Snapshot

PI Snapshot Subsystem gets the new data from the interface node and holds the most recent value for each point. This most recently acquired value for a point is called the snapshot.

Data Archive evaluates the previous snapshot according to the compression specifications and either sends the old value to the event queue or discards it.

Note: Sometimes an event enters PI Snapshot Subsystem with a time stamp that is older than the current snapshot value. This is called an out-of-order event. Data Archive sends out-of-order events directly to the event queue for archiving, without compression testing.

These values in PI Snapshot Subsystem are called snapshot events or just snapshots. The collection of all the snapshot values for all the points is the Snapshot Table.

Note: The out-of-order event is the incoming event with the older timestamp of the last event in the system.