StreamingGraphExecutor.is_task_ready(...)	Return true if pending task is ready
StreamingGraphExecutor.poll_tasks(...)	Wait for any change in status to pending_task_list
StreamingGraphExecutor.split_batch_submit(...)	Submit a task to split batch into at most max_rows
StreamingGraphExecutor.task_resolve_output(...)	Return a StreamBatch from completed task
StreamingGraphExecutor.task_submit(task, df_list)	Run or arrange for the running of task
StreamingGraphExecutor.task_submittable(...)	Preflight check if task can be submitted