实时Client/Server数据库多版本两个阶段封锁并发控制协议

提出了实时Client／Server数据库多版本两阶段封锁并发控制协议．该协议具有多版本并发控制机制与两阶段封锁机制的优点，使用如下策略以减少延误截止时间事务数量：若冲突集中有比持锁事务Ti优先级高的事务，且Ti重启动不会延误截止时间，则Ti重启动，冲突集中优先级最高的事务获得锁；否则，冲突集中其它事务等待．为了提高只读事务的响应时间，客户端设有一致数据库影子，只读事务在客户端处理．通过仿真模拟，与2V2PL和OCC—TI—WAIT—50协议进行比较，结果表明：该并发控制协议不仅能有效降低事务延误截止时间率，而且能改善只读事务的响应时间，减少优先级高事务的锁等待时间．协议性能优于2V2PL协议和OCC—TI—WAIT—50协议．

Multiversion Two-Phase Locking Concurrency Control Protocol in Real-Time Client /Server Database Systems

The article presents multiversion two-phase locking concurrency control protocol in real-time client/server database systems. The scheme attempts to combine the advantages of multiversion concurrency control mechanism with the advantages of two-phase locking mechanism. The protocol uses strategies to reduce the number of transactions that would miss their deadlines. When conflicting set includes higher priority transactions than transaction T i that holds lock and T i would not miss its deadlines, if restarted, the protocol restarts T i and the transactions with highest priority in conflicting set holds lock. In other cases, transactions in conflicting set wait.To boost the response time of read-only transactions, the protocol associate each client-side with a consistent database image and processes read-only transactions in client-side. The protocol presented is compared with 2V2PL protocol and OCC-TI-WAIT-50 protocol by simulation experiments. The experiments show that the protocol can not only effectively reduce miss rate of transaction, but also significantly improve the response time of client-side read-only transactions and the blocking time of higher-priority.