- If the backend guarantees order, the messages are received in the precise order in which they were sent. For example, if message
M1was sent before
M2, you will not receive
M2first and then
- If the backend does not guarantee order, you very well may receive
If backend is a multi-tenant distributed system, order preservation may require extra effort and cause performance penalty. That is why, say, SQS provides this property as an optional feature for extra pay.