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From "Hila Visan (JIRA)" <j...@apache.org>
Subject [jira] [Created] (AIRFLOW-47) ExternalTaskSensor causes scheduling dead lock
Date Wed, 04 May 2016 06:41:12 GMT
Hila Visan created AIRFLOW-47:
---------------------------------

             Summary: ExternalTaskSensor causes scheduling dead lock
                 Key: AIRFLOW-47
                 URL: https://issues.apache.org/jira/browse/AIRFLOW-47
             Project: Apache Airflow
          Issue Type: Bug
          Components: operators, scheduler
    Affects Versions: Airflow 1.7.0
         Environment: CentOS 6.5
Airflow 1.7.0 with SequentialExecuter 
            Reporter: Hila Visan
            Priority: Trivial


We are trying to use 'ExternalTaskSensor' to coordinate between a daily DAG and an hourly
DAG  (daily dags  depend on hourly).
Relevant code: 

*Daily DAG definition:*
{code:title=2_daily_dag.py|borderStyle=solid}
default_args = {
    …
    'start_date': datetime(2016, 4, 2),
    …
}
dag = DAG(dag_id='2_daily_agg', default_args=default_args, schedule_interval="@daily")

ext_dep = ExternalTaskSensor(
    external_dag_id='1_hourly_agg',
    external_task_id='print_hourly1',
    task_id='evening_hours_sensor',
    dag=dag)
{code}

*Hourly DAG definition:*
{code:title=1_hourly_dag.py|borderStyle=solid}
default_args = {
    …
    'start_date': datetime(2016, 4, 1),
    …
}
dag = DAG(dag_id='1_hourly_agg', default_args=default_args, schedule_interval="@hourly")

t1 = BashOperator(
    task_id='print_hourly1',
    bash_command='echo hourly job1',
    dag=dag)
{code}

The hourly dag was executed twice for the following execution dates:
04-01T00:00:00	
04-01T01:00:00

Then the daily dag was executed, and is still running....	 
According to logs, daily dag is waiting for hourly dag to complete:
{noformat}
[2016-05-04 06:01:20,978] {models.py:1041} INFO - Executing<Task(ExternalTaskSensor): evening_hours_sensor>
on 2016-04-03 00:00:00
[2016-05-04 06:01:20,984] {sensors.py:188} INFO - Poking for 1_hourly_agg.print_hourly1 on
2016-04-02 00:00:00 ... 
[2016-05-04 06:02:21,053] {sensors.py:188} INFO - Poking for 1_hourly_agg.print_hourly1 on
2016-04-02 00:00:00 ... }}
{noformat}

How can I solve this dead-lock?

In Addition- I didn't understand if it means that the daily dag depends only on the "last"
hourly dag of the same day (23-24pm)? 
What happens if the hourly dag of other hour fails?

Thanks a lot! 







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