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From "Jerry Chen (JIRA)" <j...@apache.org>
Subject [jira] [Created] (MAPREDUCE-4919) All maps hangs when set mapreduce.task.io.sort.factor to 1
Date Mon, 07 Jan 2013 05:38:12 GMT
Jerry Chen created MAPREDUCE-4919:
-------------------------------------

             Summary: All maps hangs when set mapreduce.task.io.sort.factor to 1
                 Key: MAPREDUCE-4919
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-4919
             Project: Hadoop Map/Reduce
          Issue Type: Bug
          Components: client
    Affects Versions: trunk
            Reporter: Jerry Chen
            Assignee: Jerry Chen
             Fix For: trunk


In one of my testing that when I set mapreduce.task.io.sort.factor to 1, all the maps hang
and will never end. But the CPU usage for each node are very high and until killed by the
app master when time out comes, and the job failed. 

I traced the problem and found out that all the maps hangs on the final merge phase.

The while loop in computeBytesInMerges will never end with a factor of 1:

int f = 1; //in my case
int n = 16; //in my case
while (n > f || considerFinalMerge) {
  ...

  n -= (f-1);
  f = factor;
}

As the f-1 will equals 0 and n will always be 16 and the while runs for ever.

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