Structural locking mechanisms and their effect on database management system performance

Database management systems must provide a concurrency control subsystem to protect database consistency in the presence of concurrent readers and writers. The widely accepted method for realizing such protection in centralized database management systems is through a locking mechanism. The design of a locking mechanism for a relational database management systems presents the developer with a considerable number of new alternatives. This paper discusses some of those alternatives and their tradeoffs. A particular model is then presented which supports these alternatives for relational database management system locking mechanisms. A simulation model is described which was used to provide experimental results investigating these design alternatives. Results from a number of simulation experiments are presented demonstrating the effects on performance realized under different locking mechanism designs and transaction behavior profiles.     

Speculative locking protocols to improve performance for distributed database systems

We have proposed speculative locking (SL) protocols to improve the performance of distributed database systems (DDBSs) by trading extra processing resources. In SL, a transaction releases the lock on the data object whenever it produces corresponding after-image during its execution. By accessing both before and after-images, the waiting transaction carries out speculative executions and retains one execution based on the termination (commit or abort) mode of the preceding transactions. By carrying out multiple executions for a transaction, SL increases parallelism without violating serializability criteria. Under the naive version of SL, the number of speculative executions of the transaction explodes with data contention. By exploiting the fact that a submitted transaction is more likely to commit than abort, we propose the SL variants that process transactions efficiently by significantly reducing the number of speculative executions. The simulation results indicate that even with manageable extra resources, these variants significantly improve the performance over two-phase locking in the DDBS environments where transactions spend longer time for processing and transaction-aborts occur frequently.     

Principles of database management in a distributed system

The principles of database design in a distributed system are examined. The organization of the data, derived from a close analysis of data requirements and data usage, is the most important design decision. The type of system depends on the type of database and so does the manner in which decentralization is achieved.While only loose data integration is currently feasible in a distributed system, central control and standar dization is a valuable investment for the future.     

高校分布式数据库管理实验系统的设计与实现

目前,高校分布式数据库实验一般使用Oracle数据库管理系统.然而Oracle要经过复杂的数据管理和配置才能实现分布式数据库管理系统的技术和方法,也不利于学生对一些基本概念的理解.针对这一问题,设计并实现了基于C/S的同构型的高校分布式数据库管理实验系统,提出了系统的体系结构,定义了系统语法,并详细阐述了数据库字典、语法分析模块、定位模块等关键技术的设计.该系统能够满足高校分布式数据库实验的要求,对高校教学有一定的意义.     

基于DHP-2PL的分布式实时数据库的并发控制模型

介绍了几种用于RTDBS(实时数据库系统)中的并发控制模型以及它们在分布式环境下(DRTDBS)的拓展。根据DHP-2PL提出一种改进的并发控制模型。在该模型中,引入优先级分配机制和加锁检测机制。通过这两种机制可更好地协调DRTDBS中一致性与截止期的关系,同时也解决了DHP-2PL中事务高重启率的问题。     

Transaction Management in Distributed Database System POREL

This paper describes the architecture and implementation algorithm of a transaction managementsuhsystem (TM) in the distributed database system POREL.The TM has been reimplemented on VAX11/750.     

The Raid distributed database system

Raid, a robust and adaptable distributed database system for transaction processing, is described. Raid is a message-passing system, with server processes on each site. The servers manage concurrent processing, consistent replicated copies during site failures and atomic distributed commitment. A high-level, layered communications package provides a clean, location-independent interface between servers. The latest design of the communications package delivers messages via shared memory in a high-performance configuration in which several servers are linked into a single process. Raid provides the infrastructure to experimentally investigate various methods for supporting reliable distributed transaction processing. Measurements on transaction processing time and server CPU time are presented. Data and conclusions of experiments in three categories are also presented: communications software, consistent replicated copy control during site failures, and concurrent distributed checkpointing. A software tool for the evaluation of transaction processing algorithms in an operating system kernel is proposed     

Design of a distributed CODASYL database system

A general model for distributed database systems based on the three-level architecture is presented. How concrete architectural forms can be derived from the general model is illustrated by means of the CODASYL database model. A new language is introduced, the data partition language, in which all distribution specific statements are concentrated. The application of distribution predicates in the data partition language to form distribution units leads to the concept of a “distribution graph”—it is a subset of the schema graph and defines the validity scope of a distribution predicate. Global database keys, global currency indicators and multiple record access are suggested to manipulate distributed CODASYL databases.     

分布式数据库在商业供应链系统中的应用

随着网络中数据库应用的发展,使得分布式数据库的应用领域得到快速的扩展。针对商业流通企业大规模、分散式经营以及集团化管理的模式,提出了在商业供应链系统中采用分布式数据库的结构设计方案,对供应链系统的数据库体系进行了分析,对在数据库设计过程中的一些关键问题进行探讨并给出了解决方法。以Oracle 9i数据库系统为例,介绍了采用增量复制、分组、半连接技术,进行数据复制、解决数据冲突以及进行查询优化的实现方法。     

分散型系统中分布式数据库的建立和维护

本文叙述分散型系统的分布式数据库的建立和维护，说明了系统数据库的关系模式，讨论了数据库在内存中的组织形式，并叙述了它们在系统中的建立和维护方法。     

Mariposa: a wide-area distributed database system

The requirements of wide-area distributed database systems differ dramatically from those of local-area network systems. In a wide-area network (WAN) configuration, individual sites usually report to different system administrators, have different access and charging algorithms, install site-specific data type extensions, and have different constraints on servicing remote requests. Typical of the last point are production transaction environments, which are fully engaged during normal business hours, and cannot take on additional load. Finally, there may be many sites participating in a WAN distributed DBMS. In this world, a single program performing global query optimization using a cost-based optimizer will not work well. Cost-based optimization does not respond well to site-specific type extension, access constraints, charging algorithms, and time-of-day constraints. Furthermore, traditional cost-based distributed optimizers do not scale well to a large number of possible processing sites. Since traditional distributed DBMSs have all used cost-based optimizers, they are not appropriate in a WAN environment, and a new architecture is required. We have proposed and implemented an economic paradigm as the solution to these issues in a new distributed DBMS called Mariposa. In this paper, we present the architecture and implementation of Mariposa and discuss early feedback on its operating characteristics. Edited by Henry F. Korth and Amith Sheth. Received November 1994 / Revised June 1995 / Accepted September 14, 1995     

The effect of a database feedback system on user performance

Abstract

There are two main approaches to improving the effectiveness of database interfaces. One is to raise the level of abstraction for the content of the user-database interaction. The relational model belonging to the logical level has replaced the hierarchical and network models that belong to the lower physical level. It is likely that the relational model will eventually be replaced by models belonging to the even higher conceptual level, such as entity relationship models and object-oriented models. The second approach is to enhance the actual interaction process. This can be done by providing better feedback to the user. Feedback can be in the form of more comprehensible error messages, and the provision of a natural language interpretation of user's query. Such a feedback system was developed, and its effectiveness tested in an experiment. The results showed that the feedback system enhanced user performance greatly. Specifically, users who used the feedback system were 12.9% more accurate than those without the feedback system. They were also 41.2% more confident of their answers, and they took 29.0% less time than those without the feedback system.     

The effect of a database feedback system on user performance

There are two main approaches to improving the effectiveness of database interfaces. One is to raise the level of abstraction for the content of the user-database interaction. The relational model belonging to the logical level has replaced the hierarchical and network models that belong to the lower physical level. It is likely that the relational model will eventually be replaced by models belonging to the even higher conceptual level, such as entity relationship models and object-oriented models. The second approach is to enhance the actual interaction process. This can be done by providing better feedback to the user. Feedback can be in the form of more comprehensible error messages, and the provision of a natural language interpretation of user's query. Such a feedback system was developed, and its effectiveness tested in an experiment. The results showed that the feedback system enhanced user performance greatly. Specifically, users who used the feedback system were 12.9% more accurate than those without the feedback system. They were also 41.2% more confident of their answers, and they took 29.0% less time than those without the feedback system.     

面向电力调度系统的分布式数据库管理系统的设计

针对电力实时信息网的实时性和地理上的分散性给信息交换带来的困难,提出基于分布式数据库体系结构的电力实时数据共享的解决方案。     

Microcomputers and distributed database management systems

The role of a DDBMS is to provide overall system integrity, appropriate data access, and recovery over the whole network. Many of the supermicros with powerful 16 and 32 bit architectures will soon be running advanced DBMS and DDBMS software, thus, playing an important role as a distributed database on a network. The article discusses this and future trends.     

A performance evaluation of distributed database architectures

The globally integrated contemporary business environment has prompted new challenges to database architectures in order to enable organizations to improve database applications performance, scalability, reliability and data privacy in adapting to the evolving nature of business. Although a number of distributed database architectures are available for choice, there is a lack of an in‐depth understanding of the performance characteristics of these database architectures in a comparison way. In this paper, we report a performance study of three typical (centralized, partitioned and replicated) database architectures. We used the TPC‐C as the evaluation benchmark to simulate a contemporary business environment, and a commercially available database management system that supports the three architectures. We compared the performance of the partitioned and replicated architectures against the centralized database, which results in some interesting observations and practical experience. The findings and the practice presented in this paper provide useful information and experience for the enterprise architects and database administrators in determining the appropriate database architecture in moving from centralized to distributed environments. Copyright © 2012 John Wiley & Sons, Ltd.     

Transaction management in distributed heterogeneous database management systems

Current distributed, heterogeneous database management systems (DBMSs) address the issue of distributed transaction management (DTM) in two different ways: some systems rely solely on unmodified local transaction managers (LTMs), thereby helping preserve local DBMS autonomy, but limit functionality (e.g. allow only unsynchronized retrievals, preclude distributed updates, etc.); others maintain full functionality but require the (re)design of the LTMs to enforce homogeneous DTM across all heterogeneous DBMSs, thereby giving up most of the local DBMS autonomy.

The goal of the work presented here is to establish the minimum set of modifications to LTMs that allow synchronized retrievals and distributed updates (whenever semantic conflicts can be resolved), and will continue to maintain a high degree of local DBMS autonomy. The problems of: (1) distribution of responsibility between DTM and LTMs, (2) concatenation of functionally-equivalent LTM mechanisms, and (3) providing compensation mechanisms for functionally-limited LTMs are introduced. Solutions to the above problems are shown to exist. However, the interconnection of autonomous, heterogeneous DBMSs is significantly more difficult than anticipated, despite communication standardization and current optimism.     

Process model and resource management in a distributed database

A deadlock-free resource management for a homogeneous distributed database system is proposed. Consistent database access is guaranteed in sections called transactions. Transactions consist of several processes of hierarchical structure. Transactions with read-and write-operations use a two-phase locking. The read-resources are locked as they are needed. The write-operations are buffered and executed at the end of a transaction. At this point the write-resources can be locked in a given order. Transactions which only read the database, do not lock the resources. It is only checked if these transactions can be serialized. Conflicts are resolved by resetting of transactions. No expensive recovery is needed. No physical controlling centre is used.     

Design and Implementation of a Heterogeneous Distributed Database System

This paper introduces a heterogeneous distributed database system called LSZ system,where LSZ is an abbreviation of Li Shizhen,an ancient Chinese medical scientist.LSZ system adopts cluster as distributed database node(or site).Each cluster consists of one of several microcomputers and one server.Te paper describes its basic architecture and the prototype implementation,which includes query processing and optimization,transaction manager and data language translation.The system provides a uniform retrieve and update user interface through global relational data language GRDL.     

一种基于扩充相容性封锁的多版本两阶段封锁协议

分析了现有的分布式并发控制机制的不足,提出一种基于有序相容性多粒度的多版本两阶段封锁协议,并对其正确性进行了证明。分析表明,该协议可有效提高协作设计事务的并发度,比较适合于开放式的协同设计环境。