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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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Kihwal Lee reassigned HDFS-4937:
--------------------------------
Assignee: Kihwal Lee
> 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
> Attachments: HDFS-4937.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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