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 <[EMAIL PROTECTED]>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?
> Mike Spreitzer