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https://issues.apache.org/jira/browse/MAPREDUCE-5211?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13652425#comment-13652425
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Siddharth Seth commented on MAPREDUCE-5211:
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Jason, the 0.23 patch looks ok. Maybe we should add a utility method to
generate intermediate output file names.
I think a variant of this does exist in trunk as well. The OnDiskMerger it's
first inputPath as the outputPath - which means it could end up overwriting
this file in a multi-stage merge ?
> 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: Critical
> 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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