An example of a non-idempotent operation is to increase a counter by one, where the operation will have additional side effects every time it’s applied.

By using idempotent operations, we can have the guarantee that even if a node delivers a message multiple times and repeats the operation, the result will be the same.

However, idempotent operations commonly impose tight constraints on the system. So, in many cases, we cannot build our system so that all operations are idempotent by nature. In these cases, we can use another approach: the de-duplication approach.