Question 1 remains: What happens if one invocation of a combiner outputs more than one value?
My main interest in question 2 was about instances not classes, so let me rephrase question 2 this way: What happens if an output key object is not equal to the input key object (even though both are of the same class)? Even for question 3, I did not exactly see an answer to "what happens" --- only a statement that I should not exercise that case. Thanks, Mike From: Ted Yu <[email protected]> To: [email protected] Date: 05/23/2011 03:04 PM Subject: Re: Stupid questions about combiners in ...hadoop.mapreduce 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? Thanks, Mike Spreitzer
