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https://issues.apache.org/jira/browse/HDFS-12544?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16211833#comment-16211833
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Yongjun Zhang commented on HDFS-12544:
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Hi [~manojg],
One thought, about snapshotDiff to scoped dir, if we have a move operation "mv
x y", where x is in the scoped dir, and y is not in scoped dir, but both are in
snapshot root hierarchy. There are two issues:
# If we do snapshotDiff on snapshot root, we will get a "rename" operation,
this helps distcp to do a "sync" without copying renamed file. With the change
of this jira, we will lose the optimization. If the different sub-dirs are very
independent, then we are fine. We can document this though.
# With this change, it's expected that we get a "delete" entry when doing
snapshotDiff at the source dir and "new" entry when doing snapshotDiff at the
target dir. Would you please confirm if this is the case?
# If the result of 2 is not as expected, we need to have new patch rev to fix
it.
Thanks.
> 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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