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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4044) Create symbolic links in HDFS
Date Fri, 10 Oct 2008 18:45:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4044?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12638625#action_12638625

Doug Cutting commented on HADOOP-4044:

Konstantin> checked exceptions can be used when a particular layer does not have an immediate
response to the condition causing the exception

First, in this case, I consider HDFS to be a single layer, or module.  HDFS controls all of
its components.  The calls on the stack above that are still part of HDFS are known to HDFS,
are under HDFS's control and are modified in a coordinated manner, as a unit.  In particular,
all of HDFS knows that a link can be to an external FileSystem, since this is a generic property
of all FileSystems.  This is a safe assumption for any code in HDFS to make, and does not
violate any abstraction boundaries within HDFS.

An exception is justified when the best handler for it is unknown.  It is not the immediacy
of the handler, or the proximity of the handler, but whether the handler is fully determined.
 If the handler is known, then exceptions are just being used as a convenient message passing
channel.  When the destination is known, methods, parameters and return values are the preferred
message passing mechanisms in object-oriented programming.

Does that address your question?

> 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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