Real Time Data Base System

Abstract

Distributed real time database systems (DRTDBSs) can be defined as database systems that support real time transactions. They are used for a wide spectrum of applications such as air traffic control, stock market trading, banking, telemedicine etc. In DRTDBS, there are two types of transactions: global and local. The global transactions are distributed real-time transaction executed at more than one site whereas the local transactions are executed at generating site only. A commonly model used for distributed real time transaction consists of a process, called coordinator, which is executed at the site where the transaction is submitted, and a collection of other processes called cohorts executing at various sites where the required data items reside. newlineTransactions in a real time database are classified into three types, viz. hard, soft and firm. The classification is based on how the application is affected by the violation of transaction time constraints. This thesis reports efficient solutions for some of the issues important to the performance of firm deadline based DRTDBS. newlineThe performance of DRTDBS depends on several factors such as specification of transaction s deadline, priority assignment policy, scheduling transactions with deadlines, time aware buffer and locks management, commit procedure etc. One of the primary performance determinants is the policy used to schedule transactions for the system resources. The resources that are typically scheduled are processors, main memory, disks and the data items stored in database. newlineIn order to resolve the contention for these resources, DRTDBSs have to establish a priority ordering among the cohorts. This ordering should minimize the percentage of missed transactions which is the primary performance metric, defined as percentage of input transactions that the system is unable to complete before their deadlines. We proposed a scheme where the priority of each cohort is determined independently on the basis of the locks required by it at its execution site.