “Condition before insertion, not after detection”—always prevent the duplicate write at the database level rather than trying to clean it up later.
DVA-C02 Troubleshooting and Optimization Practice Question
This DVA-C02 practice question tests your understanding of troubleshooting and optimization. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 notices that an application is generating duplicate entries in a DynamoDB table. The application uses a Lambda function triggered by an SQS queue. Messages are processed with at-least-once delivery. Which design change will reduce duplicates?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "least"
Why it matters: You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
Why wrong: Visibility timeout prevents other consumers from seeing the message, but does not prevent duplicates from redelivery.
B
Use a FIFO SQS queue with content-based deduplication.
Why wrong: FIFO ensures exactly-once processing, but the question asks for reducing duplicates with at-least-once; idempotency is a more direct solution.
C
Use DynamoDB Transactions to ensure atomic writes.
Why wrong: Transactions don't prevent duplicate messages; they ensure atomicity across items.
D
Implement idempotent processing by checking a condition expression in DynamoDB PutItem.
Idempotent writes using ConditionExpression prevent duplicate inserts.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Implement idempotent processing by checking a condition expression in DynamoDB PutItem.
SQS provides at-least-once delivery, so duplicates are possible. Making the Lambda function idempotent using a unique message deduplication ID (e.g., using the message ID as a condition in DynamoDB) prevents duplicates.
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 visibility timeout of the SQS queue.
Why it's wrong here
Visibility timeout prevents other consumers from seeing the message, but does not prevent duplicates from redelivery.
✗
Use a FIFO SQS queue with content-based deduplication.
Why it's wrong here
FIFO ensures exactly-once processing, but the question asks for reducing duplicates with at-least-once; idempotency is a more direct solution.
✗
Use DynamoDB Transactions to ensure atomic writes.
Why it's wrong here
Transactions don't prevent duplicate messages; they ensure atomicity across items.
✓
Implement idempotent processing by checking a condition expression in DynamoDB PutItem.
Why this is correct
Idempotent writes using ConditionExpression prevent duplicate inserts.
Clue confirmation
The clue word "least" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
Got this wrong? Here's your next step.
Identify which DVA-C02 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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: Implement idempotent processing by checking a condition expression in DynamoDB PutItem. — SQS provides at-least-once delivery, so duplicates are possible. Making the Lambda function idempotent using a unique message deduplication ID (e.g., using the message ID as a condition in DynamoDB) prevents duplicates.
What should I do if I get this DVA-C02 question wrong?
Identify which DVA-C02 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Are there clue words in this question I should notice?
Yes — watch for: "least". You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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