We have seen exceptions from workers
The stack trace points to LoadAwareShuffleGrouping.java#L234:
This is because in some situation,
the above code will be 0 during the whole for-loop. For example, when there are more than 1000 (which is CAPACITY) downstream tasks, say 1001, and each task has weight 1. Then for every target task, count =(int) ( (1 / 1001.0) * 1000) = 0.