理想情况下的状态流转
none =》scheduled =》 queued =》 running =》 success.
task实例状态含义
none: The Task has not yet been queued for execution (its dependencies are not yet met)
scheduled: The scheduler has determined the Task’s dependencies are met and it should run。 当running和queued的任务数量过大时，后续产生的任务实例都会处于scheduled状态。每次scheduler调度任务时，选出次状态的任务执行。
queued: The task has been assigned to an Executor and is awaiting a worker。scheduler将task传给executor，放入执行队列
running: The task is running on a worker (or on a local/synchronous executor)。任务task运行中
success: The task finished running without errors。任务task执行成功
shutdown: The task was externally requested to shut down when it was running
restarting: The task was externally requested to restart when it was running
failed: The task had an error during execution and failed to run。任务task执行失败
skipped: The task was skipped due to branching, LatestOnly, or similar. 某个分支中存在跳过某个任务的情况
upstream_failed: An upstream task failed and the Trigger Rule says we needed it。 依赖的上游任务失败后，下游的任务都被标记为failed
up_for_retry: The task failed, but has retry attempts left and will be rescheduled. 任务失败但尚未按照配置的重试次数进行重试
up_for_reschedule: The task is a Sensor that is in reschedule mode。等待任务再次被调度
sensing: The task is a Smart Sensor
deferred: The task has been deferred to a trigger
removed: The task has vanished from the DAG since the run started