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https://issues.apache.org/jira/browse/MAPREDUCE-7282?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17201046#comment-17201046
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Jim Brennan commented on MAPREDUCE-7282:
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I am -1 on the proposal to remove the v2 algorithm. Please see [~jlowe]'s
[comment|https://issues.apache.org/jira/browse/MAPREDUCE-4815?focusedCommentId=14271115&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14271115]
from the original discussion on [MAPREDUCE-4815].
We have been running with the v2 algorithm in production on large clusters for
years at Verizon Media (Yahoo). I don't think it is appropriate to remove it.
> MR v2 commit algorithm 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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