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https://issues.apache.org/jira/browse/MAPREDUCE-650?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12728485#action_12728485
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Ravi Gummadi commented on MAPREDUCE-650:
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Since with -update, after copying files to stagedir, moving from stagedir to
actual destinationDir cannot be atomic. So am planning to change the patch to
support -atomic <stageDir> option only without -update. If both options are
used together, distcp would give error message and exits.
> Add atomic move option
> ----------------------
>
> Key: MAPREDUCE-650
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-650
> Project: Hadoop Map/Reduce
> Issue Type: New Feature
> Components: distcp
> Reporter: Richard Theige
> Assignee: Ravi Gummadi
> Attachments: d_retries_atomic.patch, d_retries_atomic_v1.patch
>
>
> Provide support for update to move directories/files atomically by copying
> the src directory to a tmp directory (with random/unique name) then move the
> directory to its target destination name after all subdirs/files are copied
> and verified.
> example option ideas
> hadoop ... distcp -update -move src dst
> or
> hadoop ... distcp -update -atomic src dst
> to assure file correctness at the destination, before distcp performs the
> 'move' at the end of the copy process, it should first perform a strong
> signature/cksum (e.g. MD4) on the files.
> The issue/need for this is that applications may attempt to start processing
> data (because files are present), prior to completion of a whole directory
> copy -- resulting in work against an incomplete data set.
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