| The rapid development of mobile computing technology provides a new platform for the application of distributed real-time database systems. With the popularity of portable computer, the application of mobile real-time database becomes more and more common. We call this new system "mobile distributed real-time database systems" (MDRTDBS).The processing of time-limited transaction in such a system is a brand new question, and many problems have not been solved yet.As a distributed real-time database system in mobile environment, a MDRTDBS must not only face the difficulties of distributed real-time database systems, but also the many problems caused by mobile environment. In real-time database systems, transactions must both satisfied the equality between different data items and deadlines. Many concurrency protocols have been designed to handle these problems. On the other hand, the wireless network of a MDRTDBS is quite uncertain. Its wireless band and the processing ability of its mobile clients are limited. All these characters pose great challenges to a MDRTDBS. Now, though there are many concurrency control protocols for real-time database systems and mobile database systems separately,the number of concurrency control protocols for MDRTDBS is very small. The research in such area is just at the beginning.This paper first describes the ACID characters of transaction, Then according to these characters, it analyzes all kinds of lock-based protocols, time-stamp ordering protocols and optimistic protocols, points out their performance in solving dead-lock,ensuring the serializability and recoverability of concurrently executed transactions.Then it analyzes thetime-stamp ordering concurrency control protocols in real-time database systems, explains their advantages and disadvantages in a mobile environment, and an optimized protocol is offered after that. Finally , a new time-stamp ordering protocol is proposed for MDRTDBS, and its performance is analyzed. |
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