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From "Juan P." <gordoslo...@gmail.com>
Subject Re: Comparing
Date Thu, 26 May 2011 01:04:46 GMT
Hi guys!
Any thoughts on this? Should I have sent my queries to a different
distribution list?


On Mon, May 23, 2011 at 5:36 PM, Juan P. <gordoslocos@gmail.com> wrote:

> Hi guys,
> I wanted to get your help with a couple of questions which came up while
> looking at the Hadoop Comparator/Comparable architecture.
> As I see it before each reducer operates on each key, a sorting algorithm
> is applied to them. *Why does Hadoop need to do that?*
> If I implement my own class and I intend to use it as a Key I must allow
> for instances of my class to be compared. So I have 2 choices: I can
> implement WritableComparable or I can register a WritableComparator for my
> class. Should I fail to do either, would the Job fail?
> If I register my WritableComparator which does not use the Comparable
> interface at all, does my Key need to implement WritableComparable?
> If I don't implement my Comparator and my Key implements
> WritableComparable, does it mean that Hadoop will deserialize my Keys twice?
> (once for sorting, and once for reducing)
> What is RawComparable used for?
> Thanks for your help!
> Pony

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