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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4044) Create symbolic links in HDFS
Date Fri, 26 Sep 2008 20:31:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4044?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12634998#action_12634998
] 

Doug Cutting commented on HADOOP-4044:
--------------------------------------

> Many return types are changed to return this path information.

Note that only the return types in the impl methods are changed.  The user methods retain
their original signatures.

> I think throwing the exception is enough [ ... ]

But a link is not an exceptional situation, it is a normal situation and should thus be handled
with normal control flow.  It does not require the non-local control flow that exceptions
provide.  The callee needs to pass specific information directly back to the caller.  Using
a common base class is appropriate here.

UnresolvedPathException is only used within HDFS, not in the FileSystem API.  My review has
focussed on the changes to the changes to the public FileSystem API, not to the HDFS implementation.
 Someone more familiar with HDFS should review the HDFS portiions of this patch.  On a cursory
examination, it does appear that this patch does use exceptions for control flow within HDFS,
which looks like a bad idea to me.  Rather HDFS's internal APIs should be modified to explicitly
handle links as return values.


> 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
>
>
> 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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