Real-time Concurrency Control Protocol Research Articles

Concurrency Control Protocol for Real-Time Database and the Analysis Base on Petri Net

In the article a new concurrency control protocol for real-time database (RTCC) is proposed. The protocol based on the traditional speculative concurrency control protocol (SCC). It dynamically establish the maximum of shadow to reasonably use the resources of system and add the quasi-commit phase to avoid many unnecessary restarting and enhance the concurrency of transaction. The theory of Petri net proof and results of experiment show that this protocol is feasible and effective , and it can meet the needs of real-time transaction. Speculative Concurrency Control is suitable especially for real-time database[1]. On the one hand, SCC is similar to PCC, to detect potentially harmful conflict as early as possible, so as to start a replacement schedule, thereby increasing the opportunities for transactions to meet time limits. On the other hand, SCC is similar to OCC, it allows the concurrency of conflict transaction and, therefore, avoids unnecessary matters that may affect the timely submission of delay. As a result, it alleviates the congestion problems and PCC restart OCC's problems, in order to better meet the transaction deadline. Based on the fact above mentioned, we propose a suitable real-time database concurrency control protocol [2,3] (RTCC: Concurrency Control protocol for Real-Time). The protocol of the SCC protocol on the traditional basis with a series of improvements can avoid a large number of unnecessary transaction restart and improve concurrency. Finally, by Petri net theory it can be proved feasible and correct.

Real-Time Concurrency Control Protocol Based on Accessing Temporal Data

After analyzing the temporal data characteristics and the effects on scheduling transaction, a real-time concurrency control protocol is proposed, which improves the performance of real-time systems by evaluating data-deadline and transactions execution time, improving transactions validation rules, and adjusting transactions committing order. Theoretical analysis and experimental results demonstrate that the new protocol reduces the transaction restarts numbers and the miss deadline percentage, and outperforms the previous ones.

An efficient secure real-time concurrency control protocol

Secure real-time databases must simultaneously satisfy two requirements in guaranteeing data security and minimizing the missing deadlines ratio of transactions. However, these two requirements can conflict with each other and achieve one requirement is to sacrifice the other. This paper presents a secure real-time concurrency control protocol based on optimistic method. The concurrency control protocol incorporates security constraints in a real-time optimistic concurrency control protocol and makes a suitable tradeoff between security and real-time requirements by introducing secure influence factor and real-time influence factor. The experimental results show the concurrency control protocol achieves data security without degrading real-time performance significantly.

On avoiding remote blocking via real-time concurrency control protocols

Locking protocols for hard-real-time systems have not generalized well from uniprocessors to multiprocessors. Bounding and reducing so-called “remote blocking” is widely recognized as an important problem for hard-real-time computing. We describe a combination of locking and versioning protocols together with a “chopping” analysis to shorten critical sections. Selective application of chopping and versioning reduces remote blocking and relaxes constraints imposed by pure locking protocols for multiprocessors. Using the same design-time information required for schedulability analysis in pure locking protocols, the integrated locking and versioning protocol can be implemented using only simple data structures with tunable bounded overheads and worst-case access times. Performance evaluation results via case studies and simulation experiments are presented that show that the protocol can improve pure locking protocols in a variety of settings. Experiments show that in some cases the number of tasks that can be guaranteed schedulability by our integrated protocol is 2.5 times more than the number of tasks that can be guaranteed schedulability by pure locking protocols.

The Impacts of Write-Through Procedures and Checkpointing on Real-Time Concurrency Control

In this paper, we study the impacts of checkpointing and write-through procedures, which are critical in maintaining database recoverability and transaction durability, on the performance of a well-known real-time concurrency control protocol, the Read/Write Priority Ceiling Protocol (RWPCP). Although RWPCP can guarantee the schedulability of real-time transactions, it could be unrecoverable, and the priority inversion problems could be unbounded, when transaction commitment is considered. In this paper, we first propose to extend RWPCP with deferred-commitment and extended-locking-period methods to resolve the problems. Then, we study the impacts of different checkpointing granularities and checkpointing methods on the proposed recoverable RWPCP. A detailed simulation study was conducted to evaluate the performance of the recoverable RWPCP with different checkpointing methods under various workloads.

Real-time concurrency control in a multiprocessor environment

Although many high-performance computer systems are now multiprocessor-based, little work has been done in real-time concurrency control of transaction executions in a multiprocessor environment. Real-time concurrency control protocols designed for uniprocessor or distributed environments may not fit the needs of multiprocessor-based real-time database systems because of a lower concurrency degree of transaction executions and a larger number of priority inversions. This paper proposes the concept of a priority cap to bound the maximum number of priority inversions in multiprocessor-based real-time database systems to meet transaction deadlines. We also explore the concept of two-version data to increase the system concurrency level and to explore the abundant computing resources of multiprocessor computer systems. The capability of the proposed methodology is evaluated in a multiprocessor real-time database system under different workloads, database sizes and processor configurations. It is shown that the benefits of the priority cap in reducing the blocking time of urgent transactions are far greater than the losses involved in committing less urgent transactions. The idea of two-version data also greatly improves the system performance because of a much higher concurrency degree in the system.

Strategies for resolving inter-class data conflicts in mixed real-time database systems

Although many efficient concurrency control protocols have been proposed for real-time database systems, they are mainly restricted for systems with a single type of real-time transactions or a mixed set of soft real-time and non-real-time transactions only. Their performance objective usually aims at the minimization of the number of missed deadlines of soft real-time transactions or to guarantee the deadline satisfaction of hard real-time transactions. So far, it is still lack of any good study on the design of concurrency control strategies for mixed real-time database systems (MRTDBS), which consist of both hard and soft real-time transactions, and together with non-real-time transactions. Due to the very different performance requirements of hard and soft real-time transactions, existing real-time concurrency control protocols may not be suitable to MRTDBS. In this paper, we propose strategies for resolving data conflicts between different types of transactions in an MRTDBS so that the performance requirements of each individual transaction type can be satisfied and, at the same time, the overall system performance can be improved. The performance of the proposed strategies is evaluated and compared with a real-time optimistic approach, which has been shown to give a better performance than the lock-based protocols for soft and firm real-time transactions.

Evaluation of concurrency control strategies for mixed soft real-time database systems

Previous research in real-time concurrency control mainly focuses on the schedulability guarantee of hard real-time transactions and the reduction of the miss rate of soft real-time transactions. Although many new database applications have significant response time requirements, not much work has been done in the joint scheduling of traditional non-real-time transactions and soft real-time transactions. In this paper, we study the concurrency control problems in mixed soft real-time database systems, in which both non-real-time and soft real-time transactions exist simultaneously. The objectives are to identify the cost and the performance tradeoff in the design of cost-effective and practical real-time concurrency control protocols, and to evaluate their performance under different real-time and non-real-time supports. In particular, we are interested in studying the impacts of different scheduling approaches for soft real-time transactions on the performance of non-real-time transactions. Instead of proposing yet another completely new real-time concurrency control protocol, our objective is to design an efficient integrated concurrency control method based on existing techniques. We propose several methods to integrate the well-known two phase locking and optimistic concurrency control with the aims to meet the deadline requirements of soft real-time transactions and, at the same time, to minimize the impact on the performance of non-real-time transactions. We have conducted a series of experiments based on a sanitized version of stock trading systems to evaluate the performance of both soft real-time and non-real-time transactions under different real-time supports in the system.

Secure Concurrency Control in Firm Real-Time Database Systems

Many real-time database applications arise in electronic financial services, safety-critical installations and military systems where enforcing security is crucial to the success of the enterprise. For real-time database systems supporting applications with firm deadlines, we investigate here the performance implications, in terms of killed transactions, of guaranteeing multilevel secrecy. In particular, we focus on the concurrency control (CC) aspects of this issue. Our main contributions are the following: First, we identify which among the previously proposed real-time CC protocols are capable of providing covert-channel-free security. Second, using a detailed simulation model, we profile the real-time performance of a representative set of these secure CC protocols for a variety of security-classified workloads and system configurations. Our experiments show that a prioritized optimistic CC protocol, OPT-WAIT, provides the best overall performance. Third, we propose and evaluate a novel “dual-CC” approach that allows the real-time database system to simultaneously use different CC mechanisms for guaranteeing security and for improving real-time performance. By appropriately choosing these different mechanisms, concurrency control protocols that provide even better performance than OPT-WAIT are designed. Finally, we propose and evaluate GUARD, an adaptive admission-control policy designed to provide fairness with respect to the distribution of killed transactions across security levels. Our experiments show that GUARD efficiently provides close to ideal fairness for real-time applications that can tolerate covert channel bandwidths of upto one bit per second.

Transaction Scheduling in Distributed Real-Time Systems

In this paper, we study the performance of using optimistic approach to concurrency control in distributed real-time database systems (RTDBS). The traditional optimistic approach suffers from the problem of unnecessary restarts. Transaction restarts can significantly increase the system workload and intensify resource and data contention. In distributed environments, the complexity of the system and the high communication overhead exacerbate the problem. Therefore, the number of unnecessary restarts is the determinant factor that affects the performance of optimistic approach in distributed RTDBS. When optimistic approach is extended to distributed environments, a number of issues resulting from the increased complexity and communication overhead have to be resolved. In this paper, a new real-time distributed optimistic concurrency control (DOCC) protocol with dynamic adjustment of serialization order (DASO), called DOCC-DA is proposed. This protocol can avoid unnecessary transaction restarts by dynamically adjusting the serialization order of the conflicting transactions. Therefore, resources can be saved and more transactions can meet their deadlines. In the DOCC-DA protocol, a new distributed circular validation scheme is included to facilitate transaction validation in distributed environments. The performance of the DOCC-DA protocol has been examined in detail by simulation. The results showed that the performance of the DOCC-DA protocol is consistently better than that of other protocols.

The Reduced Ceiling Protocol for Concurrency Control in Real-time Databases with Mixed Transactions

This paper proposes a real-time concurrency control protocol called Reduced Ceiling Protocol (RCP) for real-time database systems (RTDBS) consisting of hard and soft real-time transactions. The schedulability of hard real-time transactions can be improved by bounding the blocking time from soft real-time transactions. Different concurrency control strategies are proposed to resolve data conflicts between different combinations of hard and soft real-time transactions, and the properties of the RCP schedules are shown. In the RCP, methodologies are proposed to reduce the number of aborts for soft real-time transactions due to data conflicts with hard real-time transactions. Simulation experiments have been performed to study the performance of the RCP as compared with the optimistic concurrency control with wait 50 (OCC wait-50) under different workloads of soft real-time transactions, various ratios of read/write operations, and deadline constraints. It has been found that the RCP can not only guarantee the performance of hard real-time transactions but also reduce the number of deadlines missed of the soft real-time transactions under all situations.

A real-time concurrency control protocol for main-memory database systems

Protocols developed so far for concurrency control in real-time database systems have assumed a dynamic acquisition of data resources as it is impossible to predict which instances of relations will actually be accessed by each transaction. In this paper ‡ ‡ A summary of the ideas presented in this paper has appeared in SIGMOD Record, Special Issue on Real-Time Databases, 25(1):23–25 (1996). , we present a new concurrency control protocol for main-memory real-time database systems, which is based on predeclaration of data requirements at a relation granularity. When a transaction is submitted, it is possible to detect with simple syntactical means which relations will be accessed by the transaction. Preacquisition of data resources enables the system to execute transactions in a conflict-free manner. The protocol also offers the possibility of determining execution times without the effects of blocking and I/O, thereby allowing us to give guarantees for the execution of high-priority transactions. Through a series of simulation experiments, the protocol is compared against some typical concurrency control protocols proposed recently for real-time database systems.

Secure transaction processing in firm real-time database systems

Many real-time database applications arise in safety-critical installations and military systems where enforcing security is crucial to the success of the enterprise. A secure real-time database system has to simultaneously satisfy who requirements guarantee data security and minimize the number of missed transaction deadlines. We investigate here the performance implications, in terms of missed deadlines, of guaranteeing security in a real-time database system. In particular, we focus on the concurrency control aspects of this issue. Our main contributions are the following: First, we identify which among the previously proposed real-time concurrency control protocols are capable of providing protection against both direct and indirect (covert channels) means of unauthorized access to data. Second, using a detailed simulation model of a firm-deadline real-time database system, we profile the real-time performance of a representative set of these secure concurrency control protocols. Our experiments show that a prioritized optimistic concurrency control protocol. OPT-WAIT, provides the best overall performance. Third, we propose and evaluate a novel dual approach to secure transaction concurrency control that allows the real-time database system to simultaneously use different concurrency control mechanisms for guaranteeing security and for improving real-time performance. By appropriately choosing these different mechanisms, we have been able to design hybrid concurrency control algorithms that provide even better performance than OPT-WAIT.

Impact of high speed network on performance of real-time concurrency control protocol

Abstract The impact of network layer assumptions on the performance of the concurrency control protocol in distributed real-time database systems is studied by modeling the network layer as ATM networks instead of conventional simple constant delay centers. The results show that the unpredictable behaviour of the underlying network will give non-constant network transit time which in turn can cause significant adverse impact on the performance of the protocol. In this study, a dynamic deadline assignment scheme is proposed to reduce the impact of the underlying network and to improve the system performance.

Exploiting main memory DBMS features to improve real-time concurrency control protocols

Exploiting main memory DBMS features to improve real-time concurrency control protocols

Processing real-time transactions in a replicated database system

A database system supporting a real-time application has to provide real-time information to the executing transactions. Each real-time transaction is associated with a timing constraint, typically in the form of a deadline. It is difficult to satisfy all timing constraints due to the consistency requirements of the underlying database. In scheduling the transactions it is aimed to process as many transactions as possible within their deadlines. Replicated database systems possess desirable features for real-time applications, such as a high level of data availability, and potentially improved response time for queries. On the other hand, multiple copy updates lead to a considerable overhead due to the communication required among the data sites holding the copies. In this paper, we investigate the impact of storing multiple copies of data on satisfying the timing constraints of real-time transactions. A detailed performance model of a distributed database system is employed in evaluating the effects of various workload parameters and design alternatives on the system performance. The performance is expressed in terms of the fraction of satisfied transaction deadlines. A comparison of several real-time concurrency control protocols, which are based on different approaches in involving timing constraints of transactions in scheduling, is also provided in performance experiments.

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.

Prescheduling policy for real-time concurrency control: A performance evaluation

A new priority management policy, aprescheduling policy, is proposed. This policy can be applied on any conventional concurrency control protocol to schedule a real-time transaction. Costly preemption is avoided by the prescheduling policy, and parsing dataset of a transaction is not needed. Three widely used conventional concurrency control protocols (dynamic two-phase locking, basic timestamp ordering, and optimistic) are incorporated with the prescheduling policy to form three real-time concurrency control protocols. Performance of the three protocols is evaluated from three different viewpoints: database management systems, protocols, and transaction. From a database management system viewpoint, we show the prescheduling policy can improve the performance of protocols by raising thevalid ratio and reducingrestart counts. In general, two-phase locking with the prescheduling policy performs the best in most cases and yields the best choice for concurrency control in a real-time application. Deciding factors that affect performance of each protocol are identified from protocol viewpoint. Some suggestions are given for writing a timely transaction from the aspect of transaction viewpoint.

Concurrency control for distributed real-time databases

The concurrency control of transactions in a real-time database must satisfy not only the consistency constraints of the database but also the timing constraints of individual transactions. In this paper, we present a real-time concurrency control protocol that can be used in a distributed and decomposable real-time database. The protocol is based on the integration of a modular concurrency control theory with a real-time scheduling protocol called the priority ceiling protocol. This protocol supports the replication of data objects and avoids the formation of deadlocks. Finally, an analysis of the performance of this protocol is presented.