I hope i understood what you are asking is this . If not then pardon me :) from the hadoop developer handbook few lines
The*Partitioner* class determines which partition a given (key, value) pair will go to. The default partitioner computes a hash value for the key and assigns the partition based on this result. It garantees that all the records mapping to one key go to same reducer You can write your custom partitioner as well here is the link : http://developer.yahoo.com/hadoop/tutorial/module5.html#partitioning On Wed, Apr 10, 2013 at 6:19 PM, Jean-Marc Spaggiari < jean-m...@spaggiari.org> wrote: > Hi, > > quick question. How are the data from the map tasks partitionned for > the reducers? > > If there is 1 reducer, it's easy, but if there is more, are all they > same keys garanteed to end on the same reducer? Or not necessary? If > they are not, how can we provide a partionning function? > > Thanks, > > JM > -- Nitin Pawar
