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https://issues.apache.org/jira/browse/MAPREDUCE-6854?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17802820#comment-17802820
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Shilun Fan commented on MAPREDUCE-6854:
---------------------------------------
Bulk update: moved all 3.4.0 non-blocker issues, please move back if it is a
blocker. Retarget 3.5.0.
> Each map task should create a unique temporary name that includes an object
> name
> --------------------------------------------------------------------------------
>
> Key: MAPREDUCE-6854
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-6854
> Project: Hadoop Map/Reduce
> Issue Type: Improvement
> Components: distcp
> Affects Versions: 3.0.0-alpha2
> Reporter: Gil Vernik
> Priority: Major
> Labels: patch
> Attachments: HADOOP-6854-001.patch, HADOOP-6854-002.patch
>
>
> Consider an example: a local file "/data/a.txt" need to be copied into
> swift://container.service/data/a.txt
> The way distcp works is that first it will upload "/data/a.txt" into
> swift://container.mil01/data/.distcp.tmp.attempt_local2036034928_0001_m_000000_0
> Upon completion distcp will move
> swift://container.mil01/data/.distcp.tmp.attempt_local2036034928_0001_m_000000_0
> into swift://container.mil01/data/a.txt
> ************************************
> The temporary file naming convention assumes that each map task will
> sequentially create objects as swift://container.mil01/.distcp.tmp.attempt_ID
> and then rename them to the final names. Most of Hadoop eco system
> components use object.name which is part of the temporary name, however
> distcp doesn't use such approach.
> This JIRA propose to add a configuration key indicating that temporary
> objects will also include object name as part of their temporary file name,
> For example
> "/data/a.txt" will be uploaded into
> "swift://container.mil01/data/a.txt.distcp.tmp.attempt_local2036034928_0001_m_000000_0"
> "a.txt.distcp.tmp.attempt_local2036034928_0001_m_000000_0" doesn't affects
> flows in the access drivers, since "a.txt" is not considered as a
> sub-directory so no special operations will be taken.
> The benefits of the patch :
> 1. Temp object names will be better distributed in object stores, since they
> all has different prefix.
> 2. Sometimes it's not possible to debug what data is copied and what failed.
> Sometimes temp files are not renamed, it will be much better if expecting
> temp name - one can figure what object names were copied.
> 3. Different systems may expect
> "a.txt.distcp.tmp.attempt_local2036034928_0001_m_000000_0" and extract value
> prior "distcp.tmp" thus getting destination object name.
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