Title: Accumulated Gradient Normalization,
Abstract: This work addresses the instability in asynchronous data parallel
optimization. It does so by introducing a novel distributed optimizer which is
able to efficiently optimize a centralized model under communication
constraints. The optimizer achieves this by pushing a normalized sequence of
first-order gradients to a parameter server. This implies that the magnitude of
a worker delta is smaller compared to an accumulated gradient, and provides a
better direction towards a minimum compared to first-order gradients, which in
turn also forces possible implicit momentum fluctuations to be more aligned
since we make the assumption that all workers contribute towards a single
minima. As a result, our approach mitigates the parameter staleness problem
more effectively since staleness in asynchrony induces (implicit) momentum, and
achieves a better convergence rate compared to other optimizers such as
asynchronous EASGD and DynSGD, which we show empirically.