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https://issues.apache.org/jira/browse/HADOOP-4044?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12629575#action_12629575
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Doug Cutting commented on HADOOP-4044:
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Right, we should optimize dot-relative and volume-root-relative links so that
they're resolved with a single RPC.
In all cases, with HDFS links into the same filesystem, we should make just a
single RPC to its namenode on open. We used to have an open() RPC, but that
was replaced with getBlockLocations() when we noticed that open was no
different than getBlockLocations(). With symlinks, we should probably add an
open() call again.
Open() could return a struct with 3 fields: isLink, linkTarget and
blockLocations. Dot-relative and volume-root-relative links can be resolved on
the NN, as follows:
||file type|isLink|linkTarget|blockLocations||
|regular|false|null|non-null|
|dot relative link|true|resolved path|non-null|
|volume-root relative link|true|resolved path|non-null|
|link to other filesys|true|foreign path|null|
Does that make sense?
> 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
>
>
> 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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