Hadoop Mapreduce

• What happens if the value list for 1 key is largerfor 1 reduce task?
  • Before reduce, framework will sort it first. It should be able to be processed in memory. Otherwise, External Sorting is needed. To avoid this, more machines for reduce task should be added.
  • So it may only happen during very extreme cases when values for one key is very large
• How to deploy a map-reduce job on Hadoop?