The Notification Stream operator takes a relation as input, and outputs a stream that consists of events whose presence is determined by a specified time interval.
Assume that the following conditions are true:
If the event is still in the relation at 2:01 in the afternoon, then the event is included in the output stream for the first time.
If the event is still in the relation at 2:02 in the afternoon, then the event is included in the output stream for the second time.
If the event is still in the relation at 2:03 in the afternoon, then the event is included in the output stream for the third time.
If the event is no longer in the relation at 2:04 in the afternoon, then the event is no longer included in the output stream.
The scenario in Using the Gap Window Operator involves creating a relation that indicates which message is missing at any point in time. You could use the Notification Stream operator to create an output stream of resend requests for the missing messages. Connect the Gap Window operator to a Notification Stream operator, configure the time interval, and then send the output to a Stream Output operator.
To use the Notification Stream operator: