Map reduce flow clarification

[#1]

what is the order of execution for mapreduce Job? Is it correct and please correct me if i am wrong?

Mapper
partition each mapper output
sorting with in each partition based on key
grouping
shuffle and merge:each reducer will take one partition from all map tasks and merge together
combiner
reducer

[#2 · Accepted solution]

@vamsi valiveti

This is the right order:

[#3]

a)could you please provide source for this link and it is really useful

b)what about these two in the diagram and where it will come?

1. grouping
2. shuffle and merge:each reducer will take one partition from all map tasks and merge together

[#4]

@vamsi valiveti

a> This slide is from Hortonworks Training course. The course/slides are available to paid customers only.

b>

i> there is nothing like grouping

ii> Shuffle happens when data move from Map to reduce (please see the diagram) and Merge happens during sort phase at Reducer side.