CIRS: A State-Conscious Concurrency Control Protocol for Replicated Real-Time Databases Vishal Pathak M.M.M.Engg.College Gorakhpur, India Ajay Pratap M.M.M.Engg.College Gorakhpur, India Rabin Kr. Singh M.M.M.Engg.College Gorakhpur, India Abhishek Kr. Singh M.M.M.Engg.College Gorakhpur, India Abstract—Replication [5] is the technique of using multiple copies of a server or a resource for better availability and performance.Each copy is called a replica. The main goal of replication is to improve availability, since a service is available even if some of its replicas are not. This helps mission critical services, such as many financial systems or reservation systems, where even a short outage can be very disruptive and expensive.A prerequisite for realizing the banefits of replication, however, is the devlopement of high performance concurrency machenism. Current applications, such as Web-based services, electronic commerce, mobile telecommunication system, etc., are distributed in nature and manipulate time-critical databases. In order to enhance the performance and the availability of such applications, one of the main techniques is to replicate data on multiple sites of the network. Therefore, the major issue is to develop efficient replica concurrency control protocols that are able to tolerate the overload of the distributed system. In fact, if the system is not designed to handle overloads, the effects can be catastrophic and some primordial transactions of the application can miss their deadlines. In this paper we present CIRS (Concurrency control In Replicated realtime Systems) a state conscious concurrency control protocol in replicated distributed environment which is specially for firm realtime database system. CIRS mechanism uses S2PL (Static Two Phase Locking) for deadlock free environment. It also includes veto power given to a cohort after receiving PREPARE message from its coordinator. Also with some more assumptions like sending an extra message in execution phase but after completion of execution at local copy which is described later in this paper the proposed mechanism has a significant increased performance over O2PL and MIRROR in decreasing execution time of the current transaction and it also decreases the waiting time of transactions in wait queue. I. INTRODUCTION Distributed real time database systems (DRTDBSs) can be defined as database systems that support real time transactions. A distributed database is a single logical database that is spread physically across computers in multiple locations that are connected by a data communications network. The network must allow the users to share the data i.e. user at location A must be able to access the data at location B. 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. Transactions 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 paper reports efficient solutions for some of the issues important to the performance of replicated firm deadline based DRTDBS. The performance of DRTDBS depends on several factors such as specification of transaction’s deadline, priority assignment policy, scheduling transactions with deadlines, time cognizant 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. On possible goal of replication is to have replicas behave functionally like nonreplicated servers. This goal can be stated precisely by the concept of one-copy serializability, which extends the concept of serializability to a system where multiple replicas are present. An execution is one-copy serializable if it has the same effect as a Vishal Pathak et al. / International Journal on Computer Science and Engineering (IJCSE) ISSN : 0975-3397 Vol. 3 No. 1 Jan 2011 430