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https://issues.apache.org/jira/browse/MAPREDUCE-5211?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jason Lowe updated MAPREDUCE-5211:
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Resolution: Fixed
Fix Version/s: 0.23.8
Hadoop Flags: Reviewed
Status: Resolved (was: Patch Available)
Thanks for the reviews. I committed this to branch-0.23.
I do not believe the collision in branch-2/trunk is possible since it
concatenates an absolute path of a source file to a working directory specific
to the reduce attempt to build a destination path. The pathnames can become
very long, but I don't think they will collide. If we want to change that
behavior, we can handle it in another JIRA.
> Reducer intermediate files can collide during merge
> ---------------------------------------------------
>
> Key: MAPREDUCE-5211
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-5211
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: mrv2
> Affects Versions: 0.23.7
> Reporter: Jason Lowe
> Assignee: Jason Lowe
> Priority: Blocker
> Fix For: 0.23.8
>
> Attachments: MAPREDUCE-5211.branch-0.23.patch
>
>
> The OnDiskMerger.merge method constructs an output path that is not unique to
> a reduce attempt, and as a result can result in a file collision with other
> reducers from the same app that are running on the same node. In addition
> the name of the output file is based on MapOutput.toString which may not be
> unique in light of multi-pass merges on disk since the mapId will be null and
> the basename ends up as "MapOutput(null, DISK)"
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