Simple Queue Service Concepts

This section describes the important concepts for the Simple Queue Service (SQS)

Queues and Queue URLs

A queue is a named destination for messages in an account. A queue has a URL that uniquely identifies it on the cloud.

Delivery and Visiblity

When a message is delivered to a client it is hidden from other clients for a period to prevent duplicate handling. If the message is not handled by the first client it will later become visible for handling by other clients.

Dead-letter Queues

A dead-letter queue can be used for undeliverable messages. Using a dead-letter queue allows for handling of messages that would otherwise not be processed.

Delay Queue

A delay queue allows messages to be available from a queue after a delay period rather than as soon as messages are sent to the queue.

Polling Style

Short or long polling can be used when receiving messages. For short polling there is an immediate response whether a message is available or not. For long polling a delay of up to 20 seconds is used and the response will occur when a message is available or when the given timeout is reached even if there is no message.