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https://issues.apache.org/jira/browse/HDFS-15796?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17375386#comment-17375386
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Stephen O'Donnell commented on HDFS-15796:
------------------------------------------
I don't think the patch will help anything here. All the methods on
PendingReconstruction are already synchronized, eg:
{code}
List<DatanodeStorageInfo> getTargets(BlockInfo block) {
synchronized (pendingReconstructions) {
PendingBlockInfo found = pendingReconstructions.get(block);
if (found != null) {
return found.targets;
}
}
return null;
}
{code}
You posted a code snippet above, but there are no line numbers with it, so I
cannot see what line the exception was thrown. Can you tell me which is line is
1907 in your code snippet above?
> 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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