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Date: Mon, 31 Oct 2011 13:41:47 +0100
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Subject: Re: Combiners
From: Mathias Herberts <mathias.herberts@gmail.com>
To: common-user@hadoop.apache.org
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> Yes. We've talked about adding various checks, but I don't think anyone has
> added them. We obviously have the input key and one option would be to
> ignore the output key.

ok.

>
>> Since a Combiner is simply a Reducer with no other constraints,
>>
>
> That isn't true. Combiners are required to be:

When I meant 'Reducer with no other constraints' I meant
Job.setCombinerClass takes a Class<? extends Reducer>, not a Combiner
class which enforces stricter constraints.

Thanks for listing the 5 requirements, if you don't mind I'll add them
to the Hadoop MapReducer Poster.