A 3+Omega(1) Lower Bound for Page Migration

We address the page migration problem, one of the most classical online problems. In this problem, we are given online requests from nodes on a network for accessing a single page, a data set stored in a node, and asked to determine a node for the page to be stored after each request. Serving a request costs the distance between the request and the page at the point of the request, and migrating the page costs the migration distance multiplied by the page size. The objective is to minimize the total sum of the service and migration costs. This problem is motivated by efficient cache management on multiprocessor systems. In this paper, we prove that no deterministic online page migration algorithm is (3+o(1))-competitive, where o-notation is with respect to the page size. Our lower bound first breaks the barrier of 3 by an additive constant for arbitrarily large page size, and disproves Black and Sleator's conjecture even in the asymptotic sense.