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https://issues.apache.org/jira/browse/HDFS-8828?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14699950#comment-14699950
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Jing Zhao commented on HDFS-8828:
---------------------------------
Yes, we can try to use DistCpSync or a new class to carry the information. The
third way can be: handle diff related logic together, i.e., to have a separate
building list function for diff report based mechanism and call it immediately
after doing the sync. The code may look like:
{code}
if (use diff) {
get diff report
parse diff report
do sync based on rename/delete diff info
build copy list
} else {
all the original implementation
}
{code}
> 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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