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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 00:49:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4044?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12637331#action_12637331

Sanjay Radia commented on HADOOP-4044:

Doug says:
>> [minor]  the method next() suggests that one follows the path to the next symbolic
link. It does not strictly.

>Can you elaborate? Each time this is called a link is resolved, returning a path that
may contain more links, following a chain of links, no? Also, >'doOperation()' is next
to meaningless. So if 'next' is indeed inappropriate we should replace it with something more
specific, not something generic.

First I had qualified this as _minor_ (meaning it is just a minor suggestion for the author).
When I read the code, I first thought that dhruba was  processing all sym links and then doing
the actual operation at the end.
Turns out next() actually performs the operation. If the operation succeeds (and it will for
most pathnames including for all dot-relative symlinks)
all is well and done. Indeed if there is another NN in a chain of links that is willing to
process remote  symlinks internally all is fine and done.
If the operations  fails, then the recovery is performed.
Now the design is quite elegant. Later we can add new reasons why the NN could not complete
the operation and the structure could be modified
to recover for new conditions. I like that. The name next() suggests that one is following
 symlinks so I was suggesting something like doOperaiton() or
performOperation() which I find more accurate than the the generic "next()". 
Perhaps adding a comment to the abstract method may be sufficient. _I am okay with whatever
the author decides here - it is a very minor comment_.

> 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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