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Date: Mon, 11 Jul 2016 18:00:12 +0000 (UTC)
From: "Arthur Wiedmer (JIRA)" <jira@apache.org>
To: commits@airflow.incubator.apache.org
Message-ID: <JIRA.12988340.1468253182000.81609.1468260012578@Atlassian.JIRA>
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Subject: [jira] [Commented] (AIRFLOW-323) Should be able to prevent tasks
 from overlapping across multiple DAG Runs
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archived-at: Mon, 11 Jul 2016 18:00:17 -0000


    [ https://issues.apache.org/jira/browse/AIRFLOW-323?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15371291#comment-15371291 ] 

Arthur Wiedmer commented on AIRFLOW-323:
----------------------------------------

Hi Isaac, it sounds like there are a couple of things that could help you :
1) You can set max_active_runs for the DAG to 1 to ensure that only one dag run is active at a time. In this case, only one dag run will be executed at a time.
2) You can set depend_on_past to True such that this task will not execute unless the previous one completes.
3) Finally, you can make this DAG use a pool with one slot, such that this task basically takes a lock on this particular resource.

Though ideally, if several tasks are competing for the same resource, you might not want to schedule them at a cadence that will introduce contention...

> Should be able to prevent tasks from overlapping across multiple DAG Runs
> -------------------------------------------------------------------------
>
>                 Key: AIRFLOW-323
>                 URL: https://issues.apache.org/jira/browse/AIRFLOW-323
>             Project: Apache Airflow
>          Issue Type: Bug
>    Affects Versions: Airflow 1.7.1.2
>         Environment: 1.7.1.2
>            Reporter: Isaac Steele
>            Assignee: Isaac Steele
>
> As a the Airflow administrator,
> If a task from a previous DAG Run is still running when the next scheduled run triggers the same task, there should be a way prevent the tasks from overlapping.
> Otherwise the same code could end up running multiple times simultaneously.
> To reproduce:
> 1) Create a DAG with a short scheduled interval
> 2) Create a task in that DAG to run longer than the interval
> Result: Both tasks end up running that the same time.
> This can cause tasks to compete for resources as well as duplicating or overwriting what the other task is doing.


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