一种基于时间翟的面向对象数据库的并发控制算法

本文提出了一种基于时间戳的面向对象数据库的并发控制算法。设计这一算法时，我们首先按照ＯＯＤＢ的数据模型对传统的时间翟算法进行了扩展，然后利用抽象数据类型的语义定义了相容性矩阵，对不同级别的并行性冲突操作进行 不的处理，从而达到在系统开销尽可能小的情况下，心可大地增数据库存取操作的并发度的效果。     

数据库应用系统的数据并发访问问题探讨

本文描述了数据库应用系统并发访问的两个问题，讨论了ＯＲＡＣＬＥ和ＦｏｘＰｒｏ数据库系统的封锁机制，并给出利用封锁机制解决这两个问题的方法。     

面向对象数据库中对象的表达和操作

面向对象数据库管理系统是目前数据库发展和研究的热点。本文结合华中理工大学ＣＡＤ中心开发的面向对象数据库管理系统ＧＨＥＯＤＢ对对象的表达和处理作了一定的研究。对面向对象数据模型进行了对象的分类处理并为各种类型的对象设计了在系统内部的表达方式，另外本文还研究了对象的操作策略和在ＧＨＥＯＤＢ内部对对象进行常规处理的方法。     

ODBC技术在工程CAD系统中的应用

该文为了解决工程ＣＡＤ系统中数据处理效率低的问题，提出了采用ＯｐｅｎＤａｔａｂａｓｅＣｏｎｎｅｃｔｉｖｉｔｙ（开放式数据库联接，ＯＤＢＣ）的技术把不同类型的输入、输出数据定向于数据库管理系统中，同时利用了ＭＦＣ（ＭｉｃｒｏｓｏｆｔＣ基本类库）中的ＤＡＯ（数据库存取对象）技术对数据库进行管理和查询，从而提高了整个ＣＡＤ系统的集成化程度。并以一个基于ＯＤＢＣ的轻钢厂房ＣＡＤ系统为例子进行深入的阐述。     

XDOODB：一种支持关系模型和数据库方法的OODBMS

本文所述的研究工作，是在ＯＯＤＢＭＳ中同时支持面向对象数据模型和关系数据模型，实现包括对象操作（即数据库方法）在内的同一体化对象管理，并研制了一个相应的原型系统ＸＤＯＯＤＢ。在ＸＤＯＯＤＢ中，我们设计和实现了一种基于ＳＱＬ的数据库语言ＯＳＱＬ，提出了虚拟方法的概念，实现了一种Ｃ＋＋预编译器，使之可自动产生虚拟方法体，所提供的方法服务器以对用户透明的方式可进行数据库方法的存储、动态加载和运行，并采用     

基于数据分区的DBSCAN算法

数据聚类在数据挖掘、模式识别、图像处理和数据压缩等领域有着广泛的应用。ＤＢＳＣＡＮ是一种基于密度的空间聚类算法,在处理空间数据时具有快速、有效处理噪声点和发现任意形状的聚类等优点,但由于直接对数据库进行操作,在数据量大的时间就需要较多的内存和Ｉ／Ｏ开销;此外,当数据密度和聚类间的距离不均匀时聚类质量较差,为此,在分析ＤＢＳＣＡＮ算法不足的基础上,提出了一个基于数据分区的ＤＢＳＣＡＮ算法,测试结果表     

ADA—DDBMS中的并发控制

并发控制是ＤＤＢＭＳ（分布式数据库管理系统）中事务管理的重要功能．本文介绍了一种基于封锁的积极方法与消极方法相结合的并发控制策略．它根据全系统实际运行的即时状态，动态地决定对事务采取的执行策略，大大减少了积极封锁所易产生的死锁情况，同时又改善了消极封锁效率低的问题．     

演绎的面向对象数据库

本文回顾了演绎数据库（ＤｅＤＢ）和面向对象数据库（ＯＯＤＢ）的发展历史，综述了已取得的主要成果，讨论了研究的主要特征、存在的问题以及未来的发展方向。在此基础上，本文着重论述了演绎的面向对象数据库（ＤＯＯＤ）作为集成ＤｅＤＢ和ＯＯＤＢ理论和技术的新领域所涉及到的值得进一步的问题、目前采用的方法和取得的成果。此外，本文还讨论了ＤＯＯＤ系统开发的技术可能性，分析了实现ＤＯＯＤ系统的各种途径的可行性和技术关键。     

如何清除ORACLE服务器中非正常的会话

１．引言大型数据库是一个共享资源,多个用户程序可并行地存取数据库,如果不对并发操作进行控制,会存取不正确的数据或破坏数据库数据的一致性。ＯＲＡＣＬＥ利用事务和封锁机制提供数据并发存取和数据完整性,在一事务内由语句获取的全部封锁在事务期间被保持,直至该事务提交或回滚时被释放。对于用ＯＲＡＣＬＥ７数据库服务器构造的较大规模的企业级客户／服务器应用系统,众多的客户端由于各种各样的原因（硬件故障、意外掉电等等）难免造成用户会话的意外中止,而ＯＲＡＣＬＥ本身不主动清除这些垃圾会话（ｓｅｓｓｉｏｎ）,如果这…     

多级安全面向对象数据库的并发控制模型

本文论述多级安全面向对象数据库系统的事务管理。首先介绍两种新的用于面向对象数据库的安全性质，随后指出传统的冲突串行化并发控制算法中存在的隐藏通道，提出将ＲＯＬＬ算法和ＯＯＤＢ的版本控制相结合的方法。     

Towards a General Concurrency Control Algorithm for Database Systems

The concurrency control problem in database systems has been examined by many people and several concurrency control algorithms have been proposed. The most popular algorithms are two-phase locking and timestamp ordering. This paper shows that two-phase locking and timestamp ordering are special cases of a more general concurrency control algorithm. This general algorithm is described in detail and is proven to work correctly. We show that two-phase locking and timestamp ordering represent the two end points of a series of concurrency control algorithms. Each of them is a special case of the general algorithm proposed in this paper. Moreover, each of these special cases can be selected in advance, and can even be changed dynamically during execution.     

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.     

Semantic multigranularity locking and its performance in object-oriented database systems

Concurrency control schemes for object-oriented database systems (OODBSs) used in the area of performance-critical applications should increase the degree of concurrency and decrease locking overhead in order to offer maximum performance. However, most commercially available OODBSs use conventional concurrency control schemes that never exploit the rich semantics of object-oriented data model, thus fail to offer better performance. In this paper, we propose a concurrency control scheme for OODBSs, called in-place semantic multigranularity locking (ISMGL), that not only exploits semantics regarding methods to enhance the concurrency degree, but also utilizes multigranularity locking rules to decrease locking overhead. The novel aspect of ISMGL is that it combines conventional multigranularity locking and nested transaction model with utilizing commutativity of methods. Our concurrency control scheme is applicable for realistic OODBSs in the presence of complex objects with shared subobjects. Lastly, we evaluate the performance of ISMGL by using a simulation study.     

一种改进的动态调整串行化顺序算法

乐观并发控制协议比锁机制更适用于实时数据库,但其中存在着不必要的重启及重大重启。该文针对OCC-TI算法的不足,将动态调整串行化顺序方法从优先权和最终时间戳选择机制2方面进行了扩展,提出了新的基于时间戳的并发控制算法——OCC-CPTI。仿真实验证明,OCC-CPTI算法在性能上优于OCC-TI。     

The partitioned synchronization rule for planar extendible partialorders

The partitioned synchronization rule is a technique for proving the correctness of concurrency control algorithms. Prior work has shown the applicability of the partitioned synchronization rule to hierarchically decomposed databases whose structure is restricted to semitrees. The principal contribution of the paper is a demonstration that the partitioned synchronization rule also applies to more general structures than semitrees, specifically, to any planar extendible partial order, a partial order which when extended with a least and a greatest element still remains planar. To demonstrate utility, the paper presents two applications of the partitioned synchronization rule. The first application shows correctness of a component based timestamp generation algorithm suitable for implementing a timestamp ordering concurrency control algorithm. The second application shows correctness of a snapshot algorithm for concurrency control in a replicated multilevel secure database; we choose this application to highlight that hierarchically decomposed databases and multilevel secure databases are structurally similar. In both cases, the correctness proofs via the partitioned synchronization rule are substantially simpler than corresponding direct proofs     

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。     

Divergence control algorithms for epsilon serializability

The paper presents divergence control methods for epsilon serializability (ESR) in centralized databases. ESR alleviates the strictness of serializability (SR) in transaction processing by allowing for limited inconsistency. The bounded inconsistency is automatically maintained by divergence control (DC) methods in a way similar to SR is maintained by concurrency control (CC) mechanisms. However, DC for ESR allows more concurrency than CC for SR. The authors first demonstrate the feasibility of ESR by showing the design of three representative DC methods: two-phase locking, timestamp ordering and optimistic approaches. DC methods are designed by systematically enhancing CC algorithms in two stages: extension and relaxation. In the extension stage, a CC algorithm is analyzed to locate the places where it identifies non-SR conflicts of database operations. In the relaxation stage, the non-SR conflicts are relaxed to allow for controlled inconsistency. They then demonstrate the applicability Of ESR by presenting the design of DC methods using other most known inconsistency specifications, such as absolute value, age and total number of nonserializably read data items. In addition, they present a performance study using an optimistic divergence control algorithm as an example to show that a substantial improvement in concurrency can be achieved in ESR by allowing for a small amount of inconsistency     

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.     

数据库系统的优化并行控制算法

The concurrency control problem in database systems has been examined by many people and several concurrency control algorithms have been proposed. The most popular algorithms are two-phase locking and timestamp ordering. Due to its inefficiency in some situations, we propose the optimized method which is combined of timestamp ordering and optimistic method. With this method, the efficiency can be improved in those systems where the conflicts between transactions rarely happen.     

A multi-granularity locking model for concurrency control inobject-oriented database systems

A locking model adopting a multi-granularity approach is proposed for concurrency control in object-oriented database systems. The model is motivated by a desire to provide high concurrency and low locking overhead in accessing objects. Locking in schemas and locking in instances are developed separately and then are integrated. Schema changes and composite objects are also taken into account. A dual queue scheme for efficient scheduling of lock requests is developed. The model consists of a rich set of lock modes, a compatibility matrix, and a locking protocol. Characteristic query examples on single class, class lattice, and composite objects are used to illustrate the comparison between the ORION model and the proposed model. It is shown that our locking model has indeed made some improvements and is suitable for concurrency control in object-oriented databases