At least once processing
The at least once processing paradigm involves a mechanism to save the position of the last event received only after the event is actually processed and results persisted somewhere so that, if there is a failure and the consumer restarts, the consumer will read the old events again and process them. However, since there is no guarantee that the received events were not processed at all or partially processed, this causes a potential duplication of events as they are fetched again. This results in the behavior that events ate processed at least once.
At least once is ideally suitable for any application that involves updating some instantaneous ticker or gauge to show current values. Any cumulative sum, counter, or ...
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