2019/02/01 by Anastasia Koloskova, Koloskova, Anastasia, Sebastian U. Stich +3 · 88 citations
Computer Science · Mathematics · #Distributed Control Multi-Agent Systems #Privacy-Preserving Technologies in Data #Stochastic Gradient Optimization Techniques #acm:68W10 #acm:68W15 #acm:68W40 #acm:90C06 #acm:90C25 #acm:90C35 #cs.DC #cs.DS #cs.LG #math.OC #msc:68W10 #msc:68W15 #msc:68W40 #msc:90C06 #msc:90C25 #msc:90C35 #stat.ML
paper · pdf · doi:10.48550/arxiv.1902.00340
arxiv created 2019/02/01 · arxiv updated 2019/02/04
We consider decentralized stochastic optimization with the objective function (e.g. data samples for machine learning task) being distributed over n machines that can only communicate to their neighbors on a fixed communication graph. To reduce the communication bottleneck, the nodes compress (e.g. quantize or sparsify) their model updates. We cover both unbiased and biased compression operators with quality denoted by ω≤ 1 (ω=1 meaning no compression). We (i) propose a novel gossip-based stochastic gradient descent algorithm, CHOCO-SGD, that converges at rate O(1/(nT) + 1/(T δ2 ω)2) for strongly convex objectives, where T denotes the number of iterations and δ the eigengap of the connectivity matrix. Despite compression quality and network connectivity affecting the higher order terms, the first term in the rate, O(1/(nT)), is the same as for the centralized baseline with exact communication. We (ii) present a novel gossip algorithm, CHOCO-GOSSIP, for the average consensus problem that converges in time O(1/(δ2ω) log (1/ε)) for accuracy ε> 0. This is (up to our knowledge) the first gossip algorithm that supports arbitrary compressed messages for ω> 0 and still exhibits linear convergence. We (iii) show in experiments that both of our algorithms do outperform the respective state-of-the-art baselines and CHOCO-SGD can reduce communication by at least two orders of magnitudes.