Reduce phase behavior clarification

Bob Ippolito bob at redivi.com
Mon Jul 25 18:13:36 EDT 2011


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
>
> _______________________________________________
> riak-users mailing list
> riak-users at lists.basho.com
> http://lists.basho.com/mailman/listinfo/riak-users_lists.basho.com
>




More information about the riak-users mailing list