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From "Yufei Gu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-8828) Utilize Snapshot diff report to build copy list in distcp
Date Mon, 17 Aug 2015 16:27:46 GMT

    [ https://issues.apache.org/jira/browse/HDFS-8828?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14699781#comment-14699781
] 

Yufei Gu commented on HDFS-8828:
--------------------------------

Hi [~jingzhao],

Thank you very much for the review and nice comments! 

And thanks [~yzhangal] for good suggestions of comments 1 & 2. I agree that we need a
more reasonable place to carry information between different distcp stages if we don't use
the DistCpOptions. 

One of my thoughts is that we utilize a new class(or reuse the class DistCpSync) to carry
these information as [~yzhangal] suggested. Then add one object of the class as a member of
class SimpleCopyListing. This will avoid connecting Snapshot diff report with DistCpOptions,
but some function signatures should be changed, e.g. createInputFileListing, CopyListing#getCopyListing,
and so on. We also need to create a new class or add some members in class DistCpSync.

How do you guys think?

Thanks.

> Utilize Snapshot diff report to build copy list in distcp
> ---------------------------------------------------------
>
>                 Key: HDFS-8828
>                 URL: https://issues.apache.org/jira/browse/HDFS-8828
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: distcp, snapshots
>            Reporter: Yufei Gu
>            Assignee: Yufei Gu
>         Attachments: HDFS-8828.001.patch, HDFS-8828.002.patch, HDFS-8828.003.patch, HDFS-8828.004.patch,
HDFS-8828.005.patch, HDFS-8828.006.patch, HDFS-8828.007.patch
>
>
> Some users reported huge time cost to build file copy list in distcp. (30 hours for 1.6M
files). We can leverage snapshot diff report to build file copy list including files/dirs
which are changes only between two snapshots (or a snapshot and a normal dir). It speed up
the process in two folds: 1. less copy list building time. 2. less file copy MR jobs.
> HDFS snapshot diff report provide information about file/directory creation, deletion,
rename and modification between two snapshots or a snapshot and a normal directory. HDFS-7535
synchronize deletion and rename, then fallback to the default distcp. So it still relies on
default distcp to building complete list of files under the source dir. This patch only puts
creation and modification files into the copy list based on snapshot diff report. We can minimize
the number of files to copy. 



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