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From "Joydeep Sen Sarma (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4044) Create symbolic links in HDFS
Date Thu, 11 Sep 2008 18:31:45 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4044?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12630292#action_12630292

Joydeep Sen Sarma commented on HADOOP-4044:

wrt Allen's comment - i think it's not without merit. he's probably thinking about moving
things within the same hdfs instance - in which case having to have a symlink per leaf is
going to lead to doubling of inodes (for the subtree being moved).

Couple of orthogonal ideas:
1. would it not be easy to write a new file system client that does component by component
lookup? (instead of DFSClient behavior). this would not seem to require any namenode changes.
2. support symlinks only within the same hdfs instance. the namenode can resolve things internally
- no changes to the client.

then we can combine these two approaches. The namenode can return specific error if it finds
the path to be resolved has reference to external fs (using work done in #2). The regular
DFSClient can revert to special client file system that does component by component lookup
(work done in #1) in case of this error. this will prevent having to incur the overhead of
component by component lookup unless one hits a symlink that crosses fs boundary.

> 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
> 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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