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From "Kihwal Lee (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-4937) ReplicationMonitor can infinite-loop in BlockPlacementPolicyDefault#chooseRandom()
Date Tue, 25 Jun 2013 21:49:20 GMT

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

Kihwal Lee updated HDFS-4937:
-----------------------------

    Description: 
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.

  was:
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 has been seen in a production environment.

    
> 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
>
> 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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