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Date: Sat, 2 Jun 2012 13:05:23 +0000 (UTC)
From: "Lars Hofhansl (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
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Subject: [jira] [Commented] (HDFS-3370) HDFS hardlink
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    [ https://issues.apache.org/jira/browse/HDFS-3370?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13287931#comment-13287931 ] 

Lars Hofhansl commented on HDFS-3370:
-------------------------------------

@M.C. Srivas: Isn't that the same for any file?
A rename of a file renames one of its references. I don't understand how the fact that the file has more references has any impact on that.

Hardlinks are incredibly useful for applications like HBase, where an immutable HFile could just be mapped to another directory (not just for backup purposes).

                
> HDFS hardlink
> -------------
>
>                 Key: HDFS-3370
>                 URL: https://issues.apache.org/jira/browse/HDFS-3370
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>            Reporter: Hairong Kuang
>            Assignee: Liyin Tang
>         Attachments: HDFS-HardLink.pdf
>
>
> We'd like to add a new feature hardlink to HDFS that allows harlinked files to share data without copying. Currently we will support hardlinking only closed files, but it could be extended to unclosed files as well.
> Among many potential use cases of the feature, the following two are primarily used in facebook:
> 1. This provides a lightweight way for applications like hbase to create a snapshot;
> 2. This also allows an application like Hive to move a table to a different directory without breaking current running hive queries.

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