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From Arun C Murthy <ar...@yahoo-inc.com>
Subject Re: Default Combiner or default combining behaviour?
Date Thu, 20 Mar 2008 23:47:50 GMT

On Mar 20, 2008, at 3:56 PM, Otis Gospodnetic wrote:

> Hi,
>
> The MapReduce tutorial mentions Combiners only in passing.  Is  
> there a default Combiner or default combining behaviour?
>

No, there is *no* default combiner at all. It has to be explicitly  
set in the JobConf to take effect.

Arun

> Concretely, I want to make sure that records are not getting  
> combined behind the scenes in some way without me seeing it, and  
> causing me to lose data.  For instance, if there is a default  
> Combiner or default combining behaviour that collapses multiple  
> records with identical keys and values into a single record, I'd  
> like to avoid that.  Instead of blindly collapsing identical  
> records, I'd want to aggregate their values and emit the aggregate.
>
> Thanks,
> Otis
> --
> Sematext -- http://sematext.com/ -- Lucene - Solr - Nutch
>
>


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