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https://issues.apache.org/jira/browse/AIRFLOW-764?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15925004#comment-15925004
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Bolke de Bruin commented on AIRFLOW-764:
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please verify with 1.8.0 (rc5)
> 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: Screen Shot 2017-02-03 at 7.53.06 PM.png, 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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