基于多代理和多优先队列的短信实时并发算法

针对Modem发送短信在实时性、并发性及完整性等性能上存在的缺陷,提出基于多代理、多优先级队列的短信实时并发算法。该算法采用多代理、多优先级队列、线程池等技术手段保证短信控制的实时性、并发性及数据完整性,在算法中使用优先级,使某些信息能够优先发送。通过改造排队论模型和实验对算法进行验证,并将该算法应用于SMAS系统,系统运行结果表明,该算法大幅提高了其发送和接收短信的速度与效率,实现了短信实时性和并发性的目标,优化了SMAS系统的整体性能。     

虚拟多端口的短信分发调度系统模型

针对短信虚拟运营商短信多端口下发问题,提出一种基于模型的动态负载均衡下发调度系统模型。首先根据所设计的系统总体架构引出了系统的应用模型,接着通过排队论知识进行模型的分析与论证,并且引入动态负载均衡和多线程调度策略。通过理论和实践证明,该系统模型是可以确保短信应用的高并发性、实时性和负载均衡的。     

充电设施监控系统中的数据并发控制研究

针对充电设施监控系统在大并发数据处理上的难点,提出基于M/M/c排队论模型的数据并发控制算法。对数据帧在监控系统中的传输过程进行分析,确定解决通信服务器中数据传输的实时性和并发性问题是提高监控系统性能的关键。根据随机过程理论得到充电机数据帧进入通信服务器的过程服从泊松分布的结论,利用排队论建立并发控制算法的数学模型,采用多线程和多队列技术实现数据并发处理算法。根据性能指标,对损失代价和最优网关数量的关系进行定量分析,得到求解最优网关数量的优化方法。将并发处理算法应用到大型充电站中进行分析实验,结果表明,该算法不仅能够满足数据帧传输的实时性和并发性需求,且证明了网关优化方法可准确推导出最优网关的数量。     

MDB负载均衡和异步并发的短信分发系统研究

针对单线程短信系统和单一同步机制的多线程短信系统在处理分发短信的大数据量和高并发量的不足,为了确保大量的短信息应用的实时性,提出基于MDB动态负载均衡算法和异步并发多线程调度策略的短信分发系统,详细描述该系统的整体设计方案和使用的算法策略,并且实现该系统和进行实验测试。通过实验证明,该系统是可以确保短信应用的高并发性和实时性。     

改进线程池的移动通信数据传输系统优化

短信数据的提交、存储、处理、转发是移动通信传输系统的关键步骤。引入线程池概念和队列存储机制,应用到移动通信数据传输系统,并设置阀值点限定短信网关流量,建立基于多线程、分层处理的移动通信数据传输系统架构;在多线程模块提出基于排队原理的请求等待模型,并引入阻塞线程过程,设计线程动态调度算法。以某移动运营商的客户营销服务数据为背景,利用提出的系统架构方法建立短信发送平台,通过实验对比验证了该方法有效地改善了系统性能。     

基于事件驱动的Unix并发控制算法

以实际项目为开发背景,提出了基于事件驱动的并发控制算法,采用多线程、多队列和线程池等技术来保证系统的实时性、并发性和数据共享性。通过仿真对该算法进行了验证,结果表明,该算法能够实现系统的功能,提高系统的运行效率。     

固定优先级抢占调度算法下非周期任务实时性能研究

嵌入式实时系统不仅要在功能上满足需求,而且要在性能上满足实时性需求.给定调度算法,实时性取决于各个任务的到达特征和执行时间.任务的到达特征由应用环境决定.为此,本文研究任务执行时间对实时性能的影响,为嵌入式系统设计提供参考.针对固定优先级抢占调度算法,应用排队论,提出一种非周期实时任务的理论模型.该理论模型包含两个优先级不同的非周期实时任务,给出了任务的执行时间长短对时限错过率、任务响应时间、任务队列长度等实时性能的影响.给出一个应用实例,仿真结果验证了理论模型的正确性.     

面向实时流处理的多核多线程处理器访存队列

针对多核多线程处理器中乱序访存影响计算实时性的问题,在对典型访存队列进行研究的基础上提出了一种新的访存队列构建模型及其硬件结构.该模型采用窗口优化算法控制最差情况下的访存延迟,保证访存的实时性,同时又利用优化的乱序调度策略减少访存延迟.实验证明,该访存队列可控制最大访存延迟,与顺序访存相比,存储器具备更高的带宽,与传统的乱序访存相比较,可以充分满足计算的实时性需求,而存储器有效带宽基本不受影响,解决了多核多线程处理器承担实时流计算的基础难题.     

实时集群系统设计与性能分析

设计和构建了一个高可用性冗余实时集群系统,讨论了系统并行计算的实现和冗余机组调度策略,建立了系统的M/M/N排队论模型,并依据此模型对系统进行了性能分析。经测试证明,系统具有较高的可用性和实时性,可作为周期性高强度多源浮点信息处理平台,用于军事指挥控制等实时性要求较高的领域。     

虚拟多端口的短信分发系统设计与实现

针对虚拟短信端口的下发问题,文中设计并实现了一种基于多端口的动态负载均衡和多线程策略相结合的短信分发系统。首先提出了基于中国电信ISAG的MSDS系统总体架构,针对大数据量短信分发,接着引入动态负载均衡和基于MDB异步并发多线程相结合的分发策略,最后给出了基于EJB和Web Service的系统实现以及详细的测试结果。通过实践结果表明,该系统是可以确保短信分发应用的高并发性、实时性和负载均衡的,并且可以很好地解决不同平台应用的问题。     

一种基于乐观方法的安全实时并发控制协议

实时数据库通常应用在一些安全关键类应用中，如电子商务、股票交易、军事指挥系统等。在这样一些应用中，实时数据库系统需同时满足两方面的需求：确保数据安全和尽可能减低实时事务错过截止期的比率。然而，通常这两方面需求是相互冲突的，满足一方面是以牺牲另一方面为代价。本文提出了一种基于乐观方法的安全实时并发控制协议，该协议将安全约束整合到实时乐观并发控制协议中，并能根据应用的需求在安全性和实时性方面进行了适当的折中。性能测试结果显示，该协议在确保数据安全的同时并未明显地降低实时性能。     

发布/订阅通信模式的实时性能分析与评估

运用成熟的队列理论知识,通过PRISM模型验证工具,对发布/订阅模式的实时性能进行形式化分析。实验结果表明,发布/订阅模式在消息响应时间及消息传输可靠性两方面比传统的通信模式表现出更良好的性能,该实验模型和实验方法对于优化发布/订阅模式及调整实际发布/订阅系统中的参数配置都有一定的帮助。     

一种面向混合实时事务调度的并发控制协议

首先给出了一个两层结构的混合实时数据库系统模型,其中支持采用非定期任务调度算法来改进系统的性能．进一步,针对这种模型下混合事务的数据一致性问题,提出了一种新的并发控制协议——MCC-DATI．该协议采用动态优先级驱动的调度算法,通过限制非定期的软实时事务对硬实时事务的阻塞时间,保证硬实时事务的可调度性;同时,采用非定期任务调度算法以及基于时间戳间隔的动态串行化顺序调整机制来减少软实时事务的截止期错失率．仿真实验表明,相对于先前的混合事务的并发控制协议,该协议在不同的系统负载与截止期约束下都能够改进系统的性能。     

MIRROR: a state-conscious concurrency control protocol for replicated real-time databases

Data replication can help database systems meet the stringent temporal constraints of current real-time applications, especially Web-based directory and electronic commerce services. A prerequisite for realizing the benefits of replication, however, is the development of high-performance concurrency control mechanisms. In this paper, we present managing isolation in replicated real-time object repositories (MIRROR), a concurrency control protocol specifically designed for firm-deadline applications operating on replicated real-time databases. MIRROR augments the classical O2PL concurrency control protocol with a novel state-based real-time conflict resolution mechanism. In this scheme, the choice of conflict resolution method is a dynamic function of the states of the distributed transactions involved in the conflict. A feature of the design is that acquiring the state knowledge does not require inter-site communication or synchronization, nor does it require modifications to the two-phase commit protocol.Using a detailed simulation model, we compare MIRROR's performance against the real-time versions of a representative set of classical replica concurrency control protocols for a range of transaction workloads and system configurations. Our performance studies show that (a) the relative performance characteristics of these protocols in the real-time environment can be significantly different from their performance in a traditional (non-real-time) database system, (b) MIRROR provides the best performance in both fully and partially replicated environments for real-time applications with low to moderate update frequencies, and (c) MIRROR's simple to implement conflict resolution mechanism works almost as well as more sophisticated strategies.     

基于Hadoop的三队列作业调度算法

Hadoop集群单队列作业调度会产生短作业等待、资源利用率低的问题;采用多队列调度可兼顾公平、提高执行效率,但会带来手工配置参数、资源互占、算法复杂等问题。针对上述问题,提出三队列作业调度算法,利用区分作业类型、动态调整作业优先级、配置共享资源池、作业抢占等设计,达到平衡作业需求、简化一般作业调度流程、提升并行执行能力的目的。对短作业占比高,各作业占比均衡以及一般作业为主,偶尔出现长、短作业三种情况与先进先出(FIFO)算法进行了对比实验,结果三队列算法的运行时间均比FIFO算法要少。实验结果表明,在短作业聚集时,三队列算法的执行效率提升并不显著;但当各种作业并存且分布均衡时,效果很明显,这符合了算法设计时短作业优先、一般作业简化流程、兼顾长作业的初衷,提高了作业整体执行效率。     

Multiversion locking protocol with freezing for secure real-time database systems

Database systems for real-time applications must satisfy timing constraints associated with transactions. Typically, a timing constraint is expressed in the form of a deadline and is represented as a priority to be used by schedulers. Recently, security has become another important issue in many real-time applications. In many systems, sensitive information is shared by multiple users with different levels of security clearance. As more advanced database systems are being used in applications that need to support timeliness while managing sensitive information, there is an urgent need to develop protocols for concurrency control in transaction management that satisfy both timing and security requirements. In this paper, we propose a new multiversion concurrency control protocol that ensures that both security and real-time requirements are met. The proposed protocol is primarily based on locking. However, in order to satisfy timing constraints and security requirements, a new method, called the freezing method, is proposed. In order to show that our protocol provides a higher degree of concurrency than existing multiversion protocols, we define a new serializability for multiversion concurrency control, called FR-serializability, which is more general than traditional serializability. We present several examples to illustrate the behavior of our protocol, along with performance comparisons with other protocols. The simulation results show significant performance improvement of the new protocol.     

Algorithm to Process Read-only Transactions in Real-time Environments

In this study, we investigate a different approach to maintaining serializability in real-time database systems (RTDBS) such that concurrency among transactions can be increased. The study is motivated by the dominance of read only transactions (ROTs) in many real-time applications. Given the knowledge about the read/write characteristics of transactions, it can be more efficient and effective to process ROTs separately from update transactions (UTs). In particular, we have devised an independent algorithm to process ROTs while a conventional concurrency control protocol such as optimistic concurrency control (OCC) can be employed to process UTs. Using a separate algorithm to process ROTs can reduce the interference between UTs and ROTs. The undesirable overhead caused by transaction restart and blocking due to concurrency control can be alleviated. Consequently, the timeliness of the system can be improved. The performance of using this approach is examined through a series of simulation experiments. The results showed that the performance of ROTs in terms of miss rate and restart rate is improved significantly while the performance of UTs is also improved slightly. As a result, separate processing of ROTs is a viable approach that achieves better performance and resource utilization than using solely the OCC protocol, one of the best performing protocols in the literature of real-time database.     

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.