In a JOIN task, I understand that the frequency of the “leftmost” upstream determines the frequency of the output stream.
How does it determine which one is the leftmost stream? Can this be explicitly controlled by the developer?
In the below example, it seems that WindStream is the leftmost one.
In the documentation I found the following discussion on this subject:
“An important note about joins is the order of the upstream tasks matters. The leftmost stream above the join determines the maximum frequency with which joins can be made. The output from a join task is unique for each unique event from the leftmost parent task. If the leftmost parent of the join produces events once every 10 seconds, the join will emit events at most once every 10 seconds, regardless of the frequency of the other parent tasks.”