MapReduce materials

https://www.youtube.com/watch?v=x-PCNX4prLA

This has good explanation for java MR

https://app.pluralsight.com/player?course=mapreduce-understanding&author=janani-ravi&name=mapreduce-understanding-m3&clip=0&mode=live

This has good info on MR related to combiner,partitioner

 Mapper

Keyin, valuein, keyoutm , valueoutm

Reducer

Keyinm, valueinm, keyout , valueout

keyoutm  will be passed to reducer as Keyinm

Valueoutm will be passed to reducer as valueinm

MRUnit can be used for doing MR testing.

https://www.youtube.com/watch?v=LADHT7t8Duk

https://www.youtube.com/watch?v=u8HarSx7glE

https://data-flair.training/blogs/how-hadoop-mapreduce-works/