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From "Tao Luo (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-5837) dfs.namenode.replication.considerLoad does not consider decommissioned nodes
Date Wed, 05 Feb 2014 23:52:13 GMT

     [ https://issues.apache.org/jira/browse/HDFS-5837?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Tao Luo updated HDFS-5837:
--------------------------

    Status: Patch Available  (was: Open)

> 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: 2.2.0, 2.0.6-alpha, 2.0.0-alpha
>            Reporter: Bryan Beaudreault
>            Assignee: Tao Luo
>         Attachments: HDFS-5837.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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