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https://issues.apache.org/jira/browse/HDFS-15796?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17375453#comment-17375453
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Stephen O'Donnell commented on HDFS-15796:
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[~Daniel Ma] I understand how a ConcurrentModificationException occurs, but
targets and excluded nodes are local variables to the method, and the calls to
getTargets is already synchronized (at least on trunk).
Can you please highlight the line the exception occurs on so we can see the
exact call which is giving the problem? Thanks.
> ConcurrentModificationException error happens on NameNode occasionally
> ----------------------------------------------------------------------
>
> Key: HDFS-15796
> URL: https://issues.apache.org/jira/browse/HDFS-15796
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: hdfs
> Affects Versions: 3.1.1
> Reporter: Daniel Ma
> Priority: Critical
> Attachments: 0001-HDFS-15796.patch
>
>
> ConcurrentModificationException error happens on NameNode occasionally.
>
> {code:java}
> 2021-01-23 20:21:18,107 | ERROR | RedundancyMonitor | RedundancyMonitor
> thread received Runtime exception. | BlockManager.java:4746
> java.util.ConcurrentModificationException
> at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:909)
> at java.util.ArrayList$Itr.next(ArrayList.java:859)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.computeReconstructionWorkForBlocks(BlockManager.java:1907)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.computeBlockReconstructionWork(BlockManager.java:1859)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.computeDatanodeWork(BlockManager.java:4862)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager$RedundancyMonitor.run(BlockManager.java:4729)
> at java.lang.Thread.run(Thread.java:748)
> {code}
>
>
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