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https://issues.apache.org/jira/browse/HDFS-14986?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16973305#comment-16973305
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Xiaoqiao He commented on HDFS-14986:
------------------------------------
we meet very similar case (ConcurrentModificationException or DeadLock) when
backport HDFS-14313 to branch-2.7, and I believe there is still some space to
improve current implementation.
[~Aiphag0] may have some more information. Would you like to offer our patch
here?
> ReplicaCachingGetSpaceUsed throws ConcurrentModificationException
> ------------------------------------------------------------------
>
> Key: HDFS-14986
> URL: https://issues.apache.org/jira/browse/HDFS-14986
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: datanode, performance
> Reporter: Ryan Wu
> Assignee: Ryan Wu
> Priority: Major
>
> Running DU across lots of disks is very expensive . We applied the patch
> HDFS-14313 to get used space from ReplicaInfo in memory.However, new du
> threads throw the exception
> {code:java}
> // 2019-11-08 18:07:13,858 ERROR
> [refreshUsed-/home/vipshop/hard_disk/7/dfs/dn/current/BP-1203969992-XXXX-1450855658517]
>
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.ReplicaCachingGetSpaceUsed:
> ReplicaCachingGetSpaceUsed refresh
> errorjava.util.ConcurrentModificationException: Tree has been modified
> outside of iterator at
> org.apache.hadoop.hdfs.util.FoldedTreeSet$TreeSetIterator.checkForModification(FoldedTreeSet.java:311)
> at
> org.apache.hadoop.hdfs.util.FoldedTreeSet$TreeSetIterator.hasNext(FoldedTreeSet.java:256)
> at java.util.AbstractCollection.addAll(AbstractCollection.java:343) at
> java.util.HashSet.<init>(HashSet.java:120) at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl.deepCopyReplica(FsDatasetImpl.java:1052)
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.ReplicaCachingGetSpaceUsed.refresh(ReplicaCachingGetSpaceUsed.java:73)
> at
> org.apache.hadoop.fs.CachingGetSpaceUsed$RefreshThread.run(CachingGetSpaceUsed.java:178)
> at java.lang.Thread.run(Thread.java:748)
> {code}
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