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https://issues.apache.org/jira/browse/HADOOP-1182?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12485267
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dhruba borthakur commented on HADOOP-1182:
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It would help us a lot if you can monitor the CPU usage on the namenode when
this occurs. Was the CPU close to 100%? Also, do you see messages of the
following type in the namenode log?
"Call queue overflow discarding oldest call"
> scalability issue with filecache in large clusters
> --------------------------------------------------
>
> Key: HADOOP-1182
> URL: https://issues.apache.org/jira/browse/HADOOP-1182
> Project: Hadoop
> Issue Type: Bug
> Components: mapred
> Affects Versions: 0.12.1
> Reporter: Christian Kunz
>
> When using filecache to distribute supporting files for map/reduce
> applications in a 1000 node cluster, many map tasks fail because of
> timeouts. There was no such problem using a 200 node cluster for the same
> applications with comparable input data. Either the whole job fails because
> of too many map failures, or even worse, some map tasks hang indefinitely.
> java.net.SocketTimeoutException: timed out waiting for rpc response
> at org.apache.hadoop.ipc.Client.call(Client.java:473)
> at org.apache.hadoop.ipc.RPC$Invoker.invoke(RPC.java:163)
> at org.apache.hadoop.dfs.$Proxy1.exists(Unknown Source)
> at org.apache.hadoop.dfs.DFSClient.exists(DFSClient.java:320)
> at
> org.apache.hadoop.dfs.DistributedFileSystem$RawDistributedFileSystem.exists(DistributedFileSystem.java:170)
> at
> org.apache.hadoop.dfs.DistributedFileSystem$RawDistributedFileSystem.open(DistributedFileSystem.java:125)
> at
> org.apache.hadoop.fs.ChecksumFileSystem$FSInputChecker.(ChecksumFileSystem.java:110)
> at
> org.apache.hadoop.fs.ChecksumFileSystem.open(ChecksumFileSystem.java:330)
> at org.apache.hadoop.fs.FileSystem.open(FileSystem.java:245)
> at
> org.apache.hadoop.filecache.DistributedCache.createMD5(DistributedCache.java:327)
> at
> org.apache.hadoop.filecache.DistributedCache.ifExistsAndFresh(DistributedCache.java:253)
> at
> org.apache.hadoop.filecache.DistributedCache.localizeCache(DistributedCache.java:169)
> at
> org.apache.hadoop.filecache.DistributedCache.getLocalCache(DistributedCache.java:86)
> at org.apache.hadoop.mapred.TaskRunner.run(TaskRunner.java:117)
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