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https://issues.apache.org/jira/browse/HDFS-14986?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16973339#comment-16973339
]
Xiaoqiao He commented on HDFS-14986:
------------------------------------
[~linyiqun], we did some modify when backport HDFS-14313 since there are very
diffs between branch-2.7 and trunk.
As [~Aiphag0] said above, if no synchronous control, it will throw CME, but
meet deadlock if add sync when restart DataNode. The root cause is
`BlockPoolSlice#loadDfsUsed() may return -1. And the
ReplicaCachingGetSpaceUsed#init() will blocks` when start as mentioned above.
> ReplicaCachingGetSpaceUsed throws ConcurrentModificationException
> ------------------------------------------------------------------
>
> Key: HDFS-14986
> URL: https://issues.apache.org/jira/browse/HDFS-14986
> Project: Hadoop HDFS
> Issue Type: Bug
> 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 error
> java.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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