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From "Bolke de Bruin (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (AIRFLOW-931) LocalExecutor fails to run queued task with race condition
Date Wed, 01 Mar 2017 22:09:45 GMT

    [ https://issues.apache.org/jira/browse/AIRFLOW-931?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15891162#comment-15891162
] 

Bolke de Bruin commented on AIRFLOW-931:
----------------------------------------

I don't think your analysis is correct. Line 1291 in models.py is only executed when "if not
runnable and not mark_success:". This means required dependencies are not met.

> LocalExecutor fails to run queued task with race condition
> ----------------------------------------------------------
>
>                 Key: AIRFLOW-931
>                 URL: https://issues.apache.org/jira/browse/AIRFLOW-931
>             Project: Apache Airflow
>          Issue Type: Bug
>    Affects Versions: Airflow 1.8, 1.8.0rc4
>            Reporter: Vijay Krishna Ramesh
>
> https://gist.github.com/vijaykramesh/707262c83429ab2a3f5ee701879813e3 provides a small
example that consistently hits this problem with LocalExecutor.
> Basically when the dag run kicks off (with concurrency > 1) and a LocalExecutor with
parallelism > 2 the scheduler marks more than concurrency tasks as queued (https://github.com/apache/incubator-airflow/blob/master/airflow/jobs.py#L1095)
> There is a second check before actually running the task (https://github.com/apache/incubator-airflow/blob/master/airflow/models.py#L1291)
that leaves the task in the QUEUED state but then the scheduler never picks it back up.  This
causes the DAG to get stuck (as the queued tasks never run) until the scheduler is restarted
(at which point the enqueued tasks are considered orphaned, the status is set to NONE, and
then they are picked up by the scheduler again and run.



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