1. An article of manufacture comprising a non-transitory computer readable storage medium having computer readable instructions tangibly embodied thereon which, when implemented, cause a computer to carry out a plurality of method steps comprising: partitioning a cluster into multiple computational groups; determining at least one key-group leader within each of the multiple computational groups; performing a first combine operation at each of the multiple computational groups; performing a second combine operation at each of the at least one key-group leader within each of the multiple computational groups based on a result from the first combine operation; and performing asynchronous global map-reduce operations across each of the at least one key-group leader within each of the multiple computational groups via performing a Steiner tree-based reduce operation across each of the at least one key-group leader within each of the multiple computational groups, wherein said Steiner tree-based reduce operation comprises using a distributed Steiner tree per key-group.