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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2006) ability to support storing extended attributes per file
Date Fri, 27 May 2011 18:01:48 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2006?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13040357#comment-13040357
] 

dhruba borthakur commented on HDFS-2006:
----------------------------------------

@Konstantin: This feature can be used in a very generic fashion to store file attributes:
one can build ACL style permissions, per-file-block-placement-policies, etc.etc.

@Aaron: The block-to-file ratio is not big, so we need to manage memory usage on the namenode
very carefully.

@Matt: It would be fine for the clients to do another disk access to read the extended attributes.
The overall thinking I have in mind is somewhat like this: the NN stores the location of the
extended attribute. This location can znode-identifier or a generic URL, let's call it the
attributeURL. The HDFS-client makes a call to the NN to fetch the attributeURL and then directly
accesses the attribute contents. If we limit the length of the attributeURL, then the NN can
possibly cache it in memory.



> ability to support storing extended attributes per file
> -------------------------------------------------------
>
>                 Key: HDFS-2006
>                 URL: https://issues.apache.org/jira/browse/HDFS-2006
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: name-node
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>
> It would be nice if HDFS provides a feature to store extended attributes for files, similar
to the one described here: http://en.wikipedia.org/wiki/Extended_file_attributes. 
> The challenge is that it has to be done in such a way that a site not using this feature
does not waste precious memory resources in the namenode.

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