数据库集群的"无应答严次序发布传播"复制策略

数据库集群服务器的关键技术是数据复制，本文在对比分布式文件系统、可靠型多播、对象组服务以及分布式内存等技术的基础上，提出了“无应答严次序发布传播”复制策略，“发布传播”类似但不同于“发布订阅”模型。该策略采用了IP多播、双钥锁和基于全局／局部／状态次序编号的次序管理机制。双钥锁允许加锁者或下一个申请者释放互斥锁。次序管理遵循4个原则来避免“乱序”、“意图歪曲”、“因果牵制”和“反向因果牵制”四个数据不一致问题。本文详细讨论了该策略的设计目标、主要问题及解决途径、特征、基本原则以及算法轮廓。     

CSB21A型备自投装置使用中的问题及探讨

针对CSB21A型备用电源自动投入装置在现场应用中遇到的问题,进行了分析及探讨.回路改进后提高了系统的稳定性及供电可靠性.     

Distributed Multi-Level Recovery in Main-Memory Databases

In this paper we present recovery techniques for distributed main-memory databases, specifically for client-server and shared-disk architectures. We present a recovery scheme for client-server architectures which is based on shipping log records to the server, and two recovery schemes for shared-disk architectures—one based on page shipping, and the other based on broadcasting of the log of updates. The schemes offer different tradeoffs, based on factors such as update rates.Our techniques are extensions to a distributed-memory setting of a centralized recovery scheme for main-memory databases, which has been implemented in the Dalì main-memory database system. Our centralized as well as distributed-memory recovery schemes have several attractive features—they support an explicit multi-level recovery abstraction for high concurrency, reduce disk I/O by writing only redo log records to disk during normal processing, and use per-transaction redo and undo logs to reduce contention on the system log. Further, the techniques use a fuzzy checkpointing scheme that writes only dirty pages to disk, yet minimally interferes with normal processing—all but one of our recovery schemes do not require updaters to even acquire a latch before updating a page. Our log shipping/broadcasting schemes also support concurrent updates to the same page at different sites.     

Violet

Violet is an easy-to-use theorem prover based on locking resolution, with integrated equality extensions that use term rewriting and Knuth–Bendix completion. Violet participated in the CADE-13 ATP System Competition.     

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.     

一个可处处中断的LOCK和UNLOCK算法

一般的锁操作中Ｌｏｃｋ和Ｕｎｌｏｃｋ语句需作为原语整体实施，即主要要求加锁的锁状态检查和加锁动作不可中断，与一般的锁操作法不同，本文给出一个可以处处被其他进程任意中断的锁操作Ｌｏｃｋ和Ｕｎｌｏｃｋ的算法，并通过其在异构数据库系统中的一个应用，阐明了它在实现互斥操作和并发控制等方面的实用价值。     

采用高级语言对硬盘加密的方法

本文提出了一种基于DOS本身特点的硬盘加密方法，它具有不破坏DOS文件和磁盘结构、支持磁盘优化软件、加密点隐蔽、兼容性好等特点．     

基于数字锁相环的中波激励器在广播发射系统中的应用

激励器是广播发射系统中必不可少的部件之一。本文介绍一种基于数字锁相技术的中波激励器．阐述了其工作原理并给出了实现电路。     

Optimization of stress modes by energy compatibility for 4‐node hybrid quadrilaterals

Optimal hybrid stress quadrilaterals can be obtained by adopting appropriate stresses and displacements, and satisfying the energy compatibility condition is shown to be an ultimate key to obtaining optimal stress modes. By using compatible isoparametric bilinear (Q₄) displacements and 5‐parameter energy compatible stresses of the combined hybrid finite element CH(0‐1), a robust 4‐node plane stress element ECQ₄ is derived. Equivalence to another hybrid stress element LQ₆ with 9‐parameter complete linear stresses based on a modified Hellinger–Reissner principle is established. A convergence analysis is given and numerical experiments show that elements ECQ₄/LQ₆ have high performance, i.e. are accurate at coarse meshes, insensitive to mesh distortions and free from locking. Copyright © 2003 John Wiley & Sons, Ltd.     

Two simple and efficient displacement‐based quadrilateral elements for the analysis of composite laminated plates

Two simple 4‐node 20‐DOF and 4‐node 24‐DOF displacement‐based quadrilateral elements named RDKQ‐L20 and RDKQ‐L24 are developed in this paper based on the first‐order shear deformation theory (FSDT) for linear analysis of thin to moderately thick laminates. The deflection and rotation functions of the element sides are obtained from Timoshenko's laminated composite beam functions. Linear displacement interpolation functions of the standard 4‐node quadrilateral isoparametric plane element and displacement functions of a quadrilateral plane element with drilling degrees of freedom are taken as in‐plane displacements of the proposed elements RDKQ‐L20 and RDKQ‐L24, respectively. Due to the application of Timoshenko's laminated composite beam functions, convergence can be ensured theoretically for very thin laminates. The elements are simple in formulation, and shear‐locking free for extremely thin laminates even with full integration. A hybrid‐enhanced procedure is employed to improve the accuracy of stress analysis, especially for transverse shear stresses. Numerical tests show that the new elements are convergent, not sensitive to mesh distortion, accurate and efficient for analysis of thin to moderately thick laminates. Copyright © 2004 John Wiley & Sons, Ltd.