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From "Yongjun Zhang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-11794) distcp can copy blocks in parallel
Date Wed, 09 Dec 2015 04:40:11 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-11794?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15048017#comment-15048017
] 

Yongjun Zhang commented on HADOOP-11794:
----------------------------------------

Thanks [~mithun] and [~dhruba]!  

There will be some complexity with regard to block size since we now support variable size
block (introduced by the append feature). We might need ask NN for the size of all blocks
a file has, and avoid have the split boundary at the middle of a block. Another possibility
is, to split the block into two if it happens (since now we support multiple size block),
I have not looked deeper at this yet.

And I'm thinking we could have one FileSplit per multiple file-blocks, we can make it as an
input option to distcp.

Thanks again.


> 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: 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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