[jira] [Created] (HDFS-4937) ReplicationMonitor can infinite-loop in BlockPlacementPolicyDefault#chooseRandom()

["Kihwal Lee (JIRA)" <ji...@apache.org>]

Kihwal Lee created HDFS-4937:
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             Summary: 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: 0.23.8, 2.0.4-alpha
            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 old 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 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 previously recorded cluster size, so it will loop infinitely. This has been seen in a production environment.

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