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Posted to common-dev@hadoop.apache.org by "Konstantin Boudnik (JIRA)" <ji...@apache.org> on 2009/04/28 17:43:30 UTC
[jira] Work logged: (HADOOP-5734) HDFS architecture documentation
describes outdated placement policy
[ https://issues.apache.org/jira/browse/HADOOP-5734?page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#action_10854 ]
Konstantin Boudnik logged work on HADOOP-5734:
----------------------------------------------
Author: Konstantin Boudnik
Created on: 28/Apr/09 08:42 AM
Start Date: 23/Apr/09 08:42 AM
Worklog Time Spent: 2h
Issue Time Tracking
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Time Spent: 2h
Remaining Estimate: 0h
> HDFS architecture documentation describes outdated placement policy
> -------------------------------------------------------------------
>
> Key: HADOOP-5734
> URL: https://issues.apache.org/jira/browse/HADOOP-5734
> Project: Hadoop Core
> Issue Type: Bug
> Components: documentation
> Affects Versions: 0.20.0
> Reporter: Konstantin Boudnik
> Priority: Minor
> Fix For: 0.21.0
>
> Attachments: HADOOP-5734.patch
>
> Time Spent: 2h
> Remaining Estimate: 0h
>
> The "Replica Placement: The First Baby Steps" section of HDFS architecture document states:
> "...
> For the common case, when the replication factor is three, HDFS's placement policy is to put one replica on one node in the local rack, another on a different node in the local rack, and the last on a different node in a different rack. This policy cuts the inter-rack write traffic which generally improves write performance.
> ..."
> However, according to the ReplicationTargetChooser.chooseTarger()'s code the actual logic is to put the second replica on a different rack as well as the third replica. So you have two replicas located on a different nodes of remote rack and one (initial replica) on the local rack's node. Thus, the sentence should say something like this:
> "For the common case, when the replication factor is three, HDFS's placement policy is to put one replica on one node in the local rack, another on a node in a different (remote) rack, and the last on a different node in the same remote rack. This policy cuts the inter-rack write traffic which generally improves write performance."
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