hi harsh, Thanks for the reply.I get your first and second points and coming to third point how is it specific to a job? My question was specific to job.
Regards Abhishek On Mon, Aug 27, 2012 at 11:29 PM, Harsh J <ha...@cloudera.com> wrote: > Hi, > > On Tue, Aug 28, 2012 at 8:32 AM, Abhishek <abhishek.dod...@gmail.com> wrote: >> Hi all, >> >> I just want to know that, based on what factor map reduce framework decides >> number of reducers to launch for a job > > The framework does not auto-determine the number of reducers for a > job. That is purely user-or-client-program-supplied presently. > >> By default only one reducer will be launched for a given job is this right? >> If we explicitly does not mention number to launch via command line or >> driver class. > > Yes, by default the number of reduce tasks is configured to be one. > >> If i choose to decide number of reducers to mention explicitly, what should >> I consider.Because choosing in appropriate number of reducer hampers the >> performance. > > See http://wiki.apache.org/hadoop/HowManyMapsAndReduces > > -- > Harsh J
