[
https://issues.apache.org/jira/browse/HDFS-4523?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13586299#comment-13586299
]
Aaron T. Myers commented on HDFS-4523:
--------------------------------------
I really disagree with this premise. One of the main motivations of supporting
snapshots in HDFS is to allow the admin to roll back to the previous FS state
in the case of mistakes. Imagine for a moment that a large number of errant
concat operations are performed on source files which were in a snapshot. The
HDFS admin realizes this and then wants to restore the FS to its previous state
prior to the concat operations having been performed. The admin won't be able
to do so, however, because the concat operations will have removed the source
files from the snapshots. This is incongruous with the nature of all the other
FS operations, where an action taken in the present file system will have no
affect on the files in previously-created snapshots.
I realize that concat is a bit of an odd and little-used FS operation, but I
still see no reason that it should be treated fundamentally differently from
the other FS operations.
> Fix concat for snapshots
> ------------------------
>
> Key: HDFS-4523
> URL: https://issues.apache.org/jira/browse/HDFS-4523
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: namenode
> Reporter: Tsz Wo (Nicholas), SZE
> Assignee: Tsz Wo (Nicholas), SZE
> Attachments: h4523_20130222.patch, h4523_20130223.patch,
> h4523_20130225.patch
>
>
> The use case of concat is for copying large files across clusters using the
> following steps.
> - Step 1: The blocks of a file in the source cluster are copied in parallel
> to transient files in the destination cluster.
> - Step 2: Then the transient files in the destination cluster are
> concatenated in order to obtain the original file.
> If a snapshot is taken in the destination cluster before Step 2, some
> transient files may be captured in the snapshot. These transient files
> should be removed in Step 2.
--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira
