Resolving executing-committing conflict in distributed real-time database systems
Student thesis: Master's Thesis
Related Research Unit(s)
In a distributed real-time database system (DRTDBS), the interaction of transactions and failure atomicity are handled by concurrency and commitment control protocol separately. When there is a conflict between the system concurrency and failure atomicity, system concurrency is always given way to the failure atomicity. Because of this, executing transactions are usually blocked whenever they conflict with committing transactions - the executing-committing conflict. However, blocking the executing transactions is unnecessary most of the time and this approach adversely affects the performance of a system. Yet, the significance of the executing-committing conflict has long been neglected. In this thesis, a new protocol called Deadline-driven Conflict Resolution (DDCR) protocol is proposed. This protocol integrates concurrency control and commitment management to resolve executing-committing conflict in a DRTDBS. With the DDCR, higher degree of concurrency can be achieved since the number of data conflicts, not just the executing-committing conflict, are reduced. Data objects that are held by committing transactions can now be shared with executing transactions. Also, the impact of temporary failure, which occurred during the commitment stage of a transaction, is alleviated because the dependency among transactions can be reversed. In this thesis, a simulation model has been developed and extensive experiments have been performed to compare the performance of the DDCR with other protocols such as the OPT , the Healthy-OPT  and the Base protocol. The simulation results show that the DDCR can significantly improve the performance of a system under various workloads and distributions. Its performance is consistently better than the Base protocol and the OPT protocols in both the main-memory and disk resident DRTDBS. Finally, the DDCR is modified to include a different notion of serializability and is applied to a mixed transaction DRTDBS. It shows that the DDCR protocol can be easily modified to deal with different working environment and further improves system performance.
- Transaction systems (Computer systems), Database management