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https://issues.apache.org/jira/browse/HDFS-8828?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14699664#comment-14699664
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Yongjun Zhang commented on HDFS-8828:
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Hi [~jingzhao],
Thanks for the review and good comments!
Some thoughts:
Currently {{DistCpOptions}} is currently the only vehicle to pass info between
different stages of distcp. To address your comment 1 & 2, we need to add
something new to pass additional info (which is derived data, and can be hold
by a new class) to pass between sync and copyListing stages. To do this, there
are two choices:
1. Pass an object of this new class as a standalone parameter between stages,
which require changing quite some method signatures, most of the places don't
use this new parameter.
2. Put the object of this class as a member of DistCpOptions, so there is no
need to change method signatures. We can create another new class
{{DistCpDerivedInput}} to hold derived input, and put all derived data as
members of {{DistCpDerivedInput}}. If we define DistCpOptions as only holding
command line options, then then this choice is not perfect; however, if we
define DistcpOptions as may-contain derived input too, then it's ok.
Which choice you like better? or additional thoughts?
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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