[jira] [Resolved] (MAPREDUCE-4831) Task commit can occur more than once due to AM retries

["Jason Lowe (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/MAPREDUCE-4831?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Jason Lowe resolved MAPREDUCE-4831.
-----------------------------------

    Resolution: Not A Problem

After discussing this at length with Bobby, we came to the conclusion that this isn't a problem.  Task commit can already occur multiple times due to things like fetch failure, etc.  The OutputCommitter is responsible for guarding against task double-commit if that indeed is a problem.
                
> Task commit can occur more than once due to AM retries
> ------------------------------------------------------
>
>                 Key: MAPREDUCE-4831
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-4831
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: mr-am
>    Affects Versions: 0.23.0, 2.0.0-alpha
>            Reporter: Jason Lowe
>            Priority: Critical
>
> If a task attempt begins committing but the AM crashes before the task attempt completes then we could end up having the task commit again when the AM is relaunched.  The subsequent AM attempt will not see the task having completed, so it will re-run the task and it will commit again.  The output committer is user code, and the task commit may not be something repeatable.  Therefore we should treat an AM crash during a task attempt commit the same as we do for a commit failure by the task attempt, i.e.: the task should fail since we do not know how to recover from a commit failure.
> This is similar to MAPREDUCE-4819, as this involves commit at the task level and that involves commit at the job-level.

--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira