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https://issues.apache.org/jira/browse/HDFS-4937?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Yi Liu reopened HDFS-4937:
--------------------------

> ReplicationMonitor can infinite-loop in 
> BlockPlacementPolicyDefault#chooseRandom()
> ----------------------------------------------------------------------------------
>
>                 Key: HDFS-4937
>                 URL: https://issues.apache.org/jira/browse/HDFS-4937
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: namenode
>    Affects Versions: 2.0.4-alpha, 0.23.8
>            Reporter: Kihwal Lee
>            Assignee: Kihwal Lee
>              Labels: BB2015-05-TBR
>             Fix For: 3.0.0, 2.7.2
>
>         Attachments: HDFS-4937.patch, HDFS-4937.v1.patch, HDFS-4937.v2.patch
>
>
> When a large number of nodes are removed by refreshing node lists, the 
> network topology is updated. If the refresh happens at the right moment, the 
> replication monitor thread may stuck in the while loop of {{chooseRandom()}}. 
> This is because the cached cluster size is used in the terminal condition 
> check of the loop. This usually happens when a block with a high replication 
> factor is being processed. Since replicas/rack is also calculated beforehand, 
> no node choice may satisfy the goodness criteria if refreshing removed racks. 
> All nodes will end up in the excluded list, but the size will still be less 
> than the cached cluster size, so it will loop infinitely. This was observed 
> in a production environment.



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