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https://issues.apache.org/jira/browse/HADOOP-13169?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15473384#comment-15473384
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Steve Loughran commented on HADOOP-13169:
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this is a good find.
# Have you run the hadoop-amazon and hadoop-azure distcp tests with this?
# Concurrency. You've marked {{statusList}} as a concurrent list, implying
there's concurrent use. But in {{writeToFileListing}} the list is shuffled,used
and then clear()-d in an unsynced block. Is there anything to stop elements
being added to the list between that shuffle/use and the clear() operation? as
that would lose entries in the distcp
> Randomize file list in SimpleCopyListing
> ----------------------------------------
>
> Key: HADOOP-13169
> URL: https://issues.apache.org/jira/browse/HADOOP-13169
> Project: Hadoop Common
> Issue Type: Improvement
> Components: tools/distcp
> Reporter: Rajesh Balamohan
> Priority: Minor
> Attachments: HADOOP-13169-branch-2-001.patch,
> HADOOP-13169-branch-2-002.patch, HADOOP-13169-branch-2-003.patch
>
>
> When copying files to S3, based on file listing some mappers can get into S3
> partition hotspots. This would be more visible, when data is copied from hive
> warehouse with lots of partitions (e.g date partitions). In such cases, some
> of the tasks would tend to be a lot more slower than others. It would be good
> to randomize the file paths which are written out in SimpleCopyListing to
> avoid this issue.
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