TAMUNA: Accelerated Federated Learning with Local Training and Partial Participation

In federated learning, a large number of users are involved in a global learning task, in a collaborative way. They alternate local computations and communication with a distant server. Communication, which can be slow and costly, is the main bottleneck in this setting. To accelerate distributed gradient descent, the popular strategy of local training is to communicate less frequently; that is, to perform several iterations of local computations between the communication steps. A recent breakthrough in this field was made by Mishchenko et al. (2022): their Scaffnew algorithm is the first to probably benefit from local training, with accelerated communication complexity. However, it was an open and challenging question to know whether the powerful mechanism behind Scaffnew would be compatible with partial participation, the desirable feature that not all clients need to participate to every round of the training process. We answer this question positively and propose a new algorithm, which handles local training and partial participation, with state-of-the-art communication complexity.