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https://issues.apache.org/jira/browse/HDFS-2006?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13997753#comment-13997753
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Andrew Wang commented on HDFS-2006:
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Related to limits, I also filed HDFS-6395 to enforce the # of xattrs per inode
limit differently based on namespace. This could be blown out to per-NS
settings, but I think it's sufficient to only enforce it for USER.
I'll also note that many existing FS have arbitrary limits on the size of an
xattr (e.g. page size) and that seems to work fine. I think it's unlikely we'd
need to support large xattrs either, especially since (as Nicholas points out)
we'd need to implement some special storage mechanism to avoid storing large
xattrs with the rest of the FS metadata. If anything, I expect per-NS configs
to be used to decrease the user limit.
Related to this, we might also want to enforce a hardcoded *minimum* limit for
the # and size of the non-user namespaces. This way, we could use xattrs for
system features even if the admin has configured wacky settings. Being able to
disable xattrs also makes it more annoying to rely on the system namespace,
maybe we should remove that config option as well. With per-NS limits, the
admin could still configure the user NS limits to 0 to prevent users from using
xattrs.
> 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: namenode
> Affects Versions: HDFS XAttrs (HDFS-2006)
> Reporter: dhruba borthakur
> Assignee: Yi Liu
> Attachments: ExtendedAttributes.html, HDFS-XAttrs-Design-1.pdf,
> HDFS-XAttrs-Design-2.pdf, HDFS-XAttrs-Design-3.pdf,
> Test-Plan-for-Extended-Attributes-1.pdf, xattrs.1.patch, xattrs.patch
>
>
> 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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