Lunedì 21 Novembre 2016 dalle ore 16:30 alle 18:30, nell’aula C2A al piano terra DIETI, il Prof. Peter Popov della City University London, in un visiting period presso il Dependable Systems and Software Engineering Research Team (DESSERT) al DIETI, terrà – nell’ambito del corso di Sistemi Distribuiti del Corso di Laurea Magistrale in Ingegneria Informatica - il seminario: Software Design Diversity from Conceptual Models to Practical Implementations.



Performance is often the most important non-functional property for database systems and associated replication solutions. This is true at least in industrial contexts. Evaluating performance using real systems, however, is computationally demanding and costly. In many cases, choosing between several competing replication protocols poses a difficulty in ranking these protocols meaningfully: the ranking is determined not so much by the quality of the competing protocols but, instead, by the quality of the available implementations. Addressing this difficulty requires a level of abstraction in which the impact on the comparison of the implementations is reduced, or entirely eliminated. We propose a stochastic model for performance evaluation of database replication protocols, paying particular attention to: - empirical validation of a number of assumptions used in the stochastic model, and - empirical validation of model accuracy for a chosen replication protocol. The accuracy estimation is based on the entire probability distribution of transaction times, not on simple statistics such as mean response time, which is commonly used. For the empirical validations we used the TPC-C benchmark. Our implementation of the model is based on Stochastic Activity Networks (SAN), extended by bespoke code. The model may reduce the cost of performance evaluation in comparison with empirical measurements, while keeping the accuracy of the assessment to an acceptable level.

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