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https://issues.apache.org/jira/browse/MAPREDUCE-4919?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jerry Chen updated MAPREDUCE-4919:
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Status: Patch Available (was: Open)
mapreduce.task.io.sort.factor is checked and it must be greater than 1 to fix
the hang of the mappers. Please kindly help review.
> 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
>
> Attachments: MAPREDUCE-4919.patch
>
> 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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