Re:what's the mechnism to determine the reducer number and reduce progress

[原攀峰 <yp...@163.com>]

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" <le...@gmail.com> 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