The wiki (or Hadoop The Definitive Guide) are good ressources.
https://www.inkling.com/read/hadoop-definitive-guide-tom-white-3rd/chapter-7/input-formats

Mapper is the name of the abstract class/interface. It does not really make
sense to talk about number of mappers.
A task is a jvm that can be launched only if there is a free slot ie for a
given slot, at a given time, there will be at maximum only a single task.
During the task, the configured Mapper will be instantiated.

Always :
Number of input splits = no. of map tasks

And generally :
number of hdfs blocks = number of input splits

Regards

Bertrand

PS : I don't know if it is only my client, but avoid red when writting a
mail.

On Tue, Feb 25, 2014 at 8:49 AM, Dieter De Witte <[EMAIL PROTECTED]> wrote:
 
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