传感器网络中数据融合过程的事务分析与建模

传感器网络是计算机科学技术的一个新的研究领域，它综合了传感器技术、嵌入式计算技术、分布式信息处理技术和通信技术，能够协作地实时监测、处理各种环境或监测对象的信息并传送给用户，具有十分广阔的应用前景。本文以面向事务的观点，基于事务工作流模型，结合数据的时间特性、事务流的依赖关系及数据与事务流间的相互关联，提出事务的控制区域的概念并给出一种基于应用事务的行为语义控制区域的事务模型，为传感器网络数据融合过程提供一个适当的正式模板；给出该模型的提交、回滚、可见定理及规则；通过性能测试，表明该模型提高了数据的相对外化率；模型主要解决了在分布的多用户环境下系统如何控制应用，保证应用语义逻辑的一致性。     

工业监控系统中的分布式实时数据库研究

分析了工业监控系统中的分布式实时数据库的的功能与特点、结构、数据对象和事务的种类。提出建立内存数据库保证系统实时性并讨论了PC机和嵌入系统上实现内存数据库管理的区别和难点。着重研究了根据数据相关度分配数据的分布机制的实现和基于价值函数的事务并发调度。为构建工业监控系统中的分布式实时数据库提供了一条思路。     

基于数据时态特性的实时事务并发控制

通过对数据时态特性及其对事务调度的影响进行分析,提出了基于数据时态特性的实时事务并发控制算法.该算法根据数据截止期及事务的执行时间估算,改进了事务的验证规则,对事务的提交顺序进行调整,提高了系统的实时性能.理论分析与实验结果表明:该算法降低了事务重启个数及超截止期百分率,性能要优于已有的实时并发控制算法.     

EMS系统Mosaic与Oracle间接口的设计与实现

利用Mosaic系统对企业能源管理系统实时数据进行采集和监控,并将能源量进行统计管理,把EMS内部或外部原本孤立的系统和数据流程化地整合在一起是企业解决信息孤岛的一种方法.介绍EMS系统Mosaic与Oracle通信关键技术,设计实时数据的接口方案和通信规约,利用API方式进行不同系统间相互通信,实现不同系统的集成,达到信息的共享.     

移动分布式实时数据库中并发控制框架

在移动分布式数据库系统中采用三层结构，提出了DMVOCC-DA-2PLV（Distributed Multiversion Optimistic Concurrency Control—Dynamic Adjustment of Serialization Order-Two-Phase Local Validation）协议处理移动分布式实时事务。移动实时事务处理分两阶段进行。第一阶段在移动主机（MHs）上处理，并进行局部部分有效性检查性确认，使用向后有效性确认机制，与在服务器提交事务进行有效性确认。及早地检测数据冲突，节省了处理和通信资源。第二阶段在服务器处理，通过局部部分有效性确认的事务，提交到服务器进行局部最终有效性确认。协议消除了移动只读事务和移动更新事务的冲突，使用多版本动态调整串行次序技术，避免了不必要的事务重启动。如果移动只读事务所有读数据项通过局部部分向后有效性确认，则可提交，大大降低了移动只读事务的响应时间。在全局有效性确认中对分布更新事务进行检查，以保证分布串行性。通过模拟仿真，对DMVOCC-DA-2PV协议进行了性能测试，并与DTO-2PC和DHP-2PL进行了比较。实验结果表明DMVOCC-DA-2PV并发控制协议要优于其它协议。     

面向电力系统实时通信的应用层数据网关模型的设计

本文针对电力系统采用不同应用层协议通信,阻碍信息交换与共享的现状,提出一种面向电力系统实时通信的应用层数据网关模型。该模型成功地实现了信息在不同应用层协议间的传递、将分布在不同调度系统的实时数据及非实时数据通过远程网络统一管理起来。     

大数据流式计算框架Heron环境下的流分类任务调度策略

新型大数据流式计算框架Apache Heron默认使用轮询调度算法进行任务调度，忽略了拓扑运行时状态以及任务实例间不同通信方式对系统性能的影响。针对这个问题，提出Heron环境下流分类任务调度策略（DSC-Heron），包括流分类算法、流簇分配算法和流分类调度算法。首先通过建立Heron作业模型明确任务实例间不同通信方式的通信开销差异；其次基于流分类模型，根据任务实例间实时数据流大小对数据流进行分类；最后将相互关联的高频数据流整体作为基本调度单元构建任务分配计划，在满足资源约束条件的同时尽可能多地将节点间通信转化为节点内通信以最小化系统通信开销。在包含9个节点的Heron集群环境下分别运行SentenceWordCount、WordCount和FileWordCount拓扑，结果表明DSC-Heron相对于Heron默认调度策略，在系统完成时延、节点间通信开销和系统吞吐量上分别平均优化了8.35%、7.07%和6.83%；在负载均衡性方面，工作节点的CPU占用率和内存占用率标准差分别平均下降了41.44%和41.23%。实验结果表明，DSC-Heron对测试拓扑的运行性能有一定的优化作用，其中对接近真实应用场景的FileWordCount拓扑优化效果最为显著。     

多线程在数据接口设计中的应用

主要介绍电厂实时数采系统与ＭＩＳ系统的数据接口设计,即实现实时数采系统和ＭＩＳ系统的集成;同时介绍了有关线程、串口通信、自定义消息处理等概念以地多线程技术应用到数据接口设计中。     

VC＋＋下对大量实时数据的采集处理

对工控软件来讲，大量实时数据的采集往往会影响用户界面消息的响应时间，导致系统性能的下降，如果采用多线程来处理数据的采集与用户界面的消息，则会很好地提高系统的性能。     

飞行实时数据通信的Visual C++实现

介绍了FK－2飞行实时监控系统中地面站与机载设备的通信问题，地面站实时接收并处理数据的方法，以及地面站计算机网络间数据的发送与接收问题，详细阐述了通信中的时隙分配，在VisualC 中线程的使用，以及自定义网络数据格式和深度缓冲法。     

一种高效的合作实时事务并行检验点算法

许多数据和活动上都有很强时间性的应用在地理上同时具有分布性,这种应用需求使得分布式实时数据库的研完成为数据库研究领域的热点。在实时事务执行时,事务故障或数据竞争会导致事务重启,为了减少因重启而损失的工作量,可以采用检验点技术以利于事务时间正确性的满足。在一些分布式实时数据库应用中,不同结点的事务通过消息交换形成合作关系,当某一事务记检验点时,为保证合作事务间的全局一致性,相关事务也要相应地记检验点。传统的协同检验点方法没有考虑应用的定时约束,不能很好地支持分布式实时事务处理。本文提出了一种高效的并行协同检验点方法,该算法既具有最小协同检验点特性又使全局检验点过程延时最小。实验表明该算法减少了全局检验点阻塞时间,有利于分布式实时事务截止期的满足。     

支持分布式合作实时事务处理的协同检验点方法

在实时事务执行时，事务故障或数据竞争会导致事务重启，为减少事务重启损失的工作量，可以采用检验点技术保证事务的时间正确性．在一类分布式实时数据库应用中，不同结点的事务通过消息交换形成合作关系，为保证合作事务间的全局一致性，当某一事务记检验点时，相关事务也要记检验点．传统协同检验点方法没有考虑应用的定时约束，不能很好地支持分布式合作实时事务处理．该文提出了一种基于图论的协同检验点方法，利用在每个计算结点上为每个合作事务集维护的局部有向图，使用一个基于图论的计算过程标识出应记检验点的事务，该方法既具有最小协同检验点特性，又使全局检验点的时延最小．实验表明该算法减少了全局检验点时延，有利于实时事务截止期的满足．     

On Using Real-Time Static Locking Protocols for Distributed Real-Time Databases

The use of Static Two Phase Locking Protocols (S2PL) for concurrency control in real-time database systems (RTDBS) has received little attention in the past. Actually, real-time S2PL (RT-S2PL) protocols do possess some desirable features making them suitable for RTDBS, especially for distributed real-time database systems (DRTDBS) in which remote locking is required and distributed deadlock is possible. In this paper, different RT-S2PL protocols are proposed. They differ in their methods of reducing the blocking time of higher priority transactions. Their performance is studied and compared with a real-time dynamic two phase locking protocol (RT-D2PL), called Hybrid Two Phase Locking (Hb2PL). The impact of different system and workload parameters, such as mean inter-arrival time of transactions, number of remote lock requests of a transaction, communication overhead for sending messages, and database size on their performance have been examined. The performance results indicate that the RT-S2PL protocols are suitable for DRTDBS in which the proportion of local locks of a transaction is small and the communication overhead for locking is high.     

分布式短事务系统中提交协议的研究

分布式短事务系统具有事务简短、请求频繁的特点。现有的分布式提交协议多面向复杂的长事务应用场景,难以满足短事务处理的需求。针对分布式短事务系统的特点,提出一种新型的分布式事务提交方法。该方法在事务参与者之间建立互用日志,并通过询问协议进行交互,获得事务进展情况,从而减少了强制写日志次数和通信次数,优化了故障处理过程。与其他分布式提交协议和系统比较,本协议可以有效地提高事务效率,并具有更高的日志可用性。     

一种新的混合实时事务并发控制算法

单一的实时事务并发控制策略因为对事务性能以及事务对数据的访问方式有着特殊限制而无法满足不同类型事务同时并存的混合实时数据库的要求.针对不同类型实时事务特征,提出了一种新的混合实时事务并发控制算法,对不同类型实时事务采用不同并发控制策略,具有极强的针对性和自适应性,算法同时通过分析数据的相关语义,利用数据相似性定义,合理放宽可串行化的正确性标准,在优先考虑硬实时事务的前提下,尽可能增加软实时事务成功提交的比例以提高系统整体性能.仿真实验结果证明MRTT_CC算法性能良好.     

Using adaptive scheduling for increased resiliency in passive asynchronous replication

Distributed systems commonly replicate data to enhance system dependability. In such systems, a logical update on a data item results in a physical update on a number of copies. The synchronization and communication required to keep the copies of replicated data consistent introduce a delay when operations are performed. In systems distributed over a bandwidth-constrained area, such operational delays generally prove unacceptable and passive asynchronous replication is often used to mitigate the delays. The research described in this paper looks to develop a new methodology for passive asynchronous replication that includes the introduction of an adaptive data replication scheduler to increase the data redundancy of the most valued data objects in overloaded situations. The approach we describe relies on the batch processing nature of passive asynchronous replication to make update decisions based on a defined policy. The methodology uses an adaptive scheduling algorithm providing near real-time selection of which objects to replicate during overloaded conditions based on a trained multilayer perceptron neural network. Historical replication logs are used for the initial training of the network and supervised training continues as replication logs are created providing periodic improvement through a feedback mechanism. This paper presents summary results of data replication scheduling simulations with an emphasis on the design selection of the adaptive distributed scheduler. This research was supported in part by a research fellowship from the Naval Surface Warfare Center, Dahlgren Division. The views, opinions, and findings contained herein are those of the authors and should not be construed as an official Department of Defense position, policy, or decision.     

移动实时提交协议的恢复处理与通信分析

三层实时提交协议(3LRTC)是为支持事务移动性、断接性、实时性及功能替代性等设计的一种移动实时提交协议,该协议能保证移动分布式实时事务放松原子性和结构正确性。该文在分析移动实时事务各参与者提交状态变化的基础上,讨论了3LRTC在发生场地故障和断接时的恢复处理方式,以保证故障发生后数据库能恢复到一个正确的状态。该文还对3LRTC的通信代价进行了分析与比较,结果表明,三层提交结构能减少移动实时事务的通信消息数。     

Multidimensional Timestamp Protocols for Concurrency Control

We propose multidimensional timestamp protocols for concurrency control in database systems where each transaction is assigned a timestamp vector containing multiple elements. The timestamp vectors for two transactions can be equal if timestamp elements are assigned the same values. The serializability order among the transactions is determined by a topological sort of the corresponding timestamp vectors. The timestamp in our protocols is assigned dynamically and is not just based on the starting/finishing time as in conservative and optimistic timestamp methods. The concurrency control can be enforced based on more precise dependency information derived dynamically from the operations of the transactions. Several classes of logs have been identified based on the degree of concurrency or the number of logs accepted by a concurrency controller. The class recognized by our protocols is within D-serializable (DSR), and is different from all previously known classes such as two phase locking (2PL), strictly serializable (SSR), timestamp ordering (TO), which have been defined in literature. The protocols have been analyzed to study the complexity of recognition of logs. We briefly discuss the implementation of the concurrency control algorithm for the new class, and give a timestamp vector processing mechanism. The extension of the protocols for nested transaction and distributed database models has also been included.     

Parallel Concurrency Control Activity for Transaction Management in Real-time Database Systems

In a real-time database system, an application supports a mix of transactions. These include the real-time transactions that require completion by a given deadline. Time-critical requirements also exist in many distributed multi-media system applications. Existing concurrency control procedures introduce excessive delays due to non-availability of data resources. In this study, we ignore the delays incurred by ordinary transactions, in order to achieve a non-interference mode of execution (near parallel) for the time-critical transactions. For this purpose, a data allocation model has been studied. It is a stochastic process model based on the use of two-phase locking. It highlights the available possibilities for reductions of delays for time-critical transactions within a distributed real-time database systems. Based on the new conceptual model, modified synchronization techniques for time-critical transactions have been proposed.     

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