Reduce phase behavior clarification

Brian Rowe rowe at muxspace.com
Tue Jul 26 16:13:27 EDT 2011


https://github.com/basho/riak_wiki/pull/139


On Tue, Jul 26, 2011 at 9:35 AM, Sean Cribbs <sean at basho.com> wrote:
> Bob is right, it's a simple typo. Please send a pull request or open an
> issue on the tracker.  https://github.com/basho/riak_wiki/issues
>
> On Mon, Jul 25, 2011 at 6:13 PM, Bob Ippolito <bob at redivi.com> wrote:
>>
>> It sounds like there is a typo, I would assume that it should be "the
>> input of later evaluations will include the output of earlier
>> evaluations". It's not really a reduction otherwise.
>>
>> On Mon, Jul 25, 2011 at 3:03 PM, Brian Rowe <rowe at muxspace.com> wrote:
>> > Hello,
>> >
>> > I see the following on the Basho wiki for Riak [1]:
>> >
>> >  The important thing to understand is that the function defining the
>> > reduce phase may be evaluated multiple times, and the input of later
>> > evaluations will include the input of earlier evaluations.
>> >  For example, a reduce phase may implement the set-union function. In
>> > that case, the first set of inputs might be [1,2,2,3], and the output
>> > would be [1,2,3]. When the phase receives more inputs, say [3,4,5],
>> > the function will be called with the concatentation of the two lists:
>> > [1,2,3,4,5].
>> >
>> > This description isn't clear to me as the behavior I'm seeing is that
>> > the _output_ of earlier evaluations is included as input to later
>> > evaluations. Unfortunately, the example yields the same results
>> > irrespective of whether it is the input or the output of the first
>> > evaluation, so it doesn't clear anything up.
>> >
>> > Thanks,
>> > Brian
>> >
>> >
>> > [1] http://wiki.basho.com/MapReduce.html
>> >
>> > _______________________________________________
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>> > riak-users at lists.basho.com
>> > http://lists.basho.com/mailman/listinfo/riak-users_lists.basho.com
>> >
>>
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>
>
> --
> Sean Cribbs <sean at basho.com>
> Developer Advocate
> Basho Technologies, Inc.
> http://www.basho.com/
>




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