Reduce phase behavior clarification

Sean Cribbs sean at basho.com
Tue Jul 26 09:35:33 EDT 2011


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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