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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 20:46:13 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4523?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13586263#comment-13586263
] 

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

bq. That's not correct. The final concat'ed file won't be in the previously created snapshots.
Only the transient files are removed.

Gotcha. Thanks for the clarification.

Still, though, I think the point remains - the supposedly read-only snapshot which was created
when those source files were in the FS will be modified to remove those source files which
were concat'ed. That doesn't seem correct to me. Why shouldn't the snapshot continue to have
those source files?
                
> 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.

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