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https://issues.apache.org/jira/browse/HDFS-3370?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13294229#comment-13294229
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Konstantin Shvachko commented on HDFS-3370:
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> I would recommend finding a different approach to implementing snapshots than
> adding this feature.
I agree with Srivas, hard links seem easy in single-NameNode architecture, but
they are very hard to support when the namespace is distributed, because if
links to a file belong to different nodes you cannot just lock the entire
namespace and do atomic cross-node linking / unlinking.
I also agree with Srivas that hard links in traditional file systems cause more
problems than add value.
Looking at the design document I see that you create sort of internal symlinks
called INodeHardLinkFile pointing to HardLinkFileInfo, representing the actual
file. This can be modeled by symlinks on the application (HBase) level without
making any changes in HDFS.
I strongly discourage bringing this feature inside HDFS.
Or provide use cases which *cannot* be solved without it.
> 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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