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