[jira] [Commented] (MAPREDUCE-4919) All maps hangs when set mapreduce.task.io.sort.factor to 1

["Jerry Chen (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/MAPREDUCE-4919?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13545650#comment-13545650 ] 

Jerry Chen commented on MAPREDUCE-4919:
---------------------------------------

To fix the problem, check mapreduce.task.io.sort.factor and it must be greater than 1, or throws exception:
Invalid "mapreduce.task.io.sort.factor": value

                
> 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
>
>   Original Estimate: 2h
>  Remaining Estimate: 2h
>
> 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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