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Posted to common-user@hadoop.apache.org by Dennis Kubes <nu...@dragonflymc.com> on 2006/04/13 00:19:54 UTC

Key Merging and Mapreduce

Can someone explain how duplicate keys are merged inside of a reduce 
program to give multiple values in the Iterator for the reduce operation.? 

I think it is happening in the sort of the sequence file butI also see 
the CombiningCollector.  I was able to write a MapReduce program 
successfully and I am getting values with the same keys merged even when 
I don't use the CombiningCollector.  Is the CombiningCollector even used 
anymore?  I just want to understand more about what is happening under 
the hood.

Dennis