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https://issues.apache.org/jira/browse/HADOOP-4044?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12637534#action_12637534
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Doug Cutting commented on HADOOP-4044:
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Dhruba> the NameNode is not future-proof for backward compatibility.
Dhruba> Thus, exceptions could be used here. This keeps most of the HDFS code
clean and elegant.
Yes, they could be used here, and it could be fixed later without breaking user
code, but that doesn't make it clean and elegant. Rather it is a quick and
dirty hack. Returning normal values through exceptions is a perversion. The
Namenode should be revised to support links as first-class events, not as
exceptions.
Konstantin> This is universal, but not a transparent api anymore.
It's no less transparent than 'FileStatus getFileStatus(Path)'. In that case
we combined the value of many methods (isDirectory(), size(), owner(), etc.)
into the value of a single method with a very generic name.
In this case we wish to collapse three logical calls into one. We want to
perform 'isLink()',and then either 'getLink()' or, e.g., 'open()', and return
sufficient information so that the caller can tell what happened. In such
cases, when multiple values must be grouped together to represent something, we
use a data structure, not some other channel like exceptions or global
variables. With a data structure comes some loss of transparency, also called
abstraction.
> 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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