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.     

Transaction processing in a peer to peer database network

This paper investigates a transaction processing mechanism in a peer to peer database network. A peer to peer database network is a collection of autonomous data sources, called peers, where each peer augments a conventional database management system with an inter-operability layer (i.e. mappings) for sharing data. In this network, each peer independently manages its database and executes queries as well as updates over the related data in other peers. In this paper, we consider a peer to peer database network where mappings between peers are established through data-level mappings for sharing data and resolving data heterogeneity. With regards to transaction processing in a peer to peer database network, we mainly focus on how to maintain a consistent execution view of concurrent transactions in peers without a global transaction coordinator. Since there is no global transaction coordinator and each peer executes concurrent transactions independently, different peers may produce different execution views for the same set of transactions. For this purpose, we investigate potential problems that arise when maintaining a consistent execution of concurrent transactions. In order to guarantee consistent execution, we introduce a correctness criteria and propose two approaches, namely Merged Transactions and OTM based propagation. We assume that one single peer initiates the concurrent transactions. We also present a solution for ensuring the consistent execution view of concurrent transactions considering the failures of transactions.     

移动数据库事务处理模型的研究

在移动数据库系统中,事务的移动性、频繁断接性以及长事务等特性使得传统的事务处理模式不再适用。提出一种扩展的乐观两阶段提交事务处理模型（O2PC-MT）,该模型吸收了O2PC-MT模型的设计思想,解决了由短暂的通信失效造成不必要的事务中止以及移动事务协调器故障导致的阻塞等问题。实验结果表明,与O2PC-MT事务处理模型相比,EO2PC-MT提高了系统的事务吞吐率以及改善了系统的总体性能。     

Commit protocols for externalized-commit heterogeneous database systems

In designing a heterogeneous database systems, one of the main technical challenges is developing techniques for ensuring global commit. That is, guaranteeing that a transaction spanning multiple individual database management systems (DBMSs) either commits at all the participating DBMSs or at none of them. Previous work in this area typically assumes that the participating DBMSs do not provide a mechanism for interacting with their commit facilities. While this is true in many cases, in practice there are systems which support a programmatic interface to their commit protocols. We refer to database systems offering such facilities asexternalized commit DBMSs.The focus of this paper is on commit protocols for these systems. We propose two new commit protocols for externalized commit DBMSs. The first may be used to obtain global commit in heterogeneous database systems composed of DBMSs with different 2-phase commit protocols (e.g., centralized and linear). The second protocol is more general, and ensures global commit even if the participating DBMSs employ 3-phase commit protocols. The more general protocol also preserves database autonomy, since it does not block a DBMS upon failure of another system. We describe both protocols in detail and prove their correctness. Recommended by: M. RusinkiewiczThis work was partially supported by an IBM Research Initiation Grant.     

Dealing with fuzziness in active mobile database systems

Current needs of industry required the development of advanced database models like active mobile database systems. An active mobile database system can be designed by incorporation of triggering rules into a mobile computing environment in which the users are able to access a collection of database services using mobile and non-mobile computers at any location. Fuzzy concepts are adapted to the field of databases in order to deal with ambiguous, uncertain data. Fuzziness comes into picture in active mobile databases especially with spatial queries on moving objects. Incorporating fuzziness into rules would also improve the effectiveness of active mobile databases as it provides much flexibility in defining rules for the supported application. In this paper we present some methods to adapt the concepts developed for fuzzy systems to active mobile databases.     

Concurrency control in mobile distributed real-time database systems

This paper presents DMVOCC-2PLV (Distributed Multiversion Optimistic Concurrency Control with Two-Phase Local Validation) protocol for processing mobile distributed real-time transactions in mobile broadcast environments. In DMVOCC-2PLV protocol, transaction validation is performed at two levels: local validation and global validation. Local validation of transactions is performed in two phases: local pre-validation and local final validation. At the MHs (Mobile Hosts), all mobile transactions perform local pre-validation of transactions by using a backward validation mechanism. The local pre-validation process is carried out against committed transactions at the server in the last broadcast cycle. Such an early data conflict detection feature can save processing and communication resources. Transactions that survive in local pre-validation must be submitted to the server for local final validation. In global validation distributed update transactions have to check to ensure distributed serializability in all participants. The protocol can eliminate conflicts between mobile read-only and mobile update transactions, and resolve data conflicts flexibly using multiversion dynamic adjustment of serialization order to avoid unnecessary restarts of transactions. Mobile read-only transactions can be committed with no-blocking, and respond time of mobile read-only transactions is greatly reduced. The tolerance of mobile transactions of disconnections from the broadcast channel is increased. The results of simulation experiment show that the new protocol proposed offers better performance in terms of miss rate, restart rate, commit rate and throughput.     

移动Agent在分布式异构数据库中的应用研究

移动Agent技术是新型的分布计算技术，它及其应用是目前国内外研究和开发的热点。基于CORBA(公共对象请求代理体系结构)和移动Agent，提出了一个解决多媒体异构数据库搜索的体系框架，它可以很好地解决数据传输瓶颈问题。这一框架的性能和可靠性比传统的客户／服务器方法有明显的提高。     

移动数据库的事务处理关键技术研究与分析

移动事务的移动性、频繁断接性等特点使传统的事务处理技术已不能适应移动环境,因此设计一个适应移动数据库环境的事务模型是移动事务处理关键.本文在分析移动事务的特点和移动事务处理典型结构基础上,主要论述设计移动事务模型必须要解决的移动事务的过区切换、断接处理、同步复制、故障恢复等四个关键技术的研究现状和原理分析.     

数据挖掘在常旅客系统中的应用

本文通过数据清洗和检查,数据整合,数据构造和数据整合等步骤进行数据处理,采用决策树分类方法进行分析,建立了一套对航空公司常旅客进行评价和监控的标准和方法.     

移动数据库中数据复制同步处理策略的研究

同步技术是保证复制移动数据库系统一致性的一项关键技术,鉴于目前移动复制同步技术存在通讯数据量大,存储空间消耗多,尤其是在网络带宽下降时,不能及时更新客户端的数据,导致移动事务执行失败等缺陷。通过UTLRSP（Union Transaction-Level Result-Set Propagation,关联事务结果集）复制同步模型结合数据广播技术,并利用基于优先级的增量更新算法实现客户端与中心数据库服务器的数据同步处理。实验结果表明,与两级复制机制相比,UTLRSP模型将事务作相关联处理,且只保存事务结果,有效降低了存贮空间的消耗,减小了同步过程中通讯数据量;基于优先级的增量更新算法根据数据新鲜度排列优先级,保证在无线网络带宽下降时新鲜度最高的数据先传输,提高了数据的传输效率、动态新鲜度以及客户端的可扩展性。     

Transaction multicasting scheme for resilient routing control in parallel cluster database systems

A disk cluster environment (DCE) refers to a distributed architecture for high performance transaction processing in which the computing nodes are locally coupled via a high-speed network and share a common database at the disk level. In the DCE, it is crucial to determine at which node the incoming transactions are processed. This is called transaction routing. The aim of disk sharing in DCE is not only to achieve high performance by distributing the workload among the processing nodes but also to obtain fault-tolerance against possible system failures, like a single node failure. Although a number of transaction routing schemes have been reported for DCE, it is true that most of them are not sufficiently resilient against system dynamics, which inevitably requires changing the routing information. In this paper, we propose a new dynamic transaction routing scheme for DCE, called multicast transaction routing scheme, MTR for short, that is able to change the transaction routing information in the presence of critical events without imposing too much overhead to the transaction processing system. In our scheme, when it is required to change the routing information dynamically, the routing algorithm sends multiple clones of a transaction to a group of candidate processing nodes and selects the processing node that first completes the multicasted transaction as a new processing node for re-routed transaction. The selected processing node is expected to be a best affinity node when the system load is evenly distributed, or a relatively unloaded processing node that is idle enough to process a transaction faster than other nodes. The novel aspect of MTR is that it automatically achieves an optimal balance between affinity-based routing and load balancing. The simulation study shows that MTR rapidly stabilizes the system and produces an optimal routing information so that it finally guarantees faster response time.     

Transaction pseudonyms in mobile environments

Network Operators start to offer formerly hidden services such as location service, messaging services and presence services. This fosters the development of a new class of innovative context aware applications that are operated by third party application providers. However, without the implementation of proper privacy protection mechanisms, location and presence information, that is processed by third party application providers, may also imply severe risks to users. If no privacy protection is foreseen, the user’s identity could be used maliciously which renders such applications dangerous. To protect the user’s sensitive data such as location information we propose a novel service architecture which fosters the development of innovative applications that brings together internet applications with telco services. An underlying privacy enhancing mechanism that is based on the notion of pseudonyms allows even untrusted third party application providers to access sensitive data provided by telco services such as location, presence or messaging services. Due to their high security, pseudonyms guarantee that the user’s identity is kept secret towards the untrusted application providers. Due to its low computational complexity this pseudonym generation scheme can also be implemented on devices such as mobile phones and digital assistants with only little computational power and restricted memory capabilities. To illustrate our approach, we demonstrate a transportation ticket application that implements the proposed service architecture. This application allows the use of transportation tickets which are extended by the location-tracking functionality. Similar to the well known paper based transportation tickets our solution supports anonymity of users even if the ticket application “knows” the location of the holder. Oliver Jorns is a researcher at the Telecommunications Research Center in Vienna and is also a Lecturer at the University of Vienna. Oliver Jung is employed as a Senior Researcher at the Telecommunications Research Center Vienna. He is also member of ISO/IEC JTC1 SC27 (IT security techniques). Gerald Quirchmayr is Professor at the Institute for Computer Science and Business Informatics at the University of Vienna and since January 2005 he heads the Department of Distributed and Multimedia Systems, Faculty of Computer Science, at the University of Vienna.     

移动主体异构资源互操作框架

随着Internet的发展,如何实现异构资源之间的互操作成为当前研究热点。要适应Internet这种开放、动态的环境,需要软件具有组件化、开放化、自主化等特点,而面向主体的软件开发方式则能满足这些需要。提出了一种基于移动主体（Mobile Agent）的异构资源互操作框架,用以实现异构数据源的整合,为用户提供统一信息检索服务。该框架为一多主体系统（Multi-Agent System）,为了实现主体间的通信和协作,设计了一种基于通用领域本体模型的主体通信机制。此外描述了该框架中移动主体的工作机制。     

A Transactional Asynchronous Replication Scheme for Mobile Database Systems

In mobile database systems,mobility of users has a significant impact on data replication.As a result,the various replica control protocols that exist today in traditional distributed and multidatabase environments are no longer suitable To solve this problem,a new mobile database replication scheme,the Transaction-Level Result-Set Propagation(TLRSP)model,is put forward in this paper,The conflict dectction and resolution strategy based on TLRSP is discussed in detail,and the implementation algorithm is proposed,In order to compare the performance of the TLRSP model with that of other mobile replication schemes,we have developed a detailde simulation model.Experimantal results show that the TLRSP model provides an effcient support for replicated mobile database systems by reducing reprocessing overhead and maintaining database consistency.     

FAST: Flash-aware external sorting for mobile database systems

Recently, flash memory has gained its popularity as storage on wide spectrum of computing devices such as cellular phones, digital cameras, digital audio players and PDAs. The integration of high-density flash memory has been accelerated twice every year for past few years. As flash memory’s capacity increases and its price drops, it is expected that flash memory will be more competitive with magnetic disk drives. Therefore, it is desirable to adapt disk-based algorithms to take advantage of the flash memory technology.In this paper, we propose a novel Flash-Aware external SorTing algorithm, FAST, that overcomes the limitation of larger writing cost for flash memory to improve both overall execution time and response time. In FAST, we reduce the write operations with additional read operations. We provide the analysis for both traditional and our flash-aware algorithms by comparing the detailed cost formulas. Experimental results with synthetic and real-life data sets show that FAST can result in faster execution time as well as smaller response time than traditional external sorting algorithms.     

基于主动数据库的移动P2P查询处理

提出了一个基于主动数据库的移动代理构造及管理系统模型。它采用主动数据库中的事件—条件—活动（ECA）规则来定义代理的逻辑结构并利用其触发器机制来实施代理的执行和管理，不仅大大简化了支持即时或连续查询的P2P系统的体系结构而且通过主动数据库的安全机制能确保从自治数据库中获取信息的安全性和有效性。给出了移动P2P系统中节点的体系结构，代理的结构、管理与生存周期并给出了一个应用实例。     

Job scheduler for streaming applications in heterogeneous distributed processing systems

The Journal of Supercomputing - In this study, we investigated the problem of scheduling streaming applications on a heterogeneous cluster environment and, based on our previous work, developed the...     

Efficient recursive XML query processing using relational database systems

Recursive queries are quite important in the context of XML databases. In addition, several recent papers have investigated a relational approach to store XML data and there is growing evidence that schema-conscious approaches are a better option than schema-oblivious techniques as far as query performance is concerned. However, the issue of recursive XML queries for such approaches has not been dealt with satisfactorily. In this paper we argue that it is possible to design a schema-oblivious approach that outperforms schema-conscious approaches for certain types of recursive queries. To that end, we propose a novel schema-oblivious approach, called Sucxent++ (Schema Unconcious XML Enabled System), that outperforms existing schema-oblivious approaches such as XParent by up to 15 times and schema-conscious approaches (Shared-Inlining) by up to eight times for recursive query execution. Our approach has up to two times smaller storage requirements compared to existing schema-oblivious approaches and 10% less than schema-conscious techniques. In addition Sucxent++ performs marginally better than Shared-Inlining and is 5.7–47 times faster than XParent as far as insertion time is concerned.     

Applications of object-oriented technology to the integration of heterogeneous database systems

The object-oriented paradigm has several features that facilitate the integration of heterogeneous data management systems. One of the main problems in the integration is to provide users with the same data model and language to access very different systems. This problem exists in all kinds of distributed heterogeneous data management systems, independently from their integration architecture (like classical distributed databases, federated databases, multidatabases). This paper shows that the use of an object-oriented data model for building a uniform view of several databases can greatly simplify this task, and actually extends the scope of integration towards two directions. The first concerns the integration of data management systems to which traditional integration techniques, based on mappings among data models, cannot be applied. The second direction moves the goal of integration to re-using not only data but to re-using data and application software using these data. In the paper we also briefly discuss some requirements for an object-oriented integrated platform. Recommended by: F. Manola