Long Polling

5 minutes 5 Questions

Long Polling is a feature of Amazon SQS that reduces the number of empty responses from a consumer querying an SQS queue for new messages. With Short Polling (default), consumers receive an immediate response, which might be empty if no messages are available. Long Polling, on the other hand, keeps the connection open for a specified time period (up to 20 seconds) while waiting for new messages. This reduces the number of empty responses and lowers the cost associated with API requests, providing a more efficient way for consumers to retrieve messages from an SQS queue.

AWS Solution Architect: A Guide to Amazon SQS Long Polling

In the context of AWS Solution Architect, Amazon's Simple Queue Service (SQS) and its long polling feature occupy an essential place.

What is Long Polling?
Long polling is a way to retrieve messages from your SQS queues. Unlike short polling, long polling doesn't return a response until a message arrives in the queue, or the long poll times out. Long polling helps to reduce the cost of using SQS by reducing the number of empty responses.

Why is it Important?
With Long Polling, empty responses are minimized, saving money and reducing unnecessary network traffic. It allows systems to retrieve messages as soon as they are available, providing better system responsiveness.

How it Works?
When you send a request to retrieve a message, if there are no messages immediately available, the long poll waits until a message arrives or the wait time for the long poll expires.

Exam Tips: Answering Questions on Long Polling
- Remember the key benefits of long polling i.e., cost-effective and reduced empty responses.
- Understand that long polling allows messages to be delivered as soon as they're available.
- Remember that you can set the wait time for long poll anywhere between 1 second to 20 seconds.
- Be aware that long polling is a feature only associated with SQS queues.

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Question 1

You have an application that highly relies on Amazon SQS. The consumers need to receive and process the messages quickly without increasing costs. Which polling method should you use?

Delayed Queue Long Polling Short Polling Visibility Timeout

Correct Answer: Long Polling

Long Polling allows the consumers to receive messages quickly and decreases costs, as it reduces empty responses and API action counts. Short Polling increases the chance of receiving empty responses. Visibility Timeout, delayed queues, message deduplication, or increasing the message size does not solve the requirement set by the question.

Question 2

Your company is running a large-scale, multi-AZ RDS instance that manages crucial data. To improve performance, they need to dispatch database events to application instances asynchronously. What Amazon Service and which feature can you implement for this task?

Amazon SNS with Long Polling Amazon SWF with Long Polling Amazon SQS with Long Polling Amazon SQS with Short Polling

Correct Answer: Amazon SQS with Long Polling

Amazon SQS provides a reliable and scalable queue service to handle asynchronous tasks along with Long Polling for efficient message retrieval. Amazon SNS is for pub/sub messaging and does not support long polling. Amazon SWF and AWS Step Functions support tasks, but not directly integrated with RDS. Short Polling does not provide performance required to answer this scenario.

Question 3

You are managing a high-volume application using SQS with a requirement to minimize empty responses from SQS API actions. What will you do?

Increase the visibility timeout Enable short polling Attach a Lambda function to the queue Enable Long Polling

Correct Answer: Enable Long Polling

Long Polling helps reducing empty responses by waiting up to 20 seconds for a message to be available, while short polling returns immediately with empty or non-empty results. Changing the visibility timeout, adding Lambda functions, enabling message deduplication, or increasing concurrency level will not directly affect the problem of empty responses.

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