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From "Milind Bhandarkar (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-972) Improve the rack-aware replica placement performance
Date Fri, 16 Feb 2007 00:02:05 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-972?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12473569
] 

Milind Bhandarkar commented on HADOOP-972:
------------------------------------------

A few comments: 

Replicator class needs to move out of FSNameSystem, by supplying it the clusterMap at construction.
It adds about 450 lines of code to FSNamesystem.java, which is already quite big, affecting
readablity.

We should rename that class ReplicaChooser or some such thing. The name Replicator creates
a false impression.

> 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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