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From Ted Dunning <tdunn...@maprtech.com>
Subject Re: Cartesian product in hadoop
Date Thu, 18 Apr 2013 18:52:45 GMT
It is rarely practical to do exhaustive comparisons on datasets of this

The method used is to heuristically prune the cartesian product set and
only examine pairs that have a high likelihood of being near.

This can be done in many ways.  Your suggestion of doing a map-side join is
a reasonable one, but it will be much slower than methods where you can
prune the comparisons.

On Thu, Apr 18, 2013 at 9:47 AM, zheyi rong <zheyi.rong@gmail.com> wrote:

> Dear all,
> I am writing to kindly ask for ideas of doing cartesian product in hadoop.
> Specifically, now I have two datasets, each of which contains 20million
> lines.
> I want to do cartesian product on these two datasets, comparing lines
> pairwisely.
> The output of each comparison can be mostly filtered by a function ( we do
> not output the
> whole result of this cartesian product, but only a small part).
> I guess one good way is to pass one block from dataset1 and another block
> from dataset2
> to a mapper, then let the mappers do the product in memory to avoid IO.
> Any suggestions?
> Thank you very much.
> Regards,
> Zheyi Rong

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