[jira] Commented: (HADOOP-971) DFS Scalabilty: Improve name node performance by adding a hostname to datanodes map

["dhruba borthakur (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-971?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12486471 ] 

dhruba borthakur commented on HADOOP-971:
-----------------------------------------

+1. I have been running this code successfully on a 1800 node dfs cluster. 

> DFS Scalabilty: Improve name node performance by adding a hostname to datanodes map
> -----------------------------------------------------------------------------------
>
>                 Key: HADOOP-971
>                 URL: https://issues.apache.org/jira/browse/HADOOP-971
>             Project: Hadoop
>          Issue Type: Improvement
>          Components: dfs
>    Affects Versions: 0.11.0
>            Reporter: Hairong Kuang
>         Assigned To: Hairong Kuang
>         Attachments: Host2NodesMap.patch
>
>
> A name node currently maintains a datanode map which maps a storage id to a dataNodeDescriptor. When the name node needs to get a datanodeDescriptor by its name (hostname:port#) or by its host name, it has to iterate through the data node set, which is very inefficent. I'd like to add an additional map that maps a host name to an array list of DatanodeDescriptors that contains all the data nodes running on the host. Since most of time a node runs only one data node, the intial size of the array list is set to be 1.

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