For a reduce task, the execution is divided into three phases, each of which accounts for 1/3 of the score: • The copy phase, when the task fetches map outputs. • The sort phase, when map outputs are sorted by key. • The reduce phase, when a user-defined function is applied to the list of map outputs with each key.
在2010-05-17 09:44:38，"stan lee" <[email protected]> 写道： >When I run the sort job, I found when there are 70 reduce tasks running and >no one completed, the progress bar shows that it has finished about 80%, so >how the mapreduce mechnism to caculate this? > >Also, when I run a job, as we know, we can determine the number of total >reduce tasks through setNumReduceTasks() function, but how to determine the >reducer number(I mean the tasktracker number which run the reduce task) >being used? > >Thanks! >Stan. Lee
