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From "Hairong Kuang (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-972) Improve the rack-aware replica placement performance
Date Thu, 15 Feb 2007 01:30:05 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-972?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12473279
] 

Hairong Kuang commented on HADOOP-972:
--------------------------------------

The attached patch has a minor modification to the proposal. NetworkTopology adds one chooseRandom
method. When the scope starts with ~, it means to choose a datanode excluding from scope;
otherwise, it means to choose a random data node from scope.

> Improve the rack-aware replica placement performance
> ----------------------------------------------------
>
>                 Key: HADOOP-972
>                 URL: https://issues.apache.org/jira/browse/HADOOP-972
>             Project: Hadoop
>          Issue Type: Improvement
>          Components: dfs
>    Affects Versions: 0.11.0
>            Reporter: Hairong Kuang
>         Assigned To: Hairong Kuang
>             Fix For: 0.12.0
>
>         Attachments: rack_performance.patch
>
>
> This issue aims to improve the rack-aware replica placement performance. A major idea
is to avoid constructing lists of possible targets for random selection in chooseTarget, which
currently needs interating all DatanodeDescriptors. I plan to change the NetworkTopology data
structure as follow:
> 1. each InnerNode stores its childrens as a list;
> 2. each InnerNode adds a new field numberOfLeaves the total number of leaves (i.e. data
nodes) in its subtree. 
> NetworkTopology will support two new methods:
> 1. DatanodeDescriptor chooseRandom( String scope): it randomly choose one leave from
scope.
> 2. DatanodeDescriptor chooseRandomExclude(String excludedScope): it randomly choose one
leave from ~scope
> In addition, Issue 971 will also help improve the performance of the rack-aware DFS patch.

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