How to pull data in the Map/Reduce functions?

Question

According to the Hadoop : The Definitive Guide.

The new API supports both a “push” and a “pull” style of iteration. In both APIs, key-value record pai

Answer 1

I posted a query @ mapreduce-user@hadoop.apache.org and got the answer.

The next key value pair can be retrieved from the context object which is passed to the map, by calling nextKeyValue() on it. So you will be able to pull the next data from it in the new API.

Is the performance of pull better than push in this scenario? Also, what are the scenarios in which the pull will be useful?