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From "Sanjay Radia (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4044) Create symbolic links in HDFS
Date Wed, 08 Oct 2008 03:03:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4044?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12637756#action_12637756

Sanjay Radia commented on HADOOP-4044:

Oops a few of my comments got deleted by mistake as I was doing cut/paste.


>My argument is that we should model normal functionality with normal programming: methods,
parameters, return values and data structures. Do you disagree with this? Or do you think
that links are not normal functionality?
>You keep arguing that "exceptions can be used for recoverable conditions". Indeed they
can. But is a link really best modeled as a "recoverable condition"? This sounds to me like
a rationalization for using exceptions, not a reason to use exceptions over data structures.

The way you have worded your questions makes it very hard for me to convey the alternative.
So I response in the best way I can (and you will not find the answer acceptable since I have
said some of this before).
I see following a symbolic link as an exceptional condition but not an error. The NN prefers
not to follow the remote symlinks.
It is however a condition that can be recovered by the client side.
Either the use of exceptions or data types and parameters are ways to deal with this.
I believe the use of exceptions in this situation is acceptable and further the better of
the two alternative.
Further I believe it leaves the methods signatures intact and they continue to convey the
function they previously did by their name and by the types of the in and out parameters.
I like that property of the solution. The alternate solution forces me to create a whole bunch
of new data types or overload existing one. If exceptions were not available I would use the
alternate solution.

I don't like  your use of term "normal control flow".That term was used in one of your references
for an example where and outOfBound exception was used to get out of a for loop at the array
index boundary. Clearly use of exceptions to exit out of a for loop for out of bounds is blasphemous.
So the issue is that  if I am forced to argue using the words normal or not normal it makes
my point of view ldiotic - the use of those words 
in that example do not apply in this context. 


> 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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