Data sharing in Hadoop Map Reduce chaining

Question

Is it possible to share a value between successive reducer and mapper?

Or is it possible to store the output of first reducer into memory and second mapper can acces

Answer 1

If number of distinct rows produced by Reducer1 is small (say you have 10000 (id,price) tuples), using two stage processing is preferred. You can load results from first map/reduce into memory in each Map2 mapper and filter input data. So, no uneeded data will be transferred via network and all data will be processed locally. With use of combineres amount of data can be even less.

In case of huge amount of distinct rows looks like you need to read data twice.