I think the reduce can be started before all of the map finished. See the configration item in mapred-site.xml
<property> <name>mapred.reduce.slowstart.completed.maps</name> <value>0.05</value> <description>Fraction of the number of maps in the job which should be complete before reduces are scheduled for the job. </description> </property> Correct me, if I'm wrong. On Tue, Dec 21, 2010 at 4:18 AM, Harsh J <qwertyman...@gmail.com> wrote: > Hi, > > On Tue, Dec 21, 2010 at 12:03 AM, Pedro Costa <psdc1...@gmail.com> wrote: > > 1 - A reduce task should start only when a map task ends ? > Only when all map()s finish, the reduce() is called, yes. > > > > -- > > Pedro > > > > > > -- > Harsh J > www.harshj.com > -- -----李平
