Robots are deployed by a Web search engine for collecting information from
different Web servers in order to maintain the currency of its data base of
Web pages. In this paper, we investigate the number of robots to be used b
y a scorch engine so as to maximize the currency of the data base without p
utting an unnecessary load on the network. We use a queueing model to repre
sent the system. The arrivals to the queueing system are Web pages brought
by the robots; service corresponds to the indexing of these pages. The obje
ctive is to find the number of robots, and thus the arrival rate of the que
ueing system, such that the indexing queue is neither starved nor saturated
. For this, we consider a finite-buffer queueing system and define the cost
function to be minimized as a weighted sum of the loss probability and the
starvation probability. Under the assumption that arrivals form a Poisson
process, and that service times are independent and identically distributed
random variables with an exponential distribution, or with a more general
service function, we obtain explicit/numerical solutions for the optimal nu
mber of robots to deploy.