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From "Hairong Kuang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3370) HDFS hardlink
Date Fri, 04 May 2012 21:51:48 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3370?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13268735#comment-13268735
] 

Hairong Kuang commented on HDFS-3370:
-------------------------------------

Sajay, you are right. HDFS hardlink is only a meta operation and no datanode is involved.
In all our use cases, the source file may be deleted over time but its content can be still
accessed through hardlinks.
                
> 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-HardLinks.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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