A. ShellBolt side control
We can modify ShellBolt to have sent tuple ids list, and stop sending tuples when list exceeds configured max value. In order to achieve this, subprocess should notify "tuple id is complete" to ShellBolt.
- It introduces new commands for multi-lang, "proceed" (or better name)
- ShellBolt stores in-progress-of-processing tuples list.
- Its overhead could be big, subprocess should always notify to ShellBolt when any tuples are processed.
B. subprocess side control
We can modify subprocess to check pending queue after reading tuple.
If it exceeds configured max value, subprocess can request "delay" to ShellBolt for slowing down.
When ShellBolt receives "delay", BoltWriterRunnable should stop polling pending queue and continue polling later.
How long ShellBolt wait for resending? Its unit would be "delay time" or "tuple count". I don't know which is better yet.
- It introduces new commands for multi-lang, "delay" (or better name)
- I don't think it would be introduced soon, but subprocess can request delay based on own statistics. (ex. pending tuple count * average tuple processed time for time unit, average pending tuple count for count unit)
- We can leave when and how much to request "delay" to user. User can make his/her own algorithm to control flooding.
In my opinion B seems to more natural cause current issue is by subprocess side so it would be better to let subprocess overcome it.