On coupling many small systems for transaction processing

Abstract

The prospect of coupling a large number of small inexpensive microprocessor based systems to deliver the performance of a large transaction processing system at lower cost has not been realized, to date. Inter-system interference, multi-system coupling protocol overhead and the increased processing time for smaller systems can cause considerable degradation. A methodology is developed to determine the number of processors needed to satisfy transaction throughput and response time requirements for processors of different MIPS (sizes). The minimum MIPS per processor required to satisfy response time, throughput and utilization constraints in a transaction processing complex of N coupled systems is also determined, by using an approximate analytical model driven by measured workload parameters. Despite large assumed cost advantages on a per MIPS basis we find that small systems do not match up to the cost/performance of some larger systems. Besides multi-system's coupling degradation, there is a small system effect. Because of the increased transaction execution time in smaller systems, transactions hold on to resources longer, thereby causing increased inter-system interference. Our cost criterion indicates that there is an optimum processor size below which total system costs would increase appreciably. Ways to reduce the inter-system interference and coupling protocol overheads are investigated and shown to shift this optimum.