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https://issues.apache.org/jira/browse/HDFS-3370?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13271450#comment-13271450
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M. C. Srivas commented on HDFS-3370:
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Creating hard-links in a distributed file-system will cause all kinds of future
problems with scalability. Hard-links are rarely used in the real-world,
because of all the associated bizzare problems. Eg, consider a hardlink setup
as follows:
link1: /path1/dirA/file
link2: /path2/dirB/file
1. Changing the permissions along the path "/path1/dirA" to make "file"
inaccessible works, but now with hard-links "/path2/dirB" is wide open.
2. Rename "/path2/dirB" to "/path3/dirC" will require taking locks on
"/path1/dirA" ... but the "file" does not have "parent ptrs" to figure out
which path(s) to lock.
I would recommend finding a different approach to implementing snapshots than
adding this feature.
> 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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