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From "Binglin Chang (JIRA)" <j...@apache.org>
Subject [jira] [Created] (MAPREDUCE-2541) Race Condition in IndexCache(readIndexFileToCache,removeMap) causes value of totalMemoryUsed corrupt, which may cause TaskTracker continue throw Exception
Date Sat, 28 May 2011 17:36:47 GMT
Race Condition in IndexCache(readIndexFileToCache,removeMap) causes value of totalMemoryUsed
corrupt, which may cause TaskTracker continue throw Exception
----------------------------------------------------------------------------------------------------------------------------------------------------------

                 Key: MAPREDUCE-2541
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-2541
             Project: Hadoop Map/Reduce
          Issue Type: Bug
          Components: tasktracker
    Affects Versions: 0.21.0, 0.20.1, 0.22.0, 0.23.0
         Environment: all
            Reporter: Binglin Chang
            Priority: Critical


The race condition goes like this:
Thread1: readIndexFileToCache()  totalMemoryUsed.addAndGet(newInd.getSize())
Thread2: removeMap() totalMemoryUsed.addAndGet(-info.getSize());
When SpillRecord is being read from fileSystem, client kills the job, info.getSize() equals
0, so in fact totalMemoryUsed is not reduced, but after thread1 finished reading SpillRecord,
it adds the real index size to totalMemoryUsed, which makes the value of totalMemoryUsed wrong(larger).
When this value(totalMemoryUsed) exceeds totalMemoryAllowed (this usually happens when a vary
large job with vary large reduce number is killed by the user, probably because the user sets
a wrong reduce number by mistake), and actually indexCache has not cache anything, freeIndexInformation()
will throw exception constantly.

A quick fix for this issue is to make removeMap() do nothing, let freeIndexInformation() do
this job only.


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