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From Ted Yu <yuzhih...@gmail.com>
Subject Re: Stupid questions about combiners in ...hadoop.mapreduce
Date Mon, 23 May 2011 19:03:22 GMT
Questions 2 and 3 can be answered relatively easily:
Remember, the output of the combiner is going to be consumed by the reducer.
So the output key/vlaue classes of the combiner have to align with the input
key/vlaue classes of the reducer.

On Mon, May 23, 2011 at 11:32 AM, Mike Spreitzer <mspreitz@us.ibm.com>wrote:

> In general, the Java interfaces say that one invocation of a combiner
> (technically, a Class<? *extends* Reducer>) can output multiple
> (key,value) pairs.  So:
>
> What happens if one invocation of a combiner outputs more than one value?
>
> What happens if an output key is different from the input key?
>
> What happens if an output value is of a different class than the class of
> the input values?
>
> Thanks,
> Mike Spreitzer
>

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