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From "Devaraj Das (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-1985) Abstract node to switch mapping into a topology service class used by namenode and jobtracker
Date Fri, 14 Dec 2007 12:27:43 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-1985?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Devaraj Das updated HADOOP-1985:

    Attachment: 1985.v1.patch

Attached is a tested patch. The patch has better documentation too. One of the important changes
in the patch to do with testcases is the way it handles multiple datanodes in the same machine.
Since the namenode should be able to distinguish between them in terms of the dnsToRackId
mapping, I added a configuration option called "slave.host.name" that would take effect only
when the framework is run under junit. Ditto applies to the jobtracker/tasktrackers. Also
all communications to these dummy hostnames are redirected to "localhost" (indirectly via

Patch is up for review.

> 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
>          Issue Type: New Feature
>            Reporter: eric baldeschwieler
>            Assignee: Devaraj Das
>         Attachments: 1985.new.patch, 1985.v1.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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