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Hadoop >> mail # user >> Is combiner and map in same JVM?

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Is combiner and map in same JVM?
Suppose I have a Hadoop job and have set my combiner to the Reducer class.
Does the map function and the combiner function run in the same JVM in
different threads? or in different JVMs?
I ask because I have to load a native library and if they are in the same
JVM then the native library is loaded once and I have to take  precautions.

Thank you
Saptarshi Guha