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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4044) Create symbolic links in HDFS
Date Wed, 08 Oct 2008 16:37:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4044?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12637974#action_12637974
] 

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

Stepping back a bit, I don't believe this dispute is fundamentally about programming style.
 That, like Owen's arguments about RPCs, are supporting arguments.  The primary issue is that
we're changing the FileSystem API in a fundamental way.  Instead of direct functions that
map parameters to values, we wish to implement conditional functions, that do one of two things,
and indicate in their response which path was taken.  This is a very different style, one
that is forced on us for performance reasons.  The alternative is to double or more the number
of RPCs per file operation, which is unacceptable.

If we're using a different style, then it should look different.  It should not look like
the direct mapping of the existing API.  We should not attempt to hide this, as that will
lead to confusion.  We should make it apparent to readers of the code that these methods return
not a single type of value, but one of two kinds of values.  This is not a matter of exception
style, it's a matter of expressiveness and readability.  Code should make clear what it does.
 Style guidelines derive from this.  The reason exceptions are discouraged for normal control
flow is that they hide control flow.  We are factoring our FileSystem API in a different way,
and that factoring should be apparent to all as an obvious, natural attribute of the API.



> 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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