An orders service consumes payment instructions from an Amazon SQS queue. Sometimes the consumer times out after applying the payment but before deleting the SQS message. As a result, the same payment instruction is processed again. Which design change most directly prevents duplicate side effects caused by message retries?

Delete the SQS message immediately after it is received, before processing, to ensure it is not retried.

Deleting immediately breaks the at-least-once processing model. If processing fails after deletion (for example, before payment is committed), the message is lost and the side effect may not be applied correctly.

Increase the SQS visibility timeout to a maximum value to avoid retries entirely.

A larger visibility timeout reduces retry frequency but does not eliminate duplicates. If the consumer times out (or crashes) after applying the side effect and before deletion, the message will still be redelivered later, so duplicates can still occur.

Convert the queue to FIFO and enable content-based deduplication.

FIFO deduplication prevents duplicates based on message deduplication IDs at the time messages are sent to the queue. Message retries are redeliveries of the same enqueued message and are not prevented by content-based deduplication, so duplicate side effects are still possible without idempotent processing.

What does this SAA-C03 question test?

Read the scenario before looking for a memorised answer.

What is the correct answer to this question?

The correct answer is: Implement idempotency by recording a processed marker keyed by the instruction ID and ignoring duplicates. — SQS provides at-least-once delivery, so timeouts and crashes can cause the same message to be processed more than once. To prevent duplicate payment side effects, the system must be idempotent. Persist a processed marker keyed by the payment instruction ID (or enforce uniqueness in a database) so that if the same instruction is retried, the service recognizes it as already handled and does not apply the side effect again. Option A sacrifices reliability and can lose messages if processing fails after deletion. Option C only changes timing; it does not guarantee that duplicates never happen. Option D addresses enqueue-time duplicates, not retry-driven duplicate deliveries, so it does not replace idempotent side-effect handling.

What should I do if I get this SAA-C03 question wrong?

Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.