> I have two new questions: > > 1) the async operator must emit some value to the async collector > (even it acts as a sink), right? >
I think so, but you should be able to simply return empty collection. > 2) How could I use CheckpointListener with async operator? Could you > give a simple example or doc page? > There is an interface „CheckpointListener“ that your user function can implement that gives you a callback for completed checkpoints.
