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From "Jing Zhao (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-4167) Add support for restoring/rolling back to a snapshot
Date Fri, 25 Apr 2014 07:06:17 GMT

     [ https://issues.apache.org/jira/browse/HDFS-4167?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Jing Zhao updated HDFS-4167:

    Attachment: HDFS-4167.000.patch

Here is a very initial patch that only provides NameNode side functionalities. In general,
this patch provides a restoreSnapshot call in FSNamesystem, which restores a file/directory
to the most recent snapshot of the corresponding snapshottable directory. In particular, the
patch tries to do the following:
1. For a directory, revert its metadata change, restore deleted children and delete newly
created files/subdirs.
2. For a file, revert its metadata change, delete blocks that were created after the snapshot.
3. For a renamed file/dir, if the target of the rename operation is also under the restore
root directory, rename the file/dir back. Otherwise keep tracking the renamed file/dir in
the deleted list of the snapshot diff.
4. Update quota correspondingly.

Note that the snapshot must be the most recent one. We throw exceptions if there are intermediate
snapshot. This is the same behavior with ZFS.

Remaining work:
1. Unit tests and bug fixes.
2. Protocol change and FileSystem API.
3. CLI support
4. We also need to figure out how to handle the last block when the snapshot was taken. Do
we want to truncate the block to make the restored file's length consistent with the length
recorded in snapshot? But because of the current snapshot's copy-on-write semantic, the recorded
file length is also not accurate. We can only guarantee that the file length recorded in the
snapshot is no less than the real file length at the time when the snapshot was taken.

> Add support for restoring/rolling back to a snapshot
> ----------------------------------------------------
>                 Key: HDFS-4167
>                 URL: https://issues.apache.org/jira/browse/HDFS-4167
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: namenode
>    Affects Versions: Snapshot (HDFS-2802)
>            Reporter: Suresh Srinivas
>            Assignee: Jing Zhao
>         Attachments: HDFS Design Proposal.pdf, HDFS-4167.000.patch
> This jira tracks work related to restoring a directory/file to a snapshot.

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