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From Harsh J <ha...@cloudera.com>
Subject Re: All reducers are not being utilized
Date Thu, 02 Aug 2012 10:35:26 GMT
Saurabh,

I do not see you talk about defining a custom Partitioner that can
guarantee such perfect key distribution. The default partitioner is the
HashPartitioner that can only guarantee randomized distribution (as it is
key data specific). Hence, your test here with just 3 keys is not really a
good way to test key distribution to reducers with a HashPartition. Try it
out with a large data set to see for real.

On Thu, Aug 2, 2012 at 3:55 PM, Saurabh Bajaj <Saurabh.Bajaj@mu-sigma.com>wrote:

>  Hi everyone, ****
>
> ** **
>
> I was running a MR job in java and this scenario happened:****
>
> ** **
>
> *Case 1:*
>
> Number of distinct output keys from mapper = 3****
>
> Expected # of reducers = 3****
>
> Defined set # of reducers to be called = 2****
>
> *Expected outcome:*
>
> # of reducers spawned = 2****
>
> # of keys processed under first reducer = 1****
>
> # of keys processed under second reducer = 2****
>
> *Observed outcome:*
>
> # of keys processed under first reducer = 3****
>
> # of keys processed under second reducer = 0****
>
> ** **
>
> ** **
>
> ** **
>
> *Case 2:*
>
> Number of distinct output keys from mapper = 3****
>
> Expected # of reducers = 3****
>
> Defined set # of reducers to be called = 3****
>
> *Expected outcome:*
>
> # of reducers spawned = 3****
>
> # of keys processed under first reducer = 1****
>
> # of keys processed under second reducer = 1****
>
> # of keys processed under third reducer = 1****
>
> * *
>
> *Observed outcome:*
>
> # of reducers spawned = 3****
>
> # of keys processed under first reducer = 2****
>
> # of keys processed under second reducer = 0****
>
> # of keys processed under third reducer = 1****
>
> ** **
>
> ** **
>
> Any idea why all the reducers are not utilized?****
>
> ** **
>
> Saurabh Bajaj *|* Senior Business Analyst *|* +91 9986588089 *|*
> www.mu-sigma.com* **|*
>
> ** **
>
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-- 
Harsh J

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