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https://issues.apache.org/jira/browse/MAPREDUCE-7500?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Rob Reeves updated MAPREDUCE-7500:
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Attachment: flamegraph_commit.png
> Support optimistic file renames in the commit protocol
> ------------------------------------------------------
>
> Key: MAPREDUCE-7500
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-7500
> Project: Hadoop Map/Reduce
> Issue Type: Improvement
> Components: client
> Reporter: Rob Reeves
> Priority: Minor
> Attachments: flamegraph_commit.png
>
>
> During a file commit in FileOutputCommitter, it assumes a file may be in the
> destination location and if so will delete it first. This means for every
> file commit is calls FileSystem.getFileStatus for the destination. For the
> Spark use case, there will be nothing existing in the destination location
> for the expected case so the getFileStatus call is wasted in all, but
> exceptional and unexpected cases.
> The getFileStatus call can take significant time. When I profiled a commit in
> our environment (HDFS, intermittent latency issues) the
> FileSystem.getFilestatus call takes 50% of the commit time. We have an
> aggressive auto-msync setting, but even when I disabled msync I saw the same
> behavior. I attached an example flame graph for the commit time.
> To avoid the time spent on getFileStatus, there should be an option to
> optimistically commit the file assuming there will be no conflict in the
> destination.
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