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From "Jing Zhao (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-8828) Utilize Snapshot diff report to build copy list in distcp
Date Mon, 03 Aug 2015 23:36:05 GMT

    [ https://issues.apache.org/jira/browse/HDFS-8828?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14652789#comment-14652789

Jing Zhao commented on HDFS-8828:

Thanks for the explanation, Yufei! Yes, you're right that our current code uses the file list
to check if a file is in the source. In that sense excluding "-delete" may be our only option
here. But we may need to provide more details in the documentation about the behavior, as
also suggested by Yongjun.

> 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
> 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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