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https://issues.apache.org/jira/browse/MAPREDUCE-4815?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13505479#comment-13505479
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eric baldeschwieler commented on MAPREDUCE-4815:
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Bikas:
Anyone who wants to use S3 as a target is going to have trouble w this. Of
course, that is the case w the MR1 implementation too, so this is not a
regression. But we're going to need to put energy into providing an
alternative approach that does work w cloud stores at some point. It would be
great if a solution emerged here that did not involve moving of files. That
would reduce the burden on the HDFS meta-data system too, which would be a good
thing for scalability.
> 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
> Reporter: Jason Lowe
> Assignee: Arun C Murthy
>
> 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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