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From "Andy Isaacson (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3370) HDFS hardlink
Date Tue, 03 Jul 2012 20:32:38 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3370?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13406011#comment-13406011
] 

Andy Isaacson commented on HDFS-3370:
-------------------------------------

{quote}
you keep the data along with the file (including the current file owner), you could do it
all from a library.
{quote}
The fundamental problem with "do it in a client library" is, there are always clients who
do not or cannot use the library.  Then the symlinks don't work for those clients.  I think
it's pretty clear that "open(2) transparently folows symlinks unless you ask it not to" is
a superior developer experience to "open the file, is it a .LNK? then follow the link else
return".  Even if there's a helper implementing the latter.
                
> 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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