Alternative and compensation are not only two basic characteristics of the real-time transaction but also the body of the concurrency control. At the same time, new problems are brought. AC-Based OCC-FV protocol associates alternative and compensation with optimistic concurrency control protocol OCC-FV. For each transaction in accepted queue, an alternative which causes no conflict can be chosen to join the ready queue as soon as possible. This is just a kind of ideal circumstance. If the conflict is inevitable, it is necessary to choose a suitable alternative to join the concurrency control, but also ensures the system to be in a safe state when conflicts take place. In conflict resolution, the optimistic concurrency control protocol OCC-FV is extended in combination with the compensation characteristic, when the transaction failed, immediate dispatch of corresponding compensation transactions is taken to prevent the system from disaster.
Comparing two-phase locking and optimistic concurrency control protocols in multiprocessor real-time databases
