Department of Computer Science and Engineering, Fudan University, Shanghai, China/ Institute of Massive Computing, East China Normal University, Shanghai, China. ayzhou@fudan.edu.c;Department of Computer Science and Engineering, Fudan University, Shanghai, China. rongzh@fudan.edu.cn;Singapore MIT Alliance, National University of Singapore, Singapore. hieuvq@nus.edu.sg;Institute of Massive Computing, East China Normal University, Shanghai, China. wnqian@sei.ecnu.edu.cn