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From "Sanjay Radia (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4044) Create symbolic links in HDFS
Date Tue, 07 Oct 2008 18:18:46 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4044?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12637582#action_12637582
] 

Sanjay Radia commented on HADOOP-4044:
--------------------------------------

Dhruba says:
>If an exception is thrown by the ClientProtocol, it is logged by the RPC subsystem into
an error log. 
>This is a good characteristic to have in a distributed system, makes debugging easy because
a scan in the error logs
>pinpoints the exceptions raised by the API. 
>Access control checks or disk-full conditions raise exceptions, and they are logged by
the RPC subsystem. We do not want every call to "traverse a 
>symbolic link" to log an exception message in the error logs, do we? (Of course, we can
special case it and say that we will not log >UnresolvedPathException; but by
>special-casing it, we are acknowledging that this exception is not an abnormal behaviour).

The NN (or any server) should log server error (like disc full)   but not user exceptions
(like non-existent path name supplied).
The reason that access violation exceptions are logged is because it is needed for security
audits - security is a special case and the info may even be logged in a separate file.
Hence, in general,  the server side needs to filter what is logged.
If we has some inheritance hierarchy in our exceptions we could make the filter simpler.
The special casing argument is not valid since we should add some sort of a filter anyway
at some point.

> 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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