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https://issues.apache.org/jira/browse/HADOOP-951?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12468811
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Konstantin Shvachko commented on HADOOP-951:
--------------------------------------------
IMO this issue is the race condition bug and should be fixed in a traditional
way.
ConcurrentHashMap is an interesting concept, we should definitely take it into
consideration
when we decide to optimize our data structures and locking.
I cannot estimate the amount of changes the name-node code will require at this
point
if we introduce ConcurrentHashMap because of its different semantics.
And we should not forget in chooseTargets() the name-node is under the global
lock.
Fine grained locking under that lock seems to be a waste of resources.
> java.util.ConcurrentModificationException in FSNamesystem.chooseTargets
> -------------------------------------------------------------------------
>
> Key: HADOOP-951
> URL: https://issues.apache.org/jira/browse/HADOOP-951
> Project: Hadoop
> Issue Type: Bug
> Components: dfs
> Affects Versions: 0.10.1
> Reporter: Koji Noguchi
>
> 2007-01-26 01:14:37,509 INFO org.apache.hadoop.ipc.Server: IPC Server handler
> 7 on 8020 call error: java.io.IOException:
> java.util.ConcurrentModificationException
> java.io.IOException: java.util.ConcurrentModificationException
> at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:449)
> at java.util.AbstractList$Itr.next(AbstractList.java:420)
> at org.apache.hadoop.dfs.FSNamesystem.chooseTargets(FSNamesystem.java:2282)
> at org.apache.hadoop.dfs.FSNamesystem.startFile(FSNamesystem.java:484)
> at org.apache.hadoop.dfs.NameNode.create(NameNode.java:238)
> at sun.reflect.GeneratedMethodAccessor60.invoke(Unknown Source)
> at
> sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
> at java.lang.reflect.Method.invoke(Method.java:585)
> at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:337)
> at org.apache.hadoop.ipc.Server$Handler.run(Server.java:538)
> Not sure if it's related, but this exception happend when namenode was
> replicating many blocks.
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