MapReduce work without a cartographer

Question

This can be a very simple question, but it can be useful for many newbies like me.

Can there be a MR job without a converter? Any scenario where we need to implement this and a way to do this?

Answer 1

IdentityMapper is a cartographer that maps input directly to output.

Suppose you have an input that has a key-value format, and you have nothing to do with this at the display stage, and the only thing you would like to do is group the values ​​based on the key and perform some aggregation operation on the gearbox phase on values, you can use this converter.

Answer 2

If MapReduce does not set the Mapper class using JobConf.setMapperClass, then the default value is IdentityMapper.class.

if you do not specify a cartographer, even then there will be one map.so handler anyway, at least one handler will be launched.

http://www.fromdev.com/2010/12/interview-questions-hadoop-mapreduce.html

Answer 3

I saw MR work without Mapper, only reduced the part. Your requirement is special.

In my opinion, I think that it does not make sense for MR to work without a cartographer.