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https://issues.apache.org/jira/browse/HADOOP-8470?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13291539#comment-13291539
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Junping Du commented on HADOOP-8470:
------------------------------------

Hi Luke, That's a reasonable concern. Thanks for noting this out. Do you think 
I can leave the terminology naming work to you and other committers? I will 
keep terminology as "NodeGroup" here as consistent with other patches, but will 
update all terminologies once you have made decision. What's the correct way to 
gather everyone's idea on this? Is that filing a JIRA or send email to 
common-dev?
Yes. I also have a dream that topology of hadoop can be flexible enough with 
optimised reliability and performance in any environment with easy 
configuration from user. I believe that day is not far. :)

Cheers,

Junping 

                
> Implementation of 4-layer subclass of NetworkTopology 
> (NetworkTopologyWithNodeGroup)
> ------------------------------------------------------------------------------------
>
>                 Key: HADOOP-8470
>                 URL: https://issues.apache.org/jira/browse/HADOOP-8470
>             Project: Hadoop Common
>          Issue Type: Sub-task
>    Affects Versions: 1.0.0, 2.0.0-alpha
>            Reporter: Junping Du
>            Assignee: Junping Du
>         Attachments: HADOOP-8470-NetworkTopology-new-impl-v2.patch, 
> HADOOP-8470-NetworkTopology-new-impl-v3.patch, 
> HADOOP-8470-NetworkTopology-new-impl.patch
>
>
> To support the four-layer hierarchical topology shown in attached figure as a 
> subclass of NetworkTopology, NetworkTopologyWithNodeGroup was developed along 
> with unit tests. NetworkTopologyWithNodeGroup overriding the methods add, 
> remove, and pseudoSortByDistance were the most relevant to support the 
> four-layer topology. The method seudoSortByDistance selects the nodes to use 
> for reading data and sorts the nodes in sequence of node-local, 
> nodegroup-local, rack- local, rack–off. Another slightly change to 
> seudoSortByDistance is to support cases of separation data node and node 
> manager: if the reader cannot be found in NetworkTopology tree (formed by 
> data nodes only), then it will try to sort according to reader's sibling node 
> in the tree.
> The distance calculation changes the weights from 0 (local), 2 (rack- local), 
> 4 (rack-off) to: 0 (local), 2 (nodegroup-local), 4 (rack-local), 6 (rack-off).
> The additional node group layer should be specified in the topology script or 
> table mapping, e.g. input 10.1.1.1, output: /rack1/nodegroup1
> A subclass on InnerNode, InnerNodeWithNodeGroup, was also needed to support 
> NetworkTopologyWithNodeGroup.

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