To reduce system delay and overall communication load, this paper proposes an efficient algorithm BOCS (based on the change of skyline) which is out of share-nothing strategy. BOCS is to solve this issue through progressive refinement by two steps. This paper provides analytical results and they show that BOCS is optimal in terms of the communication overhead among all algorithms which are out of share-nothing strategy. Theoretical analysis and extensive experiments demonstrate that these methods are efficient, stable and scalable.