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https://issues.apache.org/jira/browse/HDFS-245?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12759595#action_12759595
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Doug Cutting commented on HDFS-245:
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> The FileContext API is not yet clearly baked as far as I can tell.
It's committed. It needs to get used. Adding the symlink feature there will
get both used and tested without altering existing codepaths.
> I'm fine with only doing it in file context... if we wait to checkin symlinks
> until FileSystem is fully deprecated.
I don't follow your logic here, Eric. Doesn't it make sense to first add a new
API in a trial manner? Pioneers can work out issues with symbolic links before
others are forced to move to the new API.
Symbolic links can be added to FileContext such a way that the only changes to
FileSystem would be to add a method, getLinkTarget(), that no existing code
calls. So the changes to Common are very low risk this way.
Separately we can then have a patch that adds symbolic link support to HDFS.
The primary change to existing codepaths here would be changing places where
FileNotFoundException would be thrown to instead throw UnresolvedLinkException
when the path to the file contains a symbolic link. The larger
risk/complication in HDFS is that links would be added to FileStatus, and hence
the namenode log format would need to be extended and we'd need a downgrade
story. So this patch would have more risk. But it can be considered
separately.
Additionally we can have patches that add support for local FS, S3, etc.
> Create symbolic links in HDFS
> -----------------------------
>
> Key: HDFS-245
> URL: https://issues.apache.org/jira/browse/HDFS-245
> Project: Hadoop HDFS
> Issue Type: New Feature
> Reporter: dhruba borthakur
> Assignee: dhruba borthakur
> Attachments: 4044_20081030spi.java, designdocv1.txt,
> HADOOP-4044-strawman.patch, symlink-0.20.0.patch, symLink1.patch,
> symLink1.patch, symLink11.patch, symLink12.patch, symLink13.patch,
> symLink14.patch, symLink15.txt, symLink15.txt, symlink16-common.patch,
> symlink16-hdfs.patch, symlink16-mr.patch, symlink17-common.txt,
> symlink17-hdfs.txt, symLink4.patch, symLink5.patch, symLink6.patch,
> symLink8.patch, symLink9.patch
>
>
> HDFS should support symbolic links. A symbolic link is a special type of file
> that contains a reference to another file or directory in the form of an
> absolute or relative path and that affects pathname resolution. Programs
> which read or write to files named by a symbolic link will behave as if
> operating directly on the target file. However, archiving utilities can
> handle symbolic links specially and manipulate them directly.
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