Meaning – The term idempotency refers to the property of a mathematical operation whereby repeating the operation produces no change in the final result. For example, the operation of deducting $25.00 from an account balance is not idempotent, but the operation of setting an account balance to $500.00 is idempotent.
It also refers to a property that enables the sender of a request to repeat the request with a guarantee that the outcome will be the same regardless of whether the request is lost, the response is lost, or the request or response is delayed due to network problems. Idempotency is necessary because the SET protocol works in environments where message delivery is not guaranteed, and when the sender does not receive a response, it cannot determine the cause of the delay.
Example of usage – “When the receiving SET application determines that it has already processed that message, it retrieves the previous response and sends that response again.”