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From "Chris Douglas (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-11794) distcp can copy blocks in parallel
Date Thu, 23 Mar 2017 03:01:42 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-11794?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15937609#comment-15937609
] 

Chris Douglas commented on HADOOP-11794:
----------------------------------------

bq. the current patch would split a file and copy them into chunk files at target, then at
commit stage we will find concat doesn't work, thus the target is polluted (inconsistent state)

Doesn't this imply that FileSystems that support concat can also be left in an inconsistent
state? If the concat operation fails, the job is killed/fails/dies, etc. then distcp cleanup
should remove partial work. If a FileSystem doesn't support concat, shouldn't that failure
follow the same path?

Either way, +1 on the approach you outline. Thanks for considering the feedback and updating
the patch, [~yzhangal]. Looking forward to this enhancement; it's been a long time coming!

> distcp can copy blocks in parallel
> ----------------------------------
>
>                 Key: HADOOP-11794
>                 URL: https://issues.apache.org/jira/browse/HADOOP-11794
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: tools/distcp
>    Affects Versions: 0.21.0
>            Reporter: dhruba borthakur
>            Assignee: Yongjun Zhang
>         Attachments: HADOOP-11794.001.patch, HADOOP-11794.002.patch, HADOOP-11794.003.patch,
HADOOP-11794.004.patch, HADOOP-11794.005.patch, HADOOP-11794.006.patch, HADOOP-11794.007.patch,
HADOOP-11794.008.patch, MAPREDUCE-2257.patch
>
>
> The minimum unit of work for a distcp task is a file. We have files that are greater
than 1 TB with a block size of  1 GB. If we use distcp to copy these files, the tasks either
take a long long long time or finally fails. A better way for distcp would be to copy all
the source blocks in parallel, and then stich the blocks back to files at the destination
via the HDFS Concat API (HDFS-222)



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