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From "Aaron T. Myers (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4523) Fix concat for snapshots
Date Mon, 25 Feb 2013 20:14:16 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4523?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13586246#comment-13586246
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Aaron T. Myers commented on HDFS-4523:
--------------------------------------

Hi Nicholas, unless I'm misunderstanding something, I think I question the premise of this
JIRA. Judging by the description, it sounds like you're saying that when a concat(...) is
performed on a set of files after those files have been included in a snapshot, that that
snapshot should be modified to include the final concat'ed file, instead of the constituent
files pre-concat. That would seem to violate the "read-only" premise of snapshots, which doesn't
seem like the correct behavior to me.

Please let me know if I misunderstood the intent of this JIRA.

Thanks.
                
> 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
>
>
> 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.

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