DVA-C02 Troubleshooting and Optimization Practice Question

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 to ensure messages are deleted before becoming visible again.

  Why this is correct

  A message in SQS is hidden from other consumers the moment it is received, but only for the duration of the visibility timeout. If your processing time exceeds this window, the message becomes visible again and can be picked up by another consumer, causing the same message to be processed twice. Increasing the visibility timeout gives the original consumer enough time to finish processing and call DeleteMessage, so the message is removed before it can ever be redelivered.

• ✗

  Configure a dead-letter queue to capture duplicates.

  Why it's wrong here

  A dead-letter queue (DLQ) is not designed to deduplicate messages; it exists to quarantine messages that repeatedly fail to be processed after a configured number of receive attempts. Duplicate processing happens when a message becomes visible again after its visibility timeout expires, and a DLQ has no mechanism to prevent that redelivery. It simply stores those problematic messages for later analysis, but it does not stop the underlying duplicate from being consumed.

• ✗

  Increase the delivery delay to defer message processing.

  Why it's wrong here

  The delivery delay feature, also known as delay queues, postpones the first time a message becomes available to consumers by a set number of seconds. Once that initial delay elapses and the message is delivered, the delay has no further impact on how SQS handles that message. It does not extend the visibility timeout, so a message can still be redelivered and processed twice if the consumer takes too long to delete it.

• ✗

  Enable long polling to reduce empty responses.

  Why it's wrong here

  Long polling is a technique that reduces the number of empty ReceiveMessage responses by holding the connection open until a message arrives or the poll interval expires. This saves API calls and lowers cost, but it does not change SQS's at-least-once delivery guarantee. Even with long polling enabled, a standard queue can still deliver the same message more than once when the visibility timeout is too short, so long polling is irrelevant to the duplicate-processing problem.

• ✓

  Use a FIFO queue with content-based deduplication.

  Why this is correct

  FIFO queues provide exactly-once processing by design, which eliminates the duplicate delivery issue inherent to standard SQS queues. With content-based deduplication, SQS uses a SHA-256 hash of the message body to detect and discard duplicate messages sent within a 5-minute deduplication interval, ensuring each message is delivered and processed exactly once. This directly addresses the root cause of duplicate processing, unlike visibility timeout tuning which only reduces the likelihood.