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From "Devaraj Das (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-723) Race condition exists in the method MapOutputLocation.getFile
Date Wed, 15 Nov 2006 16:46:37 GMT
Race condition exists in the method MapOutputLocation.getFile
-------------------------------------------------------------

                 Key: HADOOP-723
                 URL: http://issues.apache.org/jira/browse/HADOOP-723
             Project: Hadoop
          Issue Type: Bug
          Components: mapred
            Reporter: Devaraj Das


There seems to be a race condition in the way the Reduces copy the map output files from the
Maps. If a copier is blocked in the connect method (in the beginning of the method MapOutputLocation.getFile)
to a Jetty on a Map, and the MapCopyLeaseChecker detects that the copier was idle for too
long, it will go ahead and issue a interrupt (read 'kill') to this thread and create a new
Copier thread. However, the copier, currently blocked trying to connect to Jetty on a Map,
doesn't actually get killed until the connect timeout expires and as soon as the connect comes
out (with an IOException), it will delete the map output file which actually could have been
(successfully) created by the new Copier thread. This leads to the Sort phase for that reducer
failing with a FileNotFoundException.
One simple way to fix this is to not delete the file if the file was not created within this
getFile method.

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