Large transaction-processing applications, such as banking, flight reservations, telecommunications, and networking, demand increasingly high throughput and fast response times. Coupling multiple systems for database transaction processing can provide these systems with higher capacity and availability at a lower cost. Data sharing is one promising architecture for such an environment.This monograph develops a comprehensive model for analyzing the design and performance of a complex data-sharing environment that consists of multiple, loosely coupled transaction-processing nodes with a common database at the disk level. By capturing the salient features of this data sharing architecture database buffers at each node with their buffer management policies, concurrency control, buffer coherency, nonuniform database access, and CPU queueing delay - the model can be used to answer a number of design questions about scalability, buffer utilization, skewed access, policy selection, and optimal system configuration. Included are two new submodels, for private and shared buffers.Asit Dan is a Research Staff Member at the IBM T. J. Watson Research Center.