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https://issues.apache.org/jira/browse/HADOOP-5734?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12703496#action_12703496
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Hadoop QA commented on HADOOP-5734:
-----------------------------------

+1 overall.  Here are the results of testing the latest attachment 
  http://issues.apache.org/jira/secure/attachment/12406316/HADOOP-5734.patch
  against trunk revision 769174.

    +1 @author.  The patch does not contain any @author tags.

    +0 tests included.  The patch appears to be a documentation patch that 
doesn't require tests.

    +1 javadoc.  The javadoc tool did not generate any warning messages.

    +1 javac.  The applied patch does not increase the total number of javac 
compiler warnings.

    +1 findbugs.  The patch does not introduce any new Findbugs warnings.

    +1 Eclipse classpath. The patch retains Eclipse classpath integrity.

    +1 release audit.  The applied patch does not increase the total number of 
release audit warnings.

    +1 core tests.  The patch passed core unit tests.

    +1 contrib tests.  The patch passed contrib unit tests.

Test results: 
http://hudson.zones.apache.org/hudson/job/Hadoop-Patch-vesta.apache.org/253/testReport/
Findbugs warnings: 
http://hudson.zones.apache.org/hudson/job/Hadoop-Patch-vesta.apache.org/253/artifact/trunk/build/test/findbugs/newPatchFindbugsWarnings.html
Checkstyle results: 
http://hudson.zones.apache.org/hudson/job/Hadoop-Patch-vesta.apache.org/253/artifact/trunk/build/test/checkstyle-errors.html
Console output: 
http://hudson.zones.apache.org/hudson/job/Hadoop-Patch-vesta.apache.org/253/console

This message is automatically generated.

> HDFS architecture documentation describes outdated placement policy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
>
>
> 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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