Juhnyoung Lee

Using dynamic adjustment of serialization order for real-time database systems

Studies concluded that for a variety of reasons, optimistic concurrency control appears well-suited to real-time database systems. Especially, they showed that in a real-time database system that discards tardy transactions, optimistic concurrency control outperforms locking. We show that the optimistic algorithms used in those studies incur restarts unnecessary to ensure data consistency. We present a new optimistic concurrency control algorithm that can avoid such unnecessary restarts by adjusting serialization order dynamically, and demonstrate that the new algorithm outperforms the previous ones over a wide range of system workload. It appears that this algorithm is a promising candidate for a basic concurrency control mechanism for real-time database systems.<<ETX>>

Hybrid protocols using dynamic adjustment of serialization order for real-time concurrency control

ConclusionsTime-critical scheduling in real-time database systems has two components: real-time scheduling and concurrency control. While both concurrency control and real-time scheduling are well-developed and well-understood, there is only limited knowledge about the integration of concurrency control and real-time scheduling. Though recently the problem has been studied actively, the proposed solutions are still at an initial stage. A major source of problems in integrating the two is the lack of coordination in the development. They are developed on different objectives and incompatible assumptions (Buchmann 1989).Most of the proposed work for real-time concurrency control employ a simple method to utilize one concurrency control scheme such as 2PL, TO and OCC, and to consider the priority of operations inherited from the timing constraints of transactions in operation scheduling. This method has an inherent disadvantage of being limited by the concurrency control method used as the base. Since neither of pessimistic nor optimistic concurrency control is satisfactory by itself for real-time scheduling, this simple method using only one control can hardly satisfy the timing requirements of RTDBS. Problems such as excessive blocking, wasted restarts, and priority inversion are serious in RTDBS.In this paper, we proposed two real-time transaction scheduling protocols which employ a hybrid approach, i.e., a combination of both pessimistic and optimistic approaches. These protocols make use of a new conflict resolution scheme called dynamic adjustment of serialization order, which supports priority-driven scheduling, and avoids unnecessary aborts.

Issues in developing object-oriented database systems for real-time applications

Database systems for real-time applications must satisfy timing constraints associated with transactions, in addition to maintaining data consistency. Recently, interests in object-oriented databases have been growing for non-traditional applications of database systems, and several real-time applications are being developed using an object-oriented paradigm. The object-oriented approach seems promising for developing complex real-time database applications. However, it is not clear whether object-oriented database systems would be superior than relational database systems for supporting real-time applications. In this paper, we address issues that must be investigated in order to design and develop an object-oriented database system for real-time applications. Also, we present a model that integrates features for scheduling real-time transactions with the traditional object-oriented database model.<<ETX>>

New Paradigms for Real-Time Database Systems

Abstract Real-time database systems (RTDBS) are database systems in which transactions have timing constraints such as deadlines. Paradigms used in conventional database systems are not suitable for real-time database systems. In this paper, we present an optimistic concurrency control algorithm for real-time tran-saction scheduling and a new parallel processing paradigm for real-time database operations.

Semantic-based concurrency control for object-oriented database systems supporting real-time applications

Recently object-oriented database technology has started to gain the attention of researchers in real-time database systems. This paper investigates major issues in designing semantic-based concurrency control for object-orient database systems supporting real-time applications, and describes an approach to solving those problems in an efficient way. This approach depends on the notion of affected-set of operations to determine operation compatibilities, and employs concurrency control algorithms augmented with priority-based conflict resolution schemes. With this method, it is impossible to manoeuvre the trade-off between logical and temporal consistency constraints in determining operation compatibilities, because the method deals with the two separately in different dimensions. However, this approach significantly lessens the complexity of the compatibility relation construction process, and can easily apply results from previous research on semantic-based concurrency control for object-oriented databases and on priority-based concurrency control for real-time database systems.<<ETX>>

Real-time transaction processing: pessimistic, optimistic, and hybrid approaches

A real-time database system (RTDBS) differs from a conventional database system because in addition to the consistency constraints of the database, timing constraints of individual transaction need to be satisfied. To provide real-time response for queries and update while maintaining the consistency of data, real-time concurrency control should involve efficient integration of the ideas from both database concurrency control and real-time scheduling. The authors proposed hybrid real-time concurrency control protocols which combine pessimistic and optimistic approaches to concurrency control in order to control blocking and aborting in a more effective manner.<<ETX>>

A New Approach To Real-time Transaction

A real-time database system differs from a conventional database system because in addition to the consistency constraints of the database, timing constraints of individual transaction need to be satisfied. Various real-time transaction scheduling algorithms have been proposed which employ either a pessimistic or an optimistic approach to concurrency control. Here, we present new real-time transaction scheduling algorithms which employ a hybrid approach, i.e., a combination of both pessimistic and optimistic approaches. These protocols make use of a new conflict resolution scheme called dynamic adjustment of serialization order, which supports priority-driven scheduling, and avoids unnecessary aborts. Our experimental results indicate that hybrid protocols outperform other real-time concurrency control protocols in certain performance metrics.