Optimistic Concurrency Control Algorithm Research Articles

Priority Heuristic in MDRTDBS

Background: Mobile distributed real time database is an emerging field of research. Transaction execute in these system should commit before elapsing the deadline. Assigning priority to arrived and executing transaction is the main function of transaction scheduler. Perform correct order of execution enhance the system performance in time constraint environment. In recent years a number of heuristic policies in DRTDBS are developed to enhance the quality estimation of scheduler. However due to various wireless limitations a very little work is investigated in the MDRTDBS. In this paper we have develop two heuristic policies and perform simulation using pessimistic and optimistic concurrency control algorithm to enhance the system performance. Objective: Two heuristic policies based on write only locks and number of same data item existence has been introduced. These heuristic approaches enhance the performance of MDRTDBS scheduler. Methods: Develop two heuristic policies based on data contention which cope with CC policies like DHP-2PL and FBOCC. These policies count the number of write only locks and existence of number of same data item. Ultimately these policies enhance the system performance. Results:: Investigated the performance using simulator which is designed using C language. Based on these simulation results using pessimistic and optimistic CCs different graphs are plotted which shows the performance of system for these developed heuristic approaches. During simulation the low and high workload of transaction arrival is taken to fair investigate of these heuristic approaches. Conclusion: Simulation results show that the system performance is improved using these heuristic approaches. However, NWL_Modified heuristic approach outperform in MDRTDBS than earlier heuristic approaches.

Multi-Version-PulsatingSTM: A Multi-Version Optimistic Concurrency Control Scheme for Highly Parallel in-Memory Workload in a Multi Core Environment

Large in-memory data structures have a significant application in the fields of graphics, gaming, military and all the possible areas where Big Data can be employed. Their fame in the area of science and technology is attributable to fast in-memory access by the processor as compared to on-disk data structures. These enormous data structures can be accessed still fast and efficiently through parallel computing. For employing highly parallel computations, equally parallel algorithms are required. One of the most desirable attributes of such algorithms is their ability to control concurrency and avoid any deadlocks while being time and energy efficient. This paper presents a multi-version optimistic concurrency control algorithm based on timestamping. This algorithm is lock free and is tested on 64 simulated CPU cores on a multi core simulator. The algorithm is a Software Transactional Memory approach employing 16, 32, 40 and 50 threads in different tests running on the simulator. Half of the threads are doing reading and half are doing writing operation in each case while accessing an in-memory dynamic array. Being lock free and employing lazy timestamp calculations, this approach is better than other existing concurrency control approaches.

PVBSSS: parallel validation-based shared-state scheduler

Shared-state schedulers have been proposed for resolving the scalability limitation of monolithic schedulers in large-scale server clusters. Recent studies have explored how to apply optimistic concurrency control (OCC) strategies on scheduling on large-scale clusters. However, the naive OCC can only detect some simple conflicts, and is not efficient on placing long decision time jobs. In this paper, we present the parallel validation-based shared-state scheduler (i.e., PVBSSS). It is an extended shared-state scheduler that aims for mixed short and long jobs scheduling in large-scale shared clusters. In PVBSSS, parallel validation is implemented as the OCC algorithm to ensure strong serialisability for concurrent scheduling transactions. Furthermore, admission control and a scheduling strategy are implemented in PVBSSS to alleviate scheduling conflicts between schedulers. We experimentally evaluated our approach using the Omega scheduler's public simulator and a cluster comprising 30 work nodes. We conjecture that our experimental study not only demonstrates the feasibility and efficiency of PVBSSS, but also will help developers to make more informed decisions on both designing and managing scheduling on large-scale cloud platform.

Managing concurrent execution of transactions in mobile ad-hoc network database systems: an energy-efficient approach

A Mobile Ad-hoc Network (MANET) is a collection of mobile, wireless and battery-powered nodes without any fixed infrastructure. Therefore, it fits well in mission-critical applications such as disaster rescue and military operations. However, when a node runs out of energy, communication may fail and transactions may be aborted if they are time-critical and miss their deadlines. In order to provide timely and correct results for multiple concurrent transactions, energy-efficient database concurrency control (CC) techniques become critical for database systems built for MANET. Due to the characteristics of MANET databases, existing CC algorithms cannot work effectively. In this paper, an energy-efficient CC algorithm is developed for mission-critical MANET databases in a clustered network architecture where nodes are divided into clusters, each of which has a cluster head, responsible for the processing of all nodes in the cluster. The cluster structure is constructed using a novel weighted clustering algorithm, which uses node mobility, remaining energy and workload to group nodes into clusters and select cluster heads. In our CC algorithm, we elect cluster heads to work as coordinating servers to conserve energy and balance energy consumption among servers, and propose an optimistic CC algorithm to offer high concurrency and avoid wasting limited system resources. Besides correctness proof and theoretical analysis, comprehensive simulation experiments were conducted, and simulation results show the superiority of our CC algorithm over existing techniques in terms of transaction abort rate, total energy consumption by all servers, and degree of balancing energy consumption among servers.

Optimistic concurrency control by melding trees

This paper describes a new optimistic concurrency control algorithm for tree-structured data called meld. Each transaction executes on a snapshot of a multiversion database and logs a record with its intended updates. Meld processes log records in log order on a cached partial-copy of the last committed state to determine whether each transaction commits. If so, it merges the transaction's updates into that state. Meld is used in the Hyder transaction system and enables Hyder to scale out without partitioning. Since meld is on the critical path of transaction execution, it must be very fast. The paper describes the meld algorithm in detail and reports on an evaluation of an implementation. It can perform over 400K update transactions per second for transactions with two operations, and 130K for transactions with eight operations.

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

Maintaining security and timeliness in real-time database system

Real-time database systems can have security constraints in addition to timing constraints. Such real-time systems are typically contained in environments that exhibit hierarchical propagation of information, where mandatory access control for security is required. Conventional multilevel secure (MLS) database models that implement mandatory access control are inadequate for time-critical applications and conventional real-time database models do not address security constraints. The objective of this work is to incorporate security constraints in real-time database systems in such a way that not only is security achieved, but achieving security does not degrade real-time performance significantly in terms of deadlines missed. We present two concurrency control algorithms for secure real-time databases: the Secure two-phase locking high priority (2PLHP) algorithm is based on a two-phase locking protocol and the Secure optimistic concurrency control (OPT) algorithm uses the properties of an optimistic concurrency protocol. We implement the two algorithms and study their performance using a real-time database system simulation model. Our study covers both soft and firm real-time databases. Results show that both the algorithms perform fairly well in terms of security and timeliness compared to non-secure algorithms. We show that achieving increased security does not necessarily mean an increased sacrifice in real-time performance.

Is a bird in the hand worth more than two in the bush? Limitations of priority cognizance in conflict resolution for firm real-time database systems

After a "boom" period from the late 80s to the early 90s, there appears to have been a reduction in the amount of work published on Concurrency Control (CC) in real-time database systems (RTDBS) in general and firm RTDBS in particular. This may be because existing paradigms (e.g., Optimistic CC) have been pushed to their limits and it is difficult to extract additional meaningful performance. One of the last unresolved bastions of real-time CC is the successful incorporation of priority cognizance. Researchers have speculated that priority cognizant optimistic concurrency control (OCC) algorithms, if designed well, could outperform priority insensitive ones in real-time database systems. So far, however, there is a distinct lack of conclusive proof available on this topic and the priority cognizant OCC algorithms that have appeared so far in the literature cannot claim unilateral superiority over their priority insensitive relatives. We thus surmise that successful incorporation of priority cognizance may lead to an increase in the performance of OCC protocols in firm RTDBSs. Based on this premise, we analyze the issue of priority cognizance and identify a critical condition that must hold for priority cognizant conflict resolution to work. The condition is that, on the average, the conflict sets of validating transactions should have a "large" number of transactions: We call this a bird in hand more than two in the bush phenomenon. Subsequently, we design a smart priority cognizant OCC variant, which we call OCC-APR, and analyze its performance, as well as that of several other concurrency control algorithms across a wide range of resource contention and system loading parameters. Surprisingly, it turns out that it is very difficult for priority cognizance to work as the above mentioned condition does not, usually,hold. We explain why this occurs and conclude that priority cognizance does not appear to be a promising technique to increase real-time CC performance. The contribution of this paper, thus, is to have laid to rest the "priority cognizance" issue with regard to real-time CCMs.

Precise serialization for optimistic concurrency control

Despite the fact that transaction implementation in most commercial database management systems uses locking for concurrency control, optimistic concurrency control has recently gained attention for its efficiency in new types of data-intensive applications such as computer-aided design, computer-aided software engineering, and computer integrated manufacturing applications. This paper describes and analyzes a new concurrency control algorithm referred to as precise serialization, a variation of an optimistic concurrency control algorithm using forward validation that is known to outperform other optimistic algorithms proposed so far. We show that the forward validation-based algorithm incurs transaction restarts which are not absolutely necessary to ensure data consistency, and that the precise serialization algorithm solves this problem with a reasonably limited amount of effort by dynamically adjusting transaction execution history. We illustrate, through simulation, that by removing such unnecessary restarts, the precise serialization algorithm improves the performance of the forward validation-based algorithm under certain conditions.

A Collaborative Environment for Authoring Large Knowledge Bases

Collaborative knowledge base (KB) authoring environments are critical for the construction of high-performance KBs. Such environments must support rapid construction of KBs by a collaborative effort of teams of knowledge engineers through reuse of existing knowledge and software components. They should support the manipulation of knowledge by diverse problem-solving engines even if that knowledge is encoded in different languages and by different researchers. They should support large KBs and provide a scalable and interoperable development infrastructure. In this paper, we present an environment that satisfies many of these goals. We present an architecture for scalable frame representation systems (FRSs). The Generic Frame Protocol (GFP) provides infrastructure for reuse of software components. It is a procedural interface to frame representation systems that provides a common means of accessing and modifying frame KBs. The Generic KB Editor (GKB-EDITOR) provides graphical KB browsing, editing, and comprehension services for large KBs. Scalability of loading and saving time is provided by a storage system (PERK) which submerges a database management system in an FRS. Multi-user access is controlled through a collaboration subsystem that uses a novel optimistic concurrency control algorithm. All the results have been implemented and tested in the development of several real KBs.

Value-cognizant speculative concurrency control for real-time databases

Speculative Concurrency Control (SCC) is a new concurrency control approach, especially suited for real-time databases. SCC capitalizes on the availability of unused resources in the system to ensure that serializable executions are discovered and adopted as early as possible, thus increasing the likelihood of the timely commitment of transactions with strict timing constraints. Using SCC, several shadow transactions execute on behalf of a given uncommitted transaction so as to protect against the hazards of blockages and restarts, which are characteristics of Pessimistic and Optimistic Concurrency Control algorithms, respectively. We describe the basic Order-Based SCC (SCC-OB) algorithm and demonstrate its excessive (exponential) use of shadowing. Next, we present SCC-kS, a more practical class of SCC algorithms that operate under a limited resources assumption. SCC-kS does not allow more than k shadows to execute on behalf of any given uncommitted transaction in the system. SCC-kS allows the system to constrain the level of speculation that each transaction is allowed to perform. This provides a straightforward mechanism for trading resources for timeliness. SCC-kS is proved correct by showing that it only admits serializable histories. Next, SCC with Deferred Commit (SCC-DC) is proposed. SCC-DC is a value-cognizant protocol because it utilizes information about transactions, such as deadline and criticalness, to improve timeliness through the controlled deferment of transaction commitments. We conclude our paper with an evaluation of the performance of SCC algorithms. We present simulation results, which show that SCC-based algorithms provide significant performance gains over other widely used concurrency control protocols for real-time databases.

Integrating standard transactions in firm real-time database systems

Real-time database systems are designed to handle workloads where transactions have completion deadlines and the goal is to meet these deadlines. However, many real-time database environments are characterized by workloads that are a mix of real-time and standard (non-real-time) transactions. Unfortunately, the system policies used to meet the performance goals of real-time transactions often work poorly for standard transactions. In particular, optimistic concurrency control algorithms are recommended for real-time transactions, whereas locking-based protocols are suited for standard transactions. In this paper, we present a new database system architecture in which real-time transactions use optimistic concurrency control and, simultaneously, standard transactions use locking. We prove that our architecture maintains data integrity and show, through a simulation study, that it provides significantly improved performance for the standard transactions without diminishing the real-time transaction performance. We also show, more generally, that the proposed architecture correctly supports the co-existence of any group of concurrency control algorithms that adhere to a standard interface.

A performance study of concurrency control in a real-time main memory database system

Earlier performance studies of concurrency control algorithms show that in a disk-resident real-time database system, optimistic algorithms perform better than two phase locking with higher priority (2PL-HP). In a main memory real-time database system, disk I/Os are eliminated and thus more transactions are enabled to meet their real-time constraints. Lack of disk I/Os in this environment requires concurrency control be re-examined. This paper conducts a simulation study to compare 2PL-HP with a real time optimistic concurrency control algorithm (OPT-WAIT-50) for a real time main memory database system, MARS. The results show that OPT-WAIT-50 outperforms 2PL-HP with finite resources.

Data access scheduling in firm real-time database systems

A major challenge addressed by conventional database systems has been to efficiently implement the transaction model, which provides the properties of atomicity, serializability, and permanence. Real-time applications have added a complex new dimension to this challenge by placing deadlines on the response time of the database system. In this paper, we examine the problem of real-time data access scheduling, that is, the problem of scheduling the data accesses of real-time transactions in order to meet their deadlines. In particular, we focus on firm deadline real-time database applications, where transactions that miss their deadlines are discarded and the objective of the real-time database system is to minimize the number of missed deadlines. Within this framework, we use a detailed simulation model to compare the performance of several real-time locking protocols and optimistic concurrency control algorithms under a variety of real-time transaction workloads. The results of our study show that in moving from the conventional database system domain to the real-time domain, there are new performance-related forces that come into effect. Our experiments demonstrate that these factors can cause performance recommendations that were valid in a conventional database setting to be significantly altered in the corresponding real-time setting.

New Paradigms for Real-Time Database Systems

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.

Improving the Performance of an Optimistic Concurrency Control Algorithm Through Timestamps and Versions

This correspondence describes and analyzes two schemes for improving the performance of serial validation, an optimistic concurrency control algorithm proposed by Kutng and Robinson. It is shown that timestamp-based techniques can be used to implement serial validation, yielding an equivalent algorithm with a much lower validation cost. A multiple version variant of serial validation is then presented, and simulation results indicate that multiversion serial validation has significant performance advantages over the single version algorithm.

Performance analysis of locking and optimistic concurrency control algorithms

New analytic models are presented which predict the maximum throughput of locking and optimistic concurrency control algorithms for a centralized database system. By making several simplifying assumptions, these models can be easily solved. The analytic results are tested against simulation and are shown to have an accuracy considerably better than some previously reported methods. The models are used to carry out a comparison between locking and optimistic control under stated assumptions. It is found that locking schemes consistently have higher maximum throughput than optimistic schemes.