Lock-based Concurrency Control Research Articles

Lock-Based Concurrency Control in Distributed Real-Time Database Systems

A real-time database system (RTDBS) is designed to provide timely response to the transactions of data-intensive applications. The transactions processed in a RTDBS are associated with real-time constraints typically in the form of deadlines. With the current database technology it is extremely difficult to provide schedules guaranteeing transaction deadlines. This difficulty comes from the unpredictability of transaction response times. Efficient resource scheduling algorithms and concurrency control protocols are required to schedule RTDB transactions so as to maximize the number of satisfied deadlines. In this paper, we describe several distributed, lock-based, real-time concurrency control protocols and report on the relative performance of the protocols in a distributed database environment. The protocols are different in the way real-time constraints of transactions are involved in controlling concurrent accesses to shared data. A detailed performance model of a distributed RTDBS was employed in the evaluation of concurrency control protocols.

Performance evaluation of cautious waiting

We study a deadlock-free locking-based concurrency control algorithm, called cautious waiting , which allows for a limited form of waiting. The algorithm is very simple to implement. We present an analytical solution to its performance evaluation based on the mean-value approach proposed by Tay et al. [18]. From the modeling point of view, we are able to do away with a major assumption used in Tay's previous work, and therefore capture more accurately both the restart and the blocking rates in the system. We show that to solve for this model we only need to solve for the root of a polynomial. The analytical tools developed enable us to see that the cautious waiting algorithm manages to achieve a delicate balance between restart and blocking, and therefore is superior (i.e., has higher throughput to both the no-waiting (i.e., immediate restart) and the general waiting algorithms under a wide range of system parameters. The study substantiates the argument that balancing restart and blocking is important in locking systems.

A new methodology to evaluate locking protocols

The average lock range (ALR) is proposed as an evaluation factor for measuring the strengths and weaknesses of locking-based concurrency control methods, for both structural and nonstructural locking. The methodology provides a simple and general way to analyze the performance of any locking method, and requires no queueing model. Based on the concept of the ALR, two popular locking protocols, the 2PL protocol and the tree protocol, are analyzed and a simulation is done to validate the correctness of the ALR model.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>