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https://issues.apache.org/jira/browse/HDFS-12544?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16211876#comment-16211876
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Manoj Govindassamy commented on HDFS-12544:
-------------------------------------------

Thanks for the review comments [~yzhangal]. Good discussion on the file rename 
behavior w.r.t snapshot diff for descendant directory. Thats right, the renamed 
files still show up in the diff report as "R" entry even though they are moved 
out of the scope (descendant) directory. To get the same behavior as the normal 
snapshot diff report, these renamed files whose target is not under the scoped 
directory should be shown as "D" deleted entries in the report. Will post a new 
patch to handle this case.

> SnapshotDiff - support diff generation on any snapshot root descendant 
> directory
> --------------------------------------------------------------------------------
>
>                 Key: HDFS-12544
>                 URL: https://issues.apache.org/jira/browse/HDFS-12544
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs
>    Affects Versions: 3.0.0-beta1
>            Reporter: Manoj Govindassamy
>            Assignee: Manoj Govindassamy
>         Attachments: HDFS-12544.01.patch, HDFS-12544.02.patch, 
> HDFS-12544.03.patch
>
>
> {noformat}
> # hdfs snapshotDiff <snapshot_root_path> <from_snapshot_name> 
> <to_snapshot_name>
> {noformat}
> Using snapshot diff command, we can generate a diff report between any two 
> given snapshots under a snapshot root directory. The command today only 
> accepts the path that is a snapshot root. There are many deployments where 
> the snapshot root is configured at the higher level directory but the diff 
> report needed is only for a specific directory under the snapshot root. In 
> these cases, the diff report can be filtered for changes pertaining to the 
> directory we are interested in. But when the snapshot root directory is very 
> huge, the snapshot diff report generation can take minutes even if we are 
> interested to know the changes only in a small directory. So, it would be 
> highly performant if the diff report calculation can be limited to only the 
> interesting sub-directory of the snapshot root instead of the whole snapshot 
> root.



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