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From "Devaraj Das (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1985) Abstract node to switch mapping into a topology service class used by namenode and jobtracker
Date Fri, 22 Feb 2008 12:24:19 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1985?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12571375#action_12571375
] 

Devaraj Das commented on HADOOP-1985:
-------------------------------------

Yes, this is really an INCOMPATIBLE change. If this is indeed a concern, then what you suggest
to do with keeping "-r" option makes sense. My worry is that we will end up having two ways
of resolving things in the framework since the MapReduce side of things will use the new approach.
The other issue is this that the separation of deprecated and new code won't be that distinct
(as in the case of deprecation of an API where we invoke the new method implementation inside
the deprecated method) since the patch touches a bunch of files at the level of implementation
of methods. But if deprecation is a real concern, I will address it.

> Abstract node to switch mapping into a topology service class used by namenode and jobtracker
> ---------------------------------------------------------------------------------------------
>
>                 Key: HADOOP-1985
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1985
>             Project: Hadoop Core
>          Issue Type: New Feature
>          Components: dfs, mapred
>            Reporter: eric baldeschwieler
>            Assignee: Devaraj Das
>             Fix For: 0.17.0
>
>         Attachments: 1985.new.patch, 1985.v1.patch, 1985.v10.patch, 1985.v11.patch, 1985.v19.patch,
1985.v2.patch, 1985.v20.patch, 1985.v3.patch, 1985.v4.patch, 1985.v5.patch, 1985.v6.patch,
1985.v9.patch, jobinprogress.patch
>
>
> In order to implement switch locality in MapReduce, we need to have switch location in
both the namenode and job tracker.  Currently the namenode asks the data nodes for this info
and they run a local script to answer this question.  In our environment and others that I
know of there is no reason to push this to each node.  It is easier to maintain a centralized
script that maps node DNS names to switch strings.
> I propose that we build a new class that caches known DNS name to switch mappings and
invokes a loadable class or a configurable system call to resolve unknown DNS to switch mappings.
 We can then add this to the namenode to support the current block to switch mapping needs
and simplify the data nodes.  We can also add this same callout to the job tracker and then
implement rack locality logic there without needing to chane the filesystem API or the split
planning API.
> Not only is this the least intrusive path to building racklocal MR I can ID, it is also
future compatible to future infrastructures that may derive topology on the fly, etc, etc...

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