I found that often we want to be able to ensure that certain part of some topic was processed before starting doing joins with that topic.

For example we join stream A with table B. We know a point in time where topic B would be mostly read. It may not be completely recovered, because messages are constantly coming in. But we know that we need at least the portion before that point in time to be available for joins.

So the idea would be to wait until certain processing time of topic B before starting processing topic A.

I could assume that using processor’s stats something like this could be achieved, but I’m not sure.

I’ve tried sleeping in A’s callback until particular record of topic B is available, but found out that topic B is stalling when topic A sleeps.