This DEA-C01 practice question tests your understanding of data store management. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 data engineering team is building a real-time analytics pipeline using Amazon Kinesis Data Streams, AWS Lambda, and Amazon DynamoDB. The Lambda function consumes records from the stream and writes aggregated data to a DynamoDB table. The application requires that each record be processed exactly once to avoid duplicates. The Lambda function is idempotent, but occasionally duplicate records are written due to retries from Kinesis. The team needs to ensure exactly-once semantics for DynamoDB writes. Which solution should they implement?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use DynamoDB TransactWriteItems with a condition check on a unique transaction ID.
Option B is correct because DynamoDB TransactWriteItems with a condition check on a unique transaction ID ensures that the write only succeeds if the transaction ID does not already exist in the table. This provides exactly-once semantics by preventing duplicate writes even when Kinesis retries deliver the same record multiple times. The condition check acts as a distributed lock at the item level, guaranteeing idempotency without relying on downstream deduplication.
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.
✗
Enable DynamoDB Streams and use a second Lambda to deduplicate.
Why it's wrong here
Introduces complexity and eventual consistency.
✓
Use DynamoDB TransactWriteItems with a condition check on a unique transaction ID.
Why this is correct
Condition check ensures only one write succeeds per unique ID.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use the Kinesis Client Library (KCL) to checkpoint after processing and ignore duplicates.
Why it's wrong here
Checkpointing does not prevent duplicates from being written.
✗
Ensure the Lambda function is idempotent by using upsert operations.
Why it's wrong here
Idempotency alone may not prevent duplicates if multiple writes are attempted.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume idempotent Lambda functions alone guarantee exactly-once processing, but they overlook that Kinesis retries can still cause duplicate writes unless a conditional write with a unique identifier is used at the database level.
Detailed technical explanation
How to think about this question
Under the hood, DynamoDB TransactWriteItems uses a client-side token (idempotency token) to ensure that the same transaction is not applied more than once, even if the request is retried. The condition expression on a unique transaction ID (e.g., 'attribute_not_exists(transactionId)') leverages DynamoDB's conditional writes, which are atomic and serializable. In a real-world scenario, this pattern is critical for financial transactions or inventory systems where duplicate writes could lead to double-counting or inconsistent state.
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 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 exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Data Store Management — This question tests Data Store Management — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use DynamoDB TransactWriteItems with a condition check on a unique transaction ID. — Option B is correct because DynamoDB TransactWriteItems with a condition check on a unique transaction ID ensures that the write only succeeds if the transaction ID does not already exist in the table. This provides exactly-once semantics by preventing duplicate writes even when Kinesis retries deliver the same record multiple times. The condition check acts as a distributed lock at the item level, guaranteeing idempotency without relying on downstream deduplication.
What should I do if I get this DEA-C01 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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Question Discussion
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