The Research Of Concurrency Control Mechanism For Distributed Real-Time Transactions In Mobile Broadcast Environments

The research in mobile distributed real-time database systems (MDRTDBSs) is receiving growing attention due to a large number of potential mobile computing applications,such as real-time traffic monitoring systems and mobile stock.With the rapid development of different kinds of networks,mobile computing technology leads to a true mutation in the use,design and development of future information systems.Mobile Computing technology is all through very important research topic in area of computer notwork and communication.Thus,the research of mobile computing technology in theory and application has very important theoretical and practical significance.Mobile computing environments are distributed dynamicly running environments.The communication bandwidth is asymmetric.The bandwidth from mobile hosts(MHs) to the server is very limited. Communication capacity from the server to MHs is relatively much greater than from MHs to the server.Owing to limited wireless bandwidth and frequent disconnections,traditional concurrency control protocols do not suit for mobile broadcast environment.Broadcast data has become a widely accepted approach of communication in MDRTDBSs.Now mobile distributed real-time transaction processing is very important research direction of mobile computing theory and application in mobile broadcast environments.The concurrency control mechanism is crucial technology in MDRTDBSs.Therefor,the thesis studies thoroughly concurrency control mechanism for distributed real-time transactions in mobile broadcast environments.The main contributions are as follows:1.MV-IR-VIN(Multiversion-Invalidation Report-Validation Information) is presented.We introduce multiversion structure of broadcast channel.At the beginning of every broadcast cycle,the server broadcasts validation information(VIN) of committed transactions in the last broadcast cycle.The MHs perform local pre-validation for mobile real-time transactions by receiving VIN.2.The multiversion dynamic adjustment of serialization order is presented.The cost of mobile transaction restart is very high.The main purpose of multiversion dynamic adjustment of serialization order of transactions at validation is to prevent unnecessary transaction restarts. There is not write-write conflict in multiversion mechanism because transactions write data items on different versions.3.The multiversion two-phase validation is presented.At the MHs, all mobile transactions have to perform a local pre-validation. Transactions that survive in local pre-validation must be submitted to the server for local final validation.Such an early data conflict detection feature can save processing and communication resources.4.A three-tier commit structure is also proposed,which can guarantee the atomicity of the mobile distributed real-time transactions. In bottom layer,a mobile read-only transaction at MH can be committed if it passes all the local pre-validation in course of its execution.Respond time of mobile read-only transactions is greatly improved.In middle layer, if mobile update transactions can pass final local validation,they can be committed locally.In top layer,mobile distributed transactions are needed a global validation for distributed serializability.5.DMVOCC-MDA-2LPV(Distributed Multiversion Optimistic Concurrency Control with Multiversion Dynamic Adjustment using Two-Phase Local Validation) protocol is designed for processing mobile distributed real-time transactions in mobile broadcast environments.At the MHs,all mobile transactions perform local pre-validation of transactions by using backward validation mechanism.The local pre-validation process is carried out against committed transactions at the server in the last broadcast cycle.Transactions that survive in local pre-validation must be submitted to the server for local final validation. The new protocol can eliminate conflicts between mobile read-only and mobile update transactions,and resolve data conflicts flexibly using multiversion dynamic adjustment of serialization order to avoid unnecessary restarts of transactions.Mobile read-only transactions can be committed with no-blocking,and respond time of mobile read-only transactions is greatly reduced.The tolerance of mobile transactions of disconnections from the broadcast channel is increased.6.The correctness of the concurrency control protocol presented, DMVOCC-MDA-2PLV,is proved.A series of extensive simulation experiments have been performed to evaluate the performance of the new protocol.The simulation results show that the concurrency control protocol proposed offers better performance than other protocols in terms of miss rate,restart rate,commit rate.Under high system load and high disconnection,DMVOCC-MDA-2PLV protocol is also offers better performance than other protocols.The research in the thesis provides a theoretical and practical solution for implementing concurrency control in MDRTDBSs.