Repairman models for replicated data management: a case study

Pessimistic control algorithms for replicated data permit only one partition to perform update operations at any time so as do ensure mutual exclusion of the replicated data object. Existing availability modeling and analyses of pessimistic control algorithms are constrained to either site-failure or link-failure only models, but not both, because of the large state space which needs to be considered. Moreover, the assumption of having an independent repairman for each link and each site has been made to reduce the complexity of analysis. We remove these restrictions with the help of stochastic Petri nets. In particular, we investigate the effect of repair dependency which occurs when sites and links may have do share the same repairman. Four repairman models are examined: (a) independent repairman with one repairman assigned to each link and each node; (b) dependent repairman with FIFO servicing discipline; (c) dependent repairman with linear-order servicing discipline; and (d) dependent repairman with best-first servicing discipline. Using dynamic voting as a case study, we compare and contrast the resulting availabilities due to the use of these four different repairman models and give a physical interpretation of the differences