[jira] [Commented] (HADOOP-8928) Add ability to reset topologies on master nodes

["Steve Loughran (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-8928?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13476058#comment-13476058 ] 

Steve Loughran commented on HADOOP-8928:
----------------------------------------

I do think this is good idea -we've discussed it before- I'm linking it up with HADOOP-8231;

* It should go into the HADOOP-7777 abstract switch mapping class with a recursive reset operation that will stop at the first non-resettable topology mapping. 
* It also needs a remote way to reset the mappings, which is an extension of HADOOP-8232, as a topology reset command would have to go into the {{dfsadmin}} and {{mradmin}} commands, get sent to the manager node via an extended IPC, etc. 

 
                
> Add ability to reset topologies on master nodes
> -----------------------------------------------
>
>                 Key: HADOOP-8928
>                 URL: https://issues.apache.org/jira/browse/HADOOP-8928
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: net
>            Reporter: Shinichi Yamashita
>
> For a topology decision of DataNode and TaskTracker, ScriptBasedMapping (probably TableMapping) confirms HashMap first.
> To decide topology of DataNode and TaskTracker again, it is necessary to restart NameNode and JobTracker.
> Therefore, it is necessary to change (or clear) HashMap function without restarting NameNode and JobTracker.

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