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https://issues.apache.org/jira/browse/HDFS-15796?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17376429#comment-17376429
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Daniel Ma edited comment on HDFS-15796 at 7/7/21, 11:57 AM:
------------------------------------------------------------

[~sodonnell]

yes, I also think it is a better way:
{code:java}
//
A better approach, may be to return a new ArrayList from getTargets, eg:
{code}
The patch is updated, Pls help to review.


was (Author: daniel ma):
[~sodonnell]

yes, I totally agree with the solution you raised.

I will work on it, and update the patch

> 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, 0002-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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