The PROMPT Real - Time Commit

| We investigate the performance implications of providing transaction atomicity for rm-deadline real-time applications operating on distributed data. Using a detailed simulation model, the real-time performance of a representative set of classical transaction commit protocols is evaluated. The experimental results show that data distribution has a signiicant innuence on real-time performance and that the choice of commit protocol clearly aaects the magnitude of this innuence. We also propose and evaluate a new commit protocol, PROMPT (Permits Reading Of Modiied Prepared-data for Timeliness), that is speciically designed for the real-time domain. PROMPT allows transactions to \optimistically" borrow, in a controlled manner, the updated data of transactions currently in their commit phase. This controlled borrowing reduces the data inaccessibility and the priority inversion that is inherent in distributed real-time commit processing. A simulation-based evaluation shows PROMPT to be highly successful, as compared to the classical commit protocols, in minimizing the number of missed transaction deadlines. In fact, its performance is close to the best on-line performance that could be achieved using the optimistic lending approach. Further, it is easy to implement and incorporate in current database system software. Finally, PROMPT is compared against an alternative priority inheritance-based approach to addressing priority inversion during commit processing. The results indicate that priority inheritance does not provide tangible performance beneets.