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Re: more reduce tasks
Vinod Kumar Vavilapalli 2013-01-04, 04:45

Is it that you want the parallelism but a single final output? Assuming your first job's reducers generate a small output, another stage is the way to go. If not, second stage won't help. What exactly are your objectives?

Thanks,
+Vinod

On Jan 3, 2013, at 1:11 PM, Pavel Hančar wrote:

>   Hello,
> I'd like to use more than one reduce task with Hadoop Streaming and I'd like to have only one result. Is it possible? Or should I run one more job to merge the result? And is it the same with non-streaming jobs? Below you see, I have 5 results for mapred.reduce.tasks=5.
>
> $ hadoop jar /packages/run.64/hadoop-0.20.2-cdh3u1/contrib/streaming/hadoop-streaming-0.20.2-cdh3u1.jar  -D mapred.reduce.tasks=5 -mapper /bin/cat -reducer /tmp/wcc -file /tmp/wcc -file /bin/cat -input /user/hadoopnlp/1gb -output 1gb.wc
> .
> .
> .
> 13/01/03 22:00:03 INFO streaming.StreamJob:  map 100%  reduce 100%
> 13/01/03 22:00:07 INFO streaming.StreamJob: Job complete: job_201301021717_0038
> 13/01/03 22:00:07 INFO streaming.StreamJob: Output: 1gb.wc
> $ hadoop dfs -cat 1gb.wc/part-*
> 472173052
> 165736187
> 201719914
> 184376668
> 163872819
> $
>
> where /tmp/wcc contains
> #!/bin/bash
> wc -c
>
> Thanks for any answer,
>  Pavel Hančar

+
Pavel Hančar 2013-01-04, 08:35
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Harsh J 2013-01-05, 07:57
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Pavel Hančar 2013-01-05, 14:32
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Chen He 2013-01-04, 04:55
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bejoy.hadoop@... 2013-01-04, 05:24
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Chen He 2013-01-04, 05:32
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Robert Dyer 2013-01-04, 05:55