摘要：Control Concurrency on RTDBS more complex than in conventional database system. Besides guarantee database consistency, on RTDBS control concurrency can support transaction deadlines. Mean while validities and value of data item change depend on time. Conventional control concurrency algorithm can be divided to two groups: Pessimistic Concurrency Control (PCC) and Optimistic Concurrency Control (OCC). PCC prevent conflict between transactions executed while OCC overcome between transactions after that transaction executed that restarted in conflict happened. These algorithms have weakness if applied in RTDBS that gives tight time on transaction execution because as a parameter is number of transactions done before deadlines, not only number of concurrency maximum and throughput. To overcome those two algorithms weakness some researches done. Between results modifications is speculative concurrency control and Hybrid concurrency control for the Nested model. But between alternatives there are some weaknesses, so it needs development for better control concurrency for RTDBS.
