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From "dhruba borthakur (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 Thu, 07 Feb 2008 21:31:08 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1985?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12566806#action_12566806
] 

dhruba borthakur commented on HADOOP-1985:
------------------------------------------

I like sanjay's proposal. If the namenode receives a block report but the datanode's hostname
has not been resolved yet, then the NN sets a bit in the DatanodeDescriptor that indicates
that the namenode should request a block report. The NN then dumps the contents of this block
report on the floor but returns success to the block-report RPC. 

Finally, when the name of the datanode is resolved and if this new bit is set, then the NN
sends a request-for-block-report request as part of the response to a heartbeat from that
datanode.

> 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.v2.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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