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From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-5837) dfs.namenode.replication.considerLoad does not consider decommissioned nodes
Date Sat, 08 Feb 2014 09:26:19 GMT

    [ https://issues.apache.org/jira/browse/HDFS-5837?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13895492#comment-13895492
] 

Hadoop QA commented on HDFS-5837:
---------------------------------

{color:green}+1 overall{color}.  Here are the results of testing the latest attachment 
  http://issues.apache.org/jira/secure/attachment/12627785/HDFS-5837_C.patch
  against trunk revision .

    {color:green}+1 @author{color}.  The patch does not contain any @author tags.

    {color:green}+1 tests included{color}.  The patch appears to include 1 new or modified
test files.

    {color:green}+1 javac{color}.  The applied patch does not increase the total number of
javac compiler warnings.

    {color:green}+1 javadoc{color}.  There were no new javadoc warning messages.

    {color:green}+1 eclipse:eclipse{color}.  The patch built with eclipse:eclipse.

    {color:green}+1 findbugs{color}.  The patch does not introduce any new Findbugs (version
1.3.9) warnings.

    {color:green}+1 release audit{color}.  The applied patch does not increase the total number
of release audit warnings.

    {color:green}+1 core tests{color}.  The patch passed unit tests in hadoop-hdfs-project/hadoop-hdfs.

    {color:green}+1 contrib tests{color}.  The patch passed contrib unit tests.

Test results: https://builds.apache.org/job/PreCommit-HDFS-Build/6088//testReport/
Console output: https://builds.apache.org/job/PreCommit-HDFS-Build/6088//console

This message is automatically generated.

> dfs.namenode.replication.considerLoad does not consider decommissioned nodes
> ----------------------------------------------------------------------------
>
>                 Key: HDFS-5837
>                 URL: https://issues.apache.org/jira/browse/HDFS-5837
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: namenode
>    Affects Versions: 2.0.0-alpha, 3.0.0, 2.0.6-alpha, 2.2.0
>            Reporter: Bryan Beaudreault
>            Assignee: Tao Luo
>         Attachments: HDFS-5837.patch, HDFS-5837_B.patch, HDFS-5837_C.patch, HDFS-5837_branch_2.2.0.patch
>
>
> In DefaultBlockPlacementPolicy, there is a setting dfs.namenode.replication.considerLoad
which tries to balance the load of the cluster when choosing replica locations.  This code
does not take into account decommissioned nodes.
> The code for considerLoad calculates the load by doing:  TotalClusterLoad / numNodes.
 However, numNodes includes decommissioned nodes (which have 0 load).  Therefore, the average
load is artificially low.  Example:
> TotalLoad = 250
> numNodes = 100
> decommissionedNodes = 70
> remainingNodes = numNodes - decommissionedNodes = 30
> avgLoad = 250/100 = 2.50
> trueAvgLoad = 250 / 30 = 8.33
> If the real load of the remaining 30 nodes is (on average) 8.33, this is more than 2x
the calculated average load of 2.50.  This causes these nodes to be rejected as replica locations.
The final result is that all nodes are rejected, and no replicas can be placed.  
> See exceptions printed from client during this scenario: https://gist.github.com/bbeaudreault/49c8aa4bb231de54e9c1



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