The reason why the reducer is fast upto 66% is be because of the Sorting and Shuffling phase of the reduce and when the actual task is NOT yet started.

The reduce side is divided into 3 phases of 33~% each -> shuffle (fetch data), sort and finally user-code (reduce). That is why your reduce might be faster upto 66%. In order to speed up your program you may either have to have more number of reducers or make your reducer code as optimized as possible.

Mahesh Balija,
Calsoft Labs.

On Tue, Mar 5, 2013 at 1:27 AM, Austin Chungath <> wrote:
Hi all,

I have 1 reducer and I have around 600 thousand unique keys coming to it. The total data is only around 30 mb.
My logic doesn't allow me to have more than 1 reducer.
It's taking too long to complete, around 2 hours. (till 66% it's fast then it slows down/ I don't really think it has started doing anything till 66% but then why does it show like that?). 
Are there any job execution parameters that can help improve reducer performace?
Any suggestions to improve things when we have to live with just one reducer?