[jira] [Commented] (AIRFLOW-4881) Zombie collection fails task instances that should be scheduled for retry

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/AIRFLOW-4881?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16877151#comment-16877151 ] 

ASF GitHub Bot commented on AIRFLOW-4881:
-----------------------------------------

tamasflamich commented on pull request #5514: [AIRFLOW-4881] Persist the max_tries field of task instances during zombie collection
URL: https://github.com/apache/airflow/pull/5514
 
 
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   ### Jira
   
   - [ ] My PR addresses the following [Airflow Jira](https://issues.apache.org/jira/browse/AIRFLOW-4881) issues and references them in the PR title.
     - https://issues.apache.org/jira/browse/AIRFLOW-4881
   
   ### Description
   
   - [ ] Here are some details about my PR, including screenshots of any UI changes:
   
   In case a task instance
   - has more attempts than retries (it can happen when the state of the task instance is explicitly cleared) and
   - task instance is prematurely terminated (without graceful shutdown)
   then zombie collection process of the scheduler can mark the task instance failed instead of up_for_retry.
   
   This happens because the `max_retries` field is not persisted but set to its initial value (`retries`). 
   
   ### Tests
   
   - [ ] My PR adds the following unit tests __OR__ does not need testing for this extremely good reason:
   
   ### Commits
   
   - [ ] My commits all reference Jira issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "[How to write a good git commit message](http://chris.beams.io/posts/git-commit/)":
     1. Subject is separated from body by a blank line
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     1. Body explains "what" and "why", not "how"
   
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     - All the public functions and the classes in the PR contain docstrings that explain what it does
     - If you implement backwards incompatible changes, please leave a note in the [Updating.md](https://github.com/apache/airflow/blob/master/UPDATING.md) so we can assign it to a appropriate release
   
   ### Code Quality
   
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> Zombie collection fails task instances that should be scheduled for retry
> -------------------------------------------------------------------------
>
>                 Key: AIRFLOW-4881
>                 URL: https://issues.apache.org/jira/browse/AIRFLOW-4881
>             Project: Apache Airflow
>          Issue Type: Bug
>          Components: scheduler
>    Affects Versions: 1.10.3
>            Reporter: Tamas Flamich
>            Priority: Major
>
> In case a task instance
>  * has more attempts than retries (it can happen when the state of the task instance is explicitly cleared) and
>  * task instance is prematurely terminated (without graceful shutdown)
> then zombie collection process of the scheduler can mark the task instance failed instead of retrying it. 
> Steps to reproduce:
> 1 - The task is scheduled for a particular executed date and the following records gets created in the database.
> ||task_id||retries||try_number||max_tries||state||
> |emr_sensor|2|1|2|running|
> 2 - The job owners would like to schedule the task again therefore they clear that state of the task instance. {{try_number}} and {{max_retries}} gets updated.
> ||task_id||retries||try_number||max_tries||state||
> |emr_sensor|2|2|3|running|
> 3 - The Airlflow scheduler gets killed and a new scheduler instance starts looking for zombie tasks. Since {{try_number < max_tries}}, the new state is {{up_for_retry}}. However, there is a bug in the [state update logic|https://github.com/apache/airflow/blob/d5a5b9d9f1f1efb67ffed4d8e6ef3e0a06467bed/airflow/models/dagbag.py#L295] that will revert the {{max_tries}} value to the initial value ({{retries}}).
> ||task_id||retries||try_number||max_tries||state||
> |emr_sensor|2|2|2|up_for_retry|
> 4 - During the next iteration of the scheduler, the task instance gets picked up. However, since {{try_number >= max_tries}}, the new state is {{failed}}.
> ||task_id||retries||try_number||max_tries||state||
> |emr_sensor|2|2|2|failed|



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