Very good blog to read about the life cycle of messages in SQS,a%20large%20number%20of%20messages.&text=There%20is%20no%20concept%20of,visibility%20timeout%20provided%20by%20SQS.

Important points:

  1. Delivery of Messages can be delayed
  2. Messages have an expiry
  3. Dead letter queues if unable to process a message. Unable to process is identified by number of retries to read a message.
  4. Once a message is being read by a consumer, this message shouldn’t be processed by another service at the same time. So when a message is being read, you can configure SQS so that same message wont be read by multiple consumers. This concept is called as Visibility Timeout.

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