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From "Konstantin Shvachko (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4044) Create symbolic links in HDFS
Date Sat, 11 Oct 2008 00:33:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4044?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12638694#action_12638694
] 

Konstantin Shvachko commented on HADOOP-4044:
---------------------------------------------

Doug> Does that address your question?

Yes it does in the way that I see you are changing the subject.
It was about exception usage, now it is about monolithic layers of HDFS.
Since the programming style correctness is not measurable as opposed to performance there
is no definite answer on what is correct/incorrect, and therefore the discussion clearly can
go on forever. If one argument is exhausted another can be raised or linked to the previous,
and so on.

Although the question you raise is interesting by itself.
HDFS is not a single monolithic layer the same way as Hadoop is not a single layer. MapReduce
as a layer on top of HDFS but we do not impose the knowledge of splits upon the file system.
Going further up the stack we also do not require HDFS to recognize HBase records or files
corresponding to columns in a table store.

HDFS layers are clearly different abstractions. E.g., NameNode does not know about input and
output streams. Sure, the layers have common structures, say FileStatus is visible to all
layers, but ContentSummary is constructed on the top FileSystem level.

I don't think this argument works in favor of your approach and justifies passing link values
through the whole hierarchy of HDFS layers.

> 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: HADOOP-4044-strawman.patch, 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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