Load Sharing in Distributed Systems

An important part of a distributed system design is the choice of a load sharing or global scheduling strategy. A comprehensive literature survey on this topic is presented. We propose a taxonomy of load sharing algorithms that draws a basic dichotomy between source-initiative and server-initiative approaches. The taxonomy enables ten representative algorithms to be selected for performance evaluation. A performance metric called the Q-factor (quality of load sharing) is defined which summarizes both overall efficiency and fairness of an algorithm and allows algorithms to be ranked by performance. We then evaluate the algorithms using both mathematical and simulation techniques. The results of the study show that: i) the choice of load sharing algorithm is a critical design decision; ii) for the same level of scheduling information exchange, server-initiative has the potential of outperforming source-initiative algorithms (whether this potential is realized depends on factors such as communication overhead); iii) the Q-factor is a useful yardstick; iv) some algorithms, which have previously received little attention, e.g., multiserver cyclic service, may provide effective solutions.