feng-tao commented on a change in pull request #3688: [AIRFLOW-2843]
ExternalTaskSensor-check if external task exists
URL: https://github.com/apache/incubator-airflow/pull/3688#discussion_r207604878
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File path: airflow/sensors/external_task_sensor.py
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@@ -70,9 +76,24 @@ def __init__(self,
self.execution_date_fn = execution_date_fn
self.external_dag_id = external_dag_id
self.external_task_id = external_task_id
+ self.check_existence = check_existence
@provide_session
def poke(self, context, session=None):
+ TI = TaskInstance
+
+ if self.check_existence:
+ existence = session.query(TI).filter(
+ TI.dag_id == self.external_dag_id,
+ TI.task_id == self.external_task_id,
+ ).count()
+ session.commit()
+ if existence == 0:
+ raise AirflowException('The external task "' +
Review comment:
why stop waiting if the external task not exist? Shouldn't the right
behavior to continue waiting for the task until task exist and finish(or
timeout?). Sometimes the external task may not start right on time(e.g
scheduler reason etc) and we still want downstream task wait for external task
to finish first to make sure result align.
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