[jira] [Commented] (AIRFLOW-764) max_active_runs_per_dag not respected for DAGs triggered manually within a few seconds of one another

["Alexander Panzhin (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/AIRFLOW-764?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15851975#comment-15851975 ] 

Alexander Panzhin commented on AIRFLOW-764:
-------------------------------------------

This is a major problem when migrating to Airfllow. It's impossible to backfill manually DAGs and not manage them manually - what's the point of a workflow management tool then?

> max_active_runs_per_dag not respected for DAGs triggered manually within a few seconds of one another
> -----------------------------------------------------------------------------------------------------
>
>                 Key: AIRFLOW-764
>                 URL: https://issues.apache.org/jira/browse/AIRFLOW-764
>             Project: Apache Airflow
>          Issue Type: Bug
>          Components: core, executor
>    Affects Versions: Airflow 1.7.1.3
>         Environment: debian linux, mysql with localexecutor
>            Reporter: Jeffrey Enns
>         Attachments: test_dag.py, test_dag_screen.png, test_job.sh, trigger_two.sh
>
>
> Given the following configuration:
> ```
> [core]
> executor = LocalExecutor
> max_active_runs_per_dag = 1
> parallelism = 20
> dag_concurrency = 1
> ```
> Even with `max_active_runs_per_dag=1`, it is possible to cause two (or more) DAG runs to run in parallel by triggering the runs manually within a few seconds/milliseconds of one another. Task Instances from the distinct DAG runs will show as active in the “Task Instances” web view at the same time.
> I only looked at the scheduler code briefly, but it looked as if a race condition would be possible for manually triggered DAGs that could lead to this behaviour.
> I’ve attached a test DAG and two shell scripts I used to reliably reproduce this behaviour. Put `test_dag.py` and `test_job.sh` in the DAGs folder, and then run `trigger_two.sh` to reproduce the bug. 
> Also attached is a screenshot showing DAG runs (for the dag ‘race_dag’) running in parallel after following the steps described immediately above (note the execution date, start date, and end date for each TI).



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