More Effective Distributed ML via a Stale Synchronous Parallel Parameter Server †Qirong Ho, †James Cipar, §Henggang Cui, †Jin Kyu Kim, †Seunghak Lee, ‡Phillip B. Gibbons, †Garth A. Gibson, §Gregory R. Ganger, †Eric P. Xing †School of Computer Science Carnegie Mellon University Pittsburgh, PA 15213 qho@, jcipar@, jinkyuk@, seunghak@, garth@, epxing@cs.cmu.edu §Electrical and Computer Engineering C