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From Manoj Khangaonkar <khangaon...@gmail.com>
Subject Re: Map Reduce Question
Date Sat, 18 Aug 2012 01:20:36 GMT
One usage of these is in a secondary sort , which is used , when you
want the output values from Map sorted (within a key).

You implement a KeyComparator and tell mapreduce to use it to order
the keys using a composite key.

To ensure that during partioning & Grouping , all the records for a
key go to the same reducer
you need to define and set a Partitioner and ValueGroupingComparator.

search for Secondary Sort for more on this topic



On Fri, Aug 17, 2012 at 12:00 PM, Anbarasan Murthy
<anbu992003@hotmail.com> wrote:
> Hi,
> I have a question in mapreduce api.
> Would like to know the significance of the following items under jobconf
> class.
> ValueGroupingComparator
> KeyComparator
> Thanks,
> Anbu.


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