Amazon SQS Long Polling not returning all messages

Question

I have a requirement to read all messages in my Amazon SQS queue in 1 read and then sort it based on created timestamp and do business logic on it.

To make sure all

Answer 1

As pointed out by Michael - sqlbot, SQS does not guarantee returning all (or the requested number of) messages even in case of Long Polling. Long Polling just ensures that you do not get false empty responses - i.e. your read requests do not return any messages even when there are messages in the queue.

I had done some experiments around this and found that the number of messages returned in the response approaches the number of the messages requested as you increase the number of messages in the queue. Typically, with 1000+ messages in the queue, in my experiments, I could see that it returned 10 messages (which is by the way the max that can be returned for a read request) everytime. In fact this behavior was observed for Short Polling as well. Even with 100+ messages, the number of messages returned was not 10 all the time, although a good percentage of those requests returned 10 messages back. Obviously, this is not guaranteed, but that is what you would typically see.

I had documented the findings from my experiments in one of my blogs - posting a link to the same below in case you would like to see more details of the experiment.

http://pragmaticnotes.com/2017/11/20/amazon-sqs-long-polling-versus-short-polling/