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.     

Secure dynamic fragment and replica allocation in large-scale distributed file systems

We present a distributed algorithm for file allocation that guarantees high assurance, availability, and scalability in a large distributed file system. The algorithm can use replication and fragmentation schemes to allocate the files over multiple servers. The file confidentiality and integrity are preserved, even in the presence of a successful attack that compromises a subset of the file servers. The algorithm is adaptive in the sense that it changes the file allocation as the read-write patterns and the location of the clients in the network change. We formally prove that, assuming read-write patterns are stable, the algorithm converges toward an optimal file allocation, where optimality is defined as maximizing the file assurance.     

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.     

Multilevel security issues in distributed database management systems

This paper describes the security needs in a distributed processing environment common to many enterprises and discusses the applicability of multilevel secure database management systems in such an environment.     

A new dynamic voting algorithm for distributed database systems

We consider the problem of keeping a distributed database system that has been partitioned because of site or communication link failures partially operable while ensuring data consistency. A dynamic-voting-consistency algorithm is proposed, and its correctness is demonstrated. The proposed algorithm results in improved efficiency in executing read requests by not requiring a read quorum. This algorithm is effective in environments where the majority of user requests are “read” types of requests. Furthermore, the proposed algorithm results in efficient recovery by avoiding updating those data objects that are still current. Under the proposed algorithm, the majority partition would be available even if changes in the network topology take place at a higher rate than the update rate, as long as only simple partitioning takes place     

Four reference architectures for distributed database management systems

Five requirements for a centralized database management system and five additional requirements for a distributed database management system suggest definitions of software processors and schemas. These software processors and schemas can be organized into four reference architectures for distributed database management systems which permit comparisons of their advantages and disadvantages.     

Some notes on authorization and transaction management in distributed database systems

Two topics on distributed database systems, in which security is involved are treated.

• 1.(1)Authorization: the dynamical granting, checking and revocation of access privileges to permit users to share data on the one hand and to retain the possibility to restrict such privileges on the other hand.
• 2.(2)Transaction management: to control the execution of database actions comprising a transaction so that it is atomic and recoverable.

Included for both subjects is a survey of various problems arising in the area. Then algorithms to solve these problems are described. Distributed problems are very often more difficult than their non-distributed equivalents. Attention will be paid to how the algorithms deal with the distributed aspect.     

A new vertical fragmentation algorithm based on ant collective behavior in distributed database systems

Considering the existing massive volumes of data processed nowadays and the distributed nature of many organizations, there is no doubt how vital the need is for distributed database systems. In such systems, the response time to a transaction or a query is highly affected by the distribution design of the database system, particularly its methods for fragmentation, replication, and allocation data. According to the relevant literature, from the two approaches to fragmentation, namely horizontal and vertical fragmentation, the latter requires the use of heuristic methods due to it being NP-Hard. Currently, there are a number of different methods of providing vertical fragmentation, which normally introduce a relatively high computational complexity or do not yield optimal results, particularly for large-scale problems. In this paper, because of their distributed and scalable nature, we apply swarm intelligence algorithms to present an algorithm for finding a solution to vertical fragmentation problem, which is optimal in most cases. In our proposed algorithm, the relations are tried to be fragmented in such a way so as not only to make transaction processing at each site as much localized as possible, but also to reduce the costs of operations. Moreover, we report on the experimental results of comparing our algorithm with several other similar algorithms to show that ours outperforms the other algorithms and is able to generate a better solution in terms of the optimality of results and computational complexity.     

面向本地分布式存储系统的动态副本策略

针对本地分布式存储系统的拓扑结构与存储组成单元的特性,提出了一种基于频度的动态副本算法FBDR。FBDR分别采用基于密度的单次频度分析和基于区间长度的两次频度聚合的方法对文件访问流进行分析,作为确定热点文件的依据,具有较高的命中率。在副本创建位置选择上,综合考虑了存储单元的可用空间、负载、IO性能等因素,使热点文件获得更高的IO速率,同时兼顾了存储单元之间的负载与资源利用的平衡。     

Improving the flexibility for replicated data management in distributed database systems

This paper presents a novel scheme for implementing the flexible replica control protocol[13] in the distributed database systems. The scheme requires less nodes to be locked to perform the read(write) operations. This not only provides better performance, but also provides the system designer extra flexibility to implement the protocol.     

Security design in distributed database systems

This paper deals with data security design in a distributed environment. A goal of the paper is to present a multiphase security design methodology reflecting the current approach to data base design. The aggregated distributed environment is considered, and a multilevel logical security system architecture is examined. For each level the content of the security logical schemata is defined and described. Finally, mapping rules between the logical levels are presented.     

A dynamic replica management strategy in data grid

Data Grid provides scalable infrastructure for storage resource and data files management, which supports several large scale applications. Due to limitation of available resources in grid, efficient use of the grid resources becomes an important challenge. Replication is a technique used in data grid to improve fault tolerance and to reduce the bandwidth consumption. This paper proposes a Dynamic Hierarchical Replication (DHR) algorithm that places replicas in appropriate sites i.e. best site that has the highest number of access for that particular replica. It also minimizes access latency by selecting the best replica when various sites hold replicas. The proposed replica selection strategy selects the best replica location for the users' running jobs by considering the replica requests that waiting in the storage and data transfer time. The simulated results with OptorSim, i.e. European Data Grid simulator show that DHR strategy gives better performance compared to the other algorithms and prevents unnecessary creation of replica which leads to efficient storage usage.     

Organizational hurdles to distributed database management systems (DDBMS) adoption

Organizations adopt new technologies, ultimately, to enhance their competitive position and profitability. A distributed database management system (DDBMS) is an example of a technology that may enhance a company's profitability but is also likely to change the way it does business. Specifically, DDBMS adoption may disturb the locus of power, alter the organizational structure, and change the culture of a company. This exploratory study examines the organizational factors that influence the likelihood of DDBMS adoption. It identifies organizational hurdles to adoption, offers an agenda for research validation, and proposes strategies for overcoming the identified hurdles.     

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。     

Dynamic transaction routing in distributed database systems

The authors investigate dynamic transaction routing strategies for locally distributed database systems in which the database is partitioned and distributed among multiple transaction-processing systems, and the incoming transactions are routed by a common front-end processor. If a transaction issues a database request referencing a nonlocal database partition, the request has to be shipped to the system owing the referenced partition for processing. Various dynamic strategies are studied. Their performance is compared with that of the optimal static strategy. A class of dynamic transaction routing strategies which take into account routing history and minimize the estimated response time of incoming transactions is proposed; they are found to provide a substantial improvement over the optimal static strategy. The robustness of the strategies is further studied through sensitivity analysis over various transaction loads, communication overheads, and database reference distributions     

Analysis of replication in distributed database systems

The authors develop an approximate analytical model to study the tradeoffs of replicating data in a distributed database environment. Several concurrency control protocols are considered, including pessimistic, optimistic, and semi-optimistic protocols. The approximate analysis captures the effect of the protocol on hardware resource contention and data contention. The accuracy of the approximation is validated through detailed simulations. It is found that the benefit of replicating data and the optimal number of replicates are sensitive to the concurrency control protocol. Under the optimistic and semi-optimistic protocols, replications can significantly improve response time with an additional MIPS (million instructions per second) requirement to maintain consistency among the replicates. The optimal degree of replication is further affected by the transaction mix (e.g. the fraction of read-only transactions), the communications delay and overhead, the number of distributed sites, and the available MIPS. Sensitivity analyses have been carried out to examine how the optimal degree of replication changes with respect to these factors     

Divergence control for distributed database systems

This paper presents distributed divergence control algorithms for epsilon serializability for both homogeneous and heterogeneous distributed databases. Epsilon serializability allows for more concurrency by permitting non-serializable interleavings of database operations among epsilon transactions. We first present a strict 2-phase locking divergence control algorithm and an optimistic divergence control algorithm for a homogeneous distributed database system, where the local orderings of all the sub-transactions of a distributed epsilon transaction are the same. In such an environment, the total inconsistency of a distributed epsilon transaction is simply the sum of those of all its sub-transactions. We then describe a divergence control algorithm for a heterogeneous distributed database system, where the local orderings of all the sub-transactions of a distributed epsilon transaction may not be the same and the total inconsistency of a distributed epsilon transaction may be greater than the sum of those of all its sub-transactions. As a result, in addition to executing a local divergence control algorithm in each site to maintain the local inconsistency, a global mechanism is needed to take into account the additional inconsistency Recommended by: Meichum Hsu