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https://issues.apache.org/jira/browse/HDFS-3370?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13271453#comment-13271453
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Daryn Sharp commented on HDFS-3370:
-----------------------------------
I fully agree that posix and/or linux conventions should ideally be followed.
I did a little testing and didn't realize that a hard link retains the same
attrs (owner, group, perms, xattrs, etc) as the original file. Changing one
implicit changes the others, so that negates some issues such as differing
replication factor concerns. Perhaps hard link creation can be restricted to
only the file owner and superuser.
The quota concerns are still a bit more complex. Unixy systems like linux and
bsd only have fs level quotas for users, so quota handling is trivial compared
to directory level quotas in hdfs. Since all hard links implicitly have the
same owner, quotas are as simple as incrementing the user's ds quota is at file
creation, and decrement when all links are removed. This why a DOS is possible
against a user.
I'm sorry if I'm missing a detail, but I remain unclear on how you are
proposing to handle the directory level quotas. I don't fully grok how finding
a common ancestor with a quota is sufficient because quotas can be added or
removed at any time. Maybe part of the issue too is I have nested directories
with individual quotas in mind, whereas maybe you are assuming one and only one
quota from the root?
I look forward to your thoughts.
> 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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