Message Deduplication

5 minutes 5 Questions

Message Deduplication is the process of removing duplicate messages from an Amazon SQS FIFO queue, ensuring that each message is processed only once. To identify and remove duplicates, SQS uses a message deduplication ID, which is a unique value assigned to each message. This ID can either be expli…

Guide to Message Deduplication in Amazon SQS

Message Deduplication in Amazon Simple Queue Service (SQS) is an essential feature that prevents message duplication in a message queue. This guide explains its importance, function, and tips on answering exam questions related to this topic.

What is Message Deduplication?
In Amazon SQS, Message Deduplication identifies and removes duplicate messages. In FIFO (First In, First Out) queues, if a message with a particular deduplication ID is sent more than once within the five-minute deduplication interval, those messages are treated as duplicates and are discarded. This reduces unnecessary processing and helps ensure at-least-once processing in queues.

Why is it Important?
Message Deduplication ensures the processing of each specific message exactly once, eliminating the potential creation of replicated data or unforeseen server overload, and it is critical for maintaining accurate, reliable data streams.

How Does it Work?
Amazon SQS uses a default system-assigned deduplication ID (Sequence Number) or an optional user-defined deduplication ID. The former is unique for each message, whereas the latter is provided by the sender. This ID then helps Amazon SQS to detect and discard any duplicate messages.

Exam Tips: Answering Questions on Message Deduplication
1. Understand the process: Make sure you understand the deduplication process, from the assigning of the deduplication ID to the removal of duplicate messages.
2. Know the types of IDs: The exam may ask about the difference between system-assigned and user-defined deduplication IDs.
3. Application in FIFO Queues: Remember that Message Deduplication is only applicable in FIFO queues.
4. The deduplication interval: Keep in mind the deduplication interval during which Amazon SQS identifies duplicate messages, which is five minutes.

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Question 1

A company uses Amazon SQS with content-based message deduplication. An application occasionally resends a message when an error occurs. As the architect, how can you stop messages with the same content from being processed multiple times?

Disable message deduplication on the Amazon SQS queue. Configure a dead letter queue with a shorter retention period. Change the visibility timeout to a lower value. Enable message deduplication via message deduplication ID configured based on the message content.

Correct Answer: Enable message deduplication via message deduplication ID configured based on the message content.

By enabling message deduplication with a message deduplication ID based on the content, duplicate messages within a 5-minute deduplication window will be identified and removed. Disabling message deduplication, changing visibility timeout, configuring a dead letter queue, and switching to a FIFO queue are incorrect as they will not specifically address the issue of processing messages with the same content.

Question 2

How can you retrieve unprocessed messages after 24 hours from a high throughput Amazon SQS standard queue with message deduplication?

Increase the queue's message visibility timeout. Enable content-based deduplication using message deduplication ID. Use AWS Step Functions to consume messages from the queue. Create an SQS Dead Letter Queue and set the max receive count to a suitable value.

Correct Answer: Create an SQS Dead Letter Queue and set the max receive count to a suitable value.

Creating a Dead Letter Queue (DLQ) with an appropriate max receive count will store unprocessed messages up to 14 days. Increasing visibility timeout, enabling content-based deduplication, and using AWS Step Functions or Lambda functions don't directly affect the retrieval of unprocessed messages after 24 hours.

Question 3

Your client wants to ensure no duplicate messages are sent to their Amazon SQS FIFO queue. Which method can you use to enforce message deduplication?

Set the visibility timeout to a higher value. Assign the messages a unique message group ID. Generate a message deduplication ID based on message content. Enable Amazon S3 event notifications as a trigger to monitor duplicates.

Correct Answer: Generate a message deduplication ID based on message content.

Generating a message deduplication ID based on message content allows the FIFO queue to identify and remove duplicate messages. Changing visibility timeout, assigning a unique message group ID, enabling S3 event notifications, and adjusting the retention period don't directly address message deduplication.

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