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From "Aaron T. Myers (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4523) Fix concat for snapshots
Date Tue, 26 Feb 2013 01:48:12 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4523?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13586608#comment-13586608
] 

Aaron T. Myers commented on HDFS-4523:
--------------------------------------

I'm not OK with committing something that makes the ostensibly immutable snapshots not in
fact immutable.

If you want to commit some interim solution until we can implement the proper semantics where
the source files are retained unmodified in the snapshot while the target is created in the
present file system, then I would be OK with changing concat to not allow any of the source
files to exist in any snapshots.
                
> 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_20130225b.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.

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