Thrashing in two-phase locking revisited

Abstract

The fraction of blocked transactions (β) and the conflict rate, the ratio of locks held by all and active transactions, have been proposed as parameters to be monitored for load control. This study investigates the robustness of these parameters in the case of transactions requesting a variable number of locks and different processing times for transaction steps. Simulation results show that β and the fraction of lock conflicts with blocked transactions ρ both vary in a rather narrow range as transaction parameters are varied. The fact that ρ is a key parameter and is suitable for implementing load control is demonstrated by developing an analytic solution method which utilizes it in an equation. Validation results show that this method is quite accurate and outperforms an earlier solution method based on two levels of transaction blocking.