Yes this is true. Combiner may never run if intermediate values don't need to shuffle out to disk before the final output is done. Also, combiner cant be substituted as a reducer.
Sent from my iPad On Jul 10, 2011, at 4:42, Florin P <florinp...@yahoo.com> wrote: > Hello! > I've read on > http://www.fromdev.com/2010/12/interview-questions-hadoop-mapreduce.html > (cite): > "The execution of combiner is not guaranteed, Hadoop may or may not execute a > combiner. Also, if required it may execute it more then 1 times. Therefore > your MapReduce jobs should not depend on the combiners execution. " > > Is it true? Also is it possible to use the Combiner without the Reducer? The > framework will take into the consideration the Combiner in this case? > > Thank you, > > Florin
