Each event message in Salesforce is assigned an opaque ID contained in the ReplayId field. The ReplayId field value, which is populated by the system refers to the position of the event in the event stream. Replay ID values are not guaranteed to be contiguous for consecutive events.

For example, the event following the event with Replay ID 999 can have Replay ID of 1,025. A subscriber can store a replay ID value and use it on re-subscription to retrieve events that are within the retention window.

For example, a subscriber can retrieve missed events after a connection failure. Subscribers must not compute new replay IDs based on a stored replay ID to refer to other events in the stream.