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From "Hila Visan (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (AIRFLOW-47) ExternalTaskSensor causes scheduling dead lock
Date Wed, 04 May 2016 07:07:13 GMT

    [ https://issues.apache.org/jira/browse/AIRFLOW-47?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15270213#comment-15270213
] 

Hila Visan commented on AIRFLOW-47:
-----------------------------------

I just figured out that if the _'start_date'_ parameter of both of the dags is the same (1/4/16
in my example) - it works!

So I assume that the best practice for dag dependency is to use the same _'start_date'_ if
all my dags are new,
Or - If I add a new dag to the system- make sure that all dependencies of the new dag have
been already met.

> 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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