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https://issues.apache.org/jira/browse/AIRFLOW-5391?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Qian Yu reassigned AIRFLOW-5391:
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Assignee: Qian Yu
> Clearing a task skipped by BranchPythonOperator will cause the task to execute
> ------------------------------------------------------------------------------
>
> Key: AIRFLOW-5391
> URL: https://issues.apache.org/jira/browse/AIRFLOW-5391
> Project: Apache Airflow
> Issue Type: Bug
> Components: operators
> Affects Versions: 1.10.4
> Reporter: Qian Yu
> Assignee: Qian Yu
> Priority: Major
>
> I tried this on 1.10.3 and 1.10.4, both have this issue:
> E.g. in this example from the doc, branch_a executed, branch_false was
> skipped because of branching condition. However if someone Clear
> branch_false, it'll cause branch_false to execute.
> !https://airflow.apache.org/_images/branch_good.png!
> This behaviour is understandable given how BranchPythonOperator is
> implemented. BranchPythonOperator does not store its decision anywhere. It
> skips its own downstream tasks in the branch at runtime. So there's currently
> no way for branch_false to know it should be skipped without rerunning the
> branching task.
> This is obviously counter-intuitive from the user's perspective. In this
> example, users would not expect branch_false to execute when they clear it
> because the branching task should have skipped it.
> There are a few ways to improve this:
> Option 1): Make downstream tasks skipped by BranchPythonOperator not
> clearable without also clearing the upstream BranchPythonOperator. In this
> example, if someone clears branch_false without clearing branching, the Clear
> action should just fail with an error telling the user he needs to clear the
> branching task as well.
> Option 2): Make BranchPythonOperator store the result of its skip condition
> somewhere. Make downstream tasks check for this stored decision and skip
> themselves if they should have been skipped by the condition. This probably
> means the decision of BranchPythonOperator needs to be stored in the db.
>
> [kevcampb|https://blog.diffractive.io/author/kevcampb/] attempted a
> workaround and on this blog. And he acknowledged his workaround is not
> perfect and a better permanent fix is needed:
> [https://blog.diffractive.io/2018/08/07/replacement-shortcircuitoperator-for-airflow/]
>
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