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https://issues.apache.org/jira/browse/MAPREDUCE-7282?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17198317#comment-17198317
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Steve Loughran commented on MAPREDUCE-7282:
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Proposed
* we change the default
* documents to say dangerous because ...
* jobs run with v2 start with a warn "deprecated will be removed"
That's for all shipping 3.x releases. Then for trunk we downgrade to v1, always
(or better, cut all the co-recursive complexity of the committer)
> MR v2 commit algorithm is dangerous, should be deprecated and not the default
> -----------------------------------------------------------------------------
>
> Key: MAPREDUCE-7282
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-7282
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: mrv2
> Affects Versions: 3.3.0, 3.2.1, 3.1.3, 3.3.1
> Reporter: Steve Loughran
> Priority: Major
>
> The v2 MR commit algorithm moves files from the task attempt dir into the
> dest dir on task commit -one by one
> It is therefore not atomic
> # if a task commit fails partway through and another task attempt commits
> -unless exactly the same filenames are used, output of the first attempt may
> be included in the final result
> # if a worker partitions partway through task commit, and then continues
> after another attempt has committed, it may partially overwrite the output
> -even when the filenames are the same
> Both MR and spark assume that task commits are atomic. Either they need to
> consider that this is not the case, we add a way to probe for a committer
> supporting atomic task commit, and the engines both add handling for task
> commit failures (probably fail job)
> Better: we remove this as the default, maybe also warn when it is being used
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