Analytical modelling of a hierarchical buffer for a data sharing environment

In a data sharing environment, where a number of loosely coupled computing nodes share a common storage subsystem, the effectiveness of a private buffer at each node is limited due to the multi-system invalidation effect, particularly under a non-uniform data access pattern. A global shared buffer can be introduced to alleviate this problem either as a disk cache or shared memory. In this paper we developed an approximate analytic model to evaluate different shared buffer management policies (SBMPs) which differ in their choice of data granules to be put into the shared buffer. The analytic model can be used to study the trade-offs of different SBMPs and the impact of different buffer allocations between shared and private buffers. The effects of various parameters, such as, the probability of update, the number of nodes, the sizes of private and shared buffer, etc., on the performance of SBMPS are captured in the analytic model. A detailed simulation model is also developed to validate the analytic model. We show that dependency between the contents of the private and shared buffers can play an important role in determining the effectiveness of the shared buffer particularly for a small number of nodes.