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From "Robert Joseph Evans (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-4506) EofException / 'connection reset by peer' while copying map output
Date Thu, 02 Aug 2012 13:29:02 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-4506?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13427310#comment-13427310
] 

Robert Joseph Evans commented on MAPREDUCE-4506:
------------------------------------------------

Piotr,

I agree that it is ugly to see the exception come out, but I am not really sure that your
fix is the right one for 1.0.  Making the memory manager blocking means that the jetty thread
on the task tracker will not be able to serve up results to others.  This could potentially
slow down processing for very large jobs.  I think it would be a lot better to do something
like that on trunk, where the problem also exists, but the node manager uses netty instead
of jetty so it is not a full thread that is blocked but just some memory and a file descriptor.
 Assuming that we have a timeout on how long the thread waits for memory to become available.
                
> EofException / 'connection reset by peer' while copying map output 
> -------------------------------------------------------------------
>
>                 Key: MAPREDUCE-4506
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-4506
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>    Affects Versions: 1.0.3
>         Environment: Ubuntu Linux 12.04 LTS, 64-bit, Java 6 update 33
>            Reporter: Piotr Kołaczkowski
>            Priority: Minor
>         Attachments: RamManager.patch, ReduceTask.patch
>
>
> When running complex mapreduce jobs with many mappers and reducers (e.g. 8 mappers, 8
reducers on a 8 core machine), sometimes the following exceptions pop up in the logs during
the shuffle phase:
> {noformat}
> WARN [570516323@qtp-2060060479-164] 2012-07-19 02:50:21,229 TaskTracker.java (line 3894)
getMapOutput(attempt_201207161621_0217_m_000071_0,0) failed :
> org.mortbay.jetty.EofException
>         at org.mortbay.jetty.HttpGenerator.flush(HttpGenerator.java:787)
>         at org.mortbay.jetty.AbstractGenerator$Output.flush(AbstractGenerator.java:568)
>         at org.mortbay.jetty.HttpConnection$Output.flush(HttpConnection.java:1005)
>         at org.mortbay.jetty.AbstractGenerator$Output.write(AbstractGenerator.java:648)
>         at org.mortbay.jetty.AbstractGenerator$Output.write(AbstractGenerator.java:579)
>         at org.apache.hadoop.mapred.TaskTracker$MapOutputServlet.doGet(TaskTracker.java:3872)
>         at javax.servlet.http.HttpServlet.service(HttpServlet.java:707)
>         at javax.servlet.http.HttpServlet.service(HttpServlet.java:820)
>         at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
>         at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166)
>         at org.apache.hadoop.http.HttpServer$QuotingInputFilter.doFilter(HttpServer.java:835)
>         at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
>         at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
>         at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
>         at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
>         at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
>         at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418)
>         at org.mortbay.jetty.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:230)
>         at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
>         at org.mortbay.jetty.Server.handle(Server.java:326)
>         at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
>         at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:923)
>         at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:547)
>         at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:212)
>         at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
>         at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:409)
>         at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)
> Caused by: java.io.IOException: Connection reset by peer
>         at sun.nio.ch.FileDispatcher.write0(Native Method)
>         at sun.nio.ch.SocketDispatcher.write(SocketDispatcher.java:29)
>         at sun.nio.ch.IOUtil.writeFromNativeBuffer(IOUtil.java:72)
>         at sun.nio.ch.IOUtil.write(IOUtil.java:43)
>         at sun.nio.ch.SocketChannelImpl.write(SocketChannelImpl.java:334)
>         at org.mortbay.io.nio.ChannelEndPoint.flush(ChannelEndPoint.java:169)
>         at org.mortbay.io.nio.SelectChannelEndPoint.flush(SelectChannelEndPoint.java:221)
>         at org.mortbay.jetty.HttpGenerator.flush(HttpGenerator.java:721)
> {noformat}
> The problem looks like some network problems at first, however it turns out that hadoop
shuffleInMemory sometimes deliberately closes map-output-copy connections just to reopen them
a few milliseconds later, because of temporary unavailability of free memory. Because the
sending side does not expect this, an exception is thrown. Additionally this leads to wasting
resources on the sender side, which does more work than required serving additional requests.


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