Real-time Concurrency Control Research Articles

A new secure 2PL real-time concurrency control algorithm (ES2PL)

A secure concurrency control algorithms must be devoid of covert channels originating from data conflicts between transactions, in addition to ensuring database integrity. Current secure concurrency control algorithms mistreat transactions with higher access classes. Because it better solves the priority inversion problem. A widely used concurrency control algorithm is the two-phase locking with high priority (2 PL-HP). The inclusion of cyclic restart, deadlock, unnecessary abort, pseudo-priority inversion, and starvation, on the other hand, may reduce its performance. In this paper, a new enhanced of secure two-phase locking protocol with multilevel secure distributed database systems is presented, the idea of enhanced secure Two-Phase locking protocol by adding the security level to assign the priority to the transaction. The enhanced add a secure manager to decide the level of the security and give the instruction to process the transaction in real lock with data x/virtual lock with version data x0 or decided to Abort the transaction based on the security level. The suggested study intends to reduce transaction miss rate by addressing the following issues: deadlock by splitting the execution stage into locking and processing phases, it reduces unnecessary cycle restart, transaction aborts by checking the security priority level (high, medium, low), and generating virtual lock and versions data. Finally, simulation performance confirms that improvement in transactions miss's percent and reduction in transactions' rollbacks compared to other secure concurrency control.

Secure concurrency control protocol with timeliness guarantees in real-time database systems

Real-time database systems (RTDBSs) are usually applied in the time-critical applications with security constraints. For these applications, RTDBSs must simultaneously satisfy two requirements in guaranteeing data security and minimizing the deadline miss ratio for admitted transactions. Multilevel secure database systems based on mandatory access control can prevent direct unlawful information flows between transactions. However, they cannot be free from illegal information transfers between transactions by means of the concurrency control mechanism, so the novel concurrency control algorithms supporting security and real-time requirements are needed for RTDBSs. In this paper, we present a novel secure real-time concurrency control algorithm (SRCC) for RTDBSs. The SRCC makes an effective tradeoff between security constraints and timing constraints by introducing secure control factor and real-time influence factor. Further, in order to obtain the better real-time performance, an enhanced SRCC called ESRCC is proposed by introducing the concept of similarity. The experimental results show that the ESRCC can ensure excellent real-time performance while guaranteeing data security.

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.

Real-Time Multiversion Concurrency Control Based on Validation Factor

Real-Time Multiversion Concurrency Control Based on Validation Factor

Real-time Optimistic Concurrency Control based on Transaction Finish Degree

Concurrency control is one of the main issues in the studies of real-time database systems. Optimistic concurrency control algorithms have the attractive properties of being non-blocking and deadlock-free. However, they have the problems of late conflict detection and transaction restarts. Although the number of transaction restarts is reduced by dynamic adjustment of serialization order in real-time database systems, they are still some unnecessary transaction restarts. In this study, we propose a new method called Transaction Finish Degree (TFD) and a new Multiversion Optimistic Concurrency Control algorithm based on TFD (MVOCC-TFD), which can reduce the number of unnecessary restarts. Theoretical analysis and experimental results demonstrate that the new algorithm can outperform the previous ones

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.

Two-version based concurrency control and recovery in real-time client/server databases

While there has been a significant amount of research in real-time concurrency control, little work has been done in logging and recovery for real-time databases. This paper proposes a two-version approach which considers both real-time concurrency control and recovery. We propose a network-server-based architecture and algorithms which can not only reduce the blocking time of higher-priority transactions and improve the response time of client-side read-only transactions, but also provide a diskless runtime logging mechanism and an efficient and predictable recovery procedure. The performance of the algorithms was verified by a series of simulation experiments by comparing the algorithms with the well-known Priority Ceiling Protocol (PCP), the Read/Write PCP, the New PCP, and the 2-version two-phase locking protocol, for which we have very encouraging results. The schedulability of higher-priority transactions and the response time of client-side read-only transactions were all greatly improved.

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.

Validation concurrency control protocol in parallel real-time database systems

In parallel real-time database systems, concurrency control protocols must satisfy time constraints as well as the integrity constraints. The authors present a validation concurrency control(VCC) protocol, which can enhance the performance of real-time concurrency control mechanism by reducing the number of transactions that might miss their deadlines, and compare the performance of validation concurrency control protocol with that of HP2PL (High priority two phase locking) protocol and OCC-TI-WAIT-50(Optimistic concurrency control-time interval-wait-50) protocol under shared-disk architecture by simulation. The simulation results reveal that the protocol the author presented can effectively reduce the number of transactions restarting which might miss their deadlines and performs better than HP2PL and OCC-TI-WAIT-50. It works well when arrival rate of transaction is lesser than threshold. However, due to resource contention the percentage of missing deadline increases sharply when arrival rate is greater than the threshold.

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.

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.

Semantics-Based Transaction Processing for Real-Time Databases: The Case of Automated Stock Trading

In the future, automated stock trading (AST) databases will need to support execution of transactions with time constraints similar to that discussed in real-time databases. Transactions in AST databases repeat from a predictable set of transaction classes where the logical read-sets and write-sets of these classes can be established a priori. We propose a novel transaction management mechanism that exploits this a priori knowledge of data requirements to minimize wasted resources and transaction restarts inherent in existing real-time transaction processing mechanisms based on dynamic acquisition of resources. Preanalysis provides a mechanism to incorporate transaction semantics, identify potentially detrimental conflicts, and induce favorable serialization orders before transactions execute. By blocking potentially conflicting transactions, we incorporate an implicit overload management technique. Scheduling decisions can be made efficient to complement serialization orders, thus reducing unnecessary transaction restarts. Our protocol is evaluated using simulation and is shown to outperform existing real-time concurrency control mechanisms under various workload and resource parameters.

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.

Real-Time Transaction Scheduling: A Framework for SynthesizingStatic and Dynamic Factors

Real-time databases are poised to be an important component of complex embedded real-time systems. In real-time databases (as opposed to real-time systems), transactions must satisfy the ACID properties in addition to satisfying the timing constraints specified for each transaction (or task). Although several approaches have been proposed to combine real-time scheduling and database concurrency control methods, to the best of our knowledge, none of them provide a framework for taking into account the dynamic cost associated with aborts, rollbacks, and restarts of transactions. In this paper, we propose a framework in which both static and dynamic costs of transactions can be taken into account. Specifically, we present: i) a method for pre-analyzing transactions based on the notion of branch-points for data accessed up to a branch point and predicting expected data access to be incurred for completing the transaction, ii) a formulation of cost that includes static and dynamic factors for prioritizing transactions, iii) a scheduling algorithm which uses the above two, and iv) simulation of the algorithm for several operating conditions and workload. Our dynamic priority assignment policy (termed the cost conscious approach or CCA) adapts well to fluctuations in the system load without causing excessive numbers of transaction restarts. Our simulations indicate that i) CCA performs better than the EDF-HP algorithm for both soft and firm deadlines, ii) CCA is more fair than EDF-HP, iii) CCA is better than EDF-CR for soft deadline, even though CCA requires and uses less information, and iv) CCA is especially good for disk-resident data.

A real-time concurrency control algorithm: Use of multiversion and precedence relationships

Abstract This paper proposes a multiversion concurrency control algorithm for real-time databases. Based on a priority cognitive algorithm commonly used in real-time processing, the algorithm resolves data conflicts among conflicting transactions in favor of the urgent transactions, i.e., those with higher priority. Our algorithm is expected to minimize the transactions missing those deadlines and increase the degree of transaction concurrency by using precedence relationships and multiple versions. In the algorithm, a precedence relationship, which implies a serialization order among conflicting transactions, is utilized to resolve data conflicts. By exploiting precedence relationships, our algorithm can avoid deadlocks, and dynamically determine the abortion of lower priority transactions depending on the likelihood of rollbacks and the amount of the work done by the low priority transaction.