ShadowSync: Performing Synchronization in the Background for Highly Scalable Distributed Training. - Qinqing Zheng; Bor-Yiing Su; Jiyan Yang; Alisson G. Azzolini; Qiang Wu; Ou Jin; Shri Karandikar; Hagay Lupesko; Liang Xiong; Eric Zhou (CoRR, 2020)