1 research outputs found
Serving Online Requests with Mobile Servers
We study an online problem in which a set of mobile servers have to be moved
in order to efficiently serve a set of requests that arrive in an online
fashion. More formally, there is a set of nodes and a set of mobile
servers that are placed at some of the nodes. Each node can potentially host
several servers and the servers can be moved between the nodes. There are
requests that are adversarially issued at nodes one at a time. An
issued request at time needs to be served at all times . The
cost for serving the requests is a function of the number of servers and
requests at the different nodes. The requirements on how to serve the requests
are governed by two parameters and . An algorithm
needs to guarantee at all times that the total service cost remains within a
multiplicative factor of and an additive term of the current
optimal service cost. We consider online algorithms for two different
minimization objectives. We first consider the natural problem of minimizing
the total number of server movements. We show that in this case for every ,
the competitive ratio of every deterministic online algorithm needs to be at
least . Given this negative result, we then extend the minimization
objective to also include the current service cost. We give almost tight bounds
on the competitive ratio of the online problem where one needs to minimize the
sum of the total number of movements and the current service cost. In
particular, we show that at the cost of an additional additive term which is
roughly linear in , it is possible to achieve a multiplicative competitive
ratio of for every constant .Comment: 25 page