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From "Konstantin Shvachko (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4044) Create symbolic links in HDFS
Date Thu, 09 Oct 2008 19:38:46 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4044?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12638367#action_12638367
] 

Konstantin Shvachko commented on HADOOP-4044:
---------------------------------------------

I understand your answer to my question [HADOOP-4044#action_12638156] is that
_this argument is about the programming style_
rather than performance or anything else. Or do you call differently?

Qouting one of the links you provide 
"Checked exceptions : represent invalid conditions in areas outside the immediate control
of the program"

If a program cannot cannot handle some condition it throws a checked exception.
So the question of whether the value of a link is normal data is actually program layer-dependent.
- Can it be handled within the name-node. Yes for local links - handle them. No for external
links. Throw the exception.
- Can it be handled by ClientProtocol. No. Throw the exception.
- Can it be handled by DFSClient. No. Throw the exception.
- Can it be handled by DistributedFileSystem. No. Throw the exception.
- Can it be handled by FileSystem. Yes! because FileSystem cashes file system implementations.

FileSystem is the first layer for which link  values make sense.


> Create symbolic links in HDFS
> -----------------------------
>
>                 Key: HADOOP-4044
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4044
>             Project: Hadoop Core
>          Issue Type: New Feature
>          Components: dfs
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>         Attachments: symLink1.patch, symLink1.patch, 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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