I have used a similar explanation using fields of wheat, combine harvesters and grain trucks.
The combine harvesters are performing a Map - they do the heavy work and actually modify the contents of the fields. The more combines you have the quicker the job gets done.
The reduce step is the trucks that collect the grain and combine it into one pile (back at the silo).
I like this analogy as it shows that some natural jobs are linearly divisible as they need no synchronisation between workers while others are more complicated due to needing to combine results.
Each combine has no need to synchronise with the others - it can be told which fields to harvest and be left to do it.
During the grain collection you can have many trucks but it soon becomes clear that there are loads of ways to organise them depending on the size of the trucks, fields and the distance to the depot. Trucks could combine loads in the fields before returning to the grain silo. There is always a danger that one truck might be left waiting for another.
This analogy also allows us to discuss whether we need to wait for all grain to be harvested before we send out the trucks and start to gather it in and whether we need the same number of trucks as combine harvesters.
The combine harvesters are performing a Map - they do the heavy work and actually modify the contents of the fields. The more combines you have the quicker the job gets done.
The reduce step is the trucks that collect the grain and combine it into one pile (back at the silo).
I like this analogy as it shows that some natural jobs are linearly divisible as they need no synchronisation between workers while others are more complicated due to needing to combine results.
Each combine has no need to synchronise with the others - it can be told which fields to harvest and be left to do it.
During the grain collection you can have many trucks but it soon becomes clear that there are loads of ways to organise them depending on the size of the trucks, fields and the distance to the depot. Trucks could combine loads in the fields before returning to the grain silo. There is always a danger that one truck might be left waiting for another.
This analogy also allows us to discuss whether we need to wait for all grain to be harvested before we send out the trucks and start to gather it in and whether we need the same number of trucks as combine harvesters.