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From "Tsz Wo (Nicholas), SZE (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4044) Create symbolic links in HDFS
Date Fri, 10 Oct 2008 01:12:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4044?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12638460#action_12638460
] 

Tsz Wo (Nicholas), SZE commented on HADOOP-4044:
------------------------------------------------

> It seems like the only motivation to call this an error is to justify using exceptions
to handle links, not that it would in fact be a user or program error to call it in this way.

It is nothing wrong to assume parameter f a non-linked path.  For performance reason, clients
are responsible to resolve links before using it since resolving links is expensive, especially
for cross-file-system links.

Suppose we have the following link
  hdfs://clusterA/project/xxx ->  hdfs://clusterB/yyy

If a client submit a job with hdfs://clusterA/project/xxx/input and hdfs://clusterA/project/xxx/output,
all the input and output file accesses involve two clusters and require two calls.  However,
if the client uses hdfs://clusterB/yyy, only one cluster is involved.

> 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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