A pre-emptive transaction scheduling protocol for controlling priority inversion

Hard real-time database systems (RTDBS) must provide a guarantee that real-time transactions meet their deadlines. To preserve data consistency, hard RTDBS require concurrency control protocols to synchronize transactions to access the shared data. Transaction blocking enforced by concurrency control protocols leads to the priority inversion problem that violates the principle of priority-based scheduling and degrades system schedulability. Moreover, this blocking delay due to priority inversion can be unbounded, which is unacceptable in hard real-time applications. Some priority ceiling protocols have been proposed to control priority inversion. However, they suffer from the problem of unnecessary transaction blockings due to their conservatism of scheduling transactions to access the shared data. We propose a new transaction scheduling protocol that exploits the semantics of transaction operations to enhance transaction preemptability. It can avoid some unnecessary transaction blockings and provide better worst-case scheduling conditions for a transaction set compared to other protocols.