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https://issues.apache.org/jira/browse/MAPREDUCE-1372?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12800728#action_12800728
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Amar Kamat commented on MAPREDUCE-1372:
---------------------------------------
JobTracker.addHostToNodeMapping() doesnt need any synchronization because the
first call it makes is to NetworkTopology.getNode() which is synchonized
internally. JobTracker.hostnameToNodeMap (which gets modified in
JobTracker.addHostToNodeMapping()) is synchronized collection and hence it
doesnt need any explicit synchronization. Hence I think the
[patch|https://issues.apache.org/jira/secure/attachment/12430341/M1372-1.patch]
Chris uploaded should suffice.
> ConcurrentModificationException in JobInProgress
> ------------------------------------------------
>
> Key: MAPREDUCE-1372
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-1372
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: jobtracker
> Affects Versions: 0.20.1
> Reporter: Amareshwari Sriramadasu
> Priority: Blocker
> Fix For: 0.21.0
>
> Attachments: M1372-0.patch, M1372-1.patch, M1372-2.patch
>
>
> We have seen the following ConcurrentModificationException in one of our
> clusters
> {noformat}
> java.io.IOException: java.util.ConcurrentModificationException
> at java.util.HashMap$HashIterator.nextEntry(HashMap.java:793)
> at java.util.HashMap$KeyIterator.next(HashMap.java:828)
> at
> org.apache.hadoop.mapred.JobInProgress.findNewMapTask(JobInProgress.java:2018)
> at
> org.apache.hadoop.mapred.JobInProgress.obtainNewMapTask(JobInProgress.java:1077)
> at
> org.apache.hadoop.mapred.CapacityTaskScheduler$MapSchedulingMgr.obtainNewTask(CapacityTaskScheduler.java:796)
> at
> org.apache.hadoop.mapred.CapacityTaskScheduler$TaskSchedulingMgr.getTaskFromQueue(CapacityTaskScheduler.java:589)
> at
> org.apache.hadoop.mapred.CapacityTaskScheduler$TaskSchedulingMgr.assignTasks(CapacityTaskScheduler.java:677)
> at
> org.apache.hadoop.mapred.CapacityTaskScheduler$TaskSchedulingMgr.access$500(CapacityTaskScheduler.java:348)
> at
> org.apache.hadoop.mapred.CapacityTaskScheduler.addMapTask(CapacityTaskScheduler.java:1397)
> at
> org.apache.hadoop.mapred.CapacityTaskScheduler.assignTasks(CapacityTaskScheduler.java:1349)
> at org.apache.hadoop.mapred.JobTracker.heartbeat(JobTracker.java:2976)
> at sun.reflect.GeneratedMethodAccessor5.invoke(Unknown Source)
> at
> sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
> at java.lang.reflect.Method.invoke(Method.java:597)
> at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:508)
> at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:959)
> at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:955)
> at java.security.AccessController.doPrivileged(Native Method)
> at javax.security.auth.Subject.doAs(Subject.java:396)
> at org.apache.hadoop.ipc.Server$Handler.run(Server.java:953)
> {noformat}
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