Paper detail

Dynamics of the supermarket model

We consider the long term behaviour of a Markov chain ξ(t) on \Z^N based on the N station supermarket model. Different routing policies for the supermarket model give different Markov chains. We show that for a general class of local routing policies, "join the least weighted queue" (JLW), the N one-dimensional components ξ_i(t) can be partitioned into disjoint clusters C_k. Within each cluster C_k the "speed" of each component ξ_j converges to a constant V_k and under certain conditions ξis recurrent in shape on each cluster. To establish these results we have assembled methods from two distinct areas of mathematics, semi-martingale techniques used for showing stability of Markov chains together with the theory of optimal flows in networks. As corollaries to our main result we obtain the stability classification of the supermarket model under any JLW policy and can explicitly compute the C_k and V_k for any instance of the model and specific JLW policy.