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https://issues.apache.org/jira/browse/MAPREDUCE-4815?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14102509#comment-14102509
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Siqi Li commented on MAPREDUCE-4815:
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Ming, you are right. When restarting the cluster for upgrade. It might run into
some problems with old output structure.
Does it have to throw some exceptions in this case? Originally, it just gives
some warnings.
> FileOutputCommitter.commitJob can be very slow for jobs with many output files
> ------------------------------------------------------------------------------
>
> Key: MAPREDUCE-4815
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-4815
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: mrv2
> Affects Versions: 0.23.3, 2.0.1-alpha, 2.4.1
> Reporter: Jason Lowe
> Assignee: Siqi Li
> Attachments: MAPREDUCE-4815.v3.patch
>
>
> If a job generates many files to commit then the commitJob method call at the
> end of the job can take minutes. This is a performance regression from 1.x,
> as 1.x had the tasks commit directly to the final output directory as they
> were completing and commitJob had very little to do. The commit work was
> processed in parallel and overlapped the processing of outstanding tasks. In
> 0.23/2.x, the commit is single-threaded and waits until all tasks have
> completed before commencing.
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