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From adeelmahmood <adeelmahm...@gmail.com>
Subject do all mappers finish before reducer starts
Date Fri, 29 Jan 2010 21:10:50 GMT

I just have a conceptual question. My understanding is that all the mappers
have to complete their job for the reducers to start working because mappers
dont know about each other so we need values for a given key from all the
different mappers so we have to wait until all mappers have collectively
given the system all possible values for a key .so that then that can be
passed on the reducer .. 
but when I ran these jobs .. almost everytime before the mappers are all
done the reducers start working .. so it would say map 60% reduce 30% .. how
does this works
Does it finds all possibly values for a single key from all mappers .. pass
that on the reducer and then works on other keys
any help is appreciated
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