Atomic broadcast and failure detection are powerful primitives for distributed database systems. In the distributeddatabase system LAMBDA, they are provided as network primitives. In this paper, we show how atomic br...
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Data fragmentation technique improves the performance of the system throughput and reduces the amount of irrelevant data to be accessed and transferred among different sites in distributed database systems (DDBs). We ...
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ISBN:
(纸本)9781932415605
Data fragmentation technique improves the performance of the system throughput and reduces the amount of irrelevant data to be accessed and transferred among different sites in distributed database systems (DDBs). We propose a database fragment generating method that splits the database relations into pair-wise disjoint fragments, which would be allocated to the DDBs sites during the process of allocation. This method guarantees the ability of processing a given portion of a given transaction in all sites, and improves the query processing performance by minimizing the fragments access cost. We developed an interactive interface application based on our proposal method to generate the application segments, and produce the minimum number of fragments. Some results in tabular and graphical means will be presented to demonstrate the efficiency of the method.
Site failures and network partitioning affect transaction processing in distributed database systems. A system is resilient to certain failures if transaction processing can continue even in the presence of those fail...
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Replication is a key factor in improving data availability in distributedsystems. Replicated data is stored redundantly at multiple sites so that it can be used by transactions even when some of the copies are not av...
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The reliability of a distributed database systems is the probability that a program which runs on multiple processing elements and needs to communicate with other processing elements for remote database will be execut...
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The reliability of a distributed database systems is the probability that a program which runs on multiple processing elements and needs to communicate with other processing elements for remote database will be executed successfully. This reliability varies according to 1) the topology of the distributeddatabase system, 2) the reliability of the communication links, 3) the databases and program distribution among processing elements, and 4) the databases required to execute a program. This paper shows that solving this reliability problem is NP-hard even when the distributeddatabase system is restricted to a series-parallel, a 2-tree, a tree, or a star structure. Two polynomial-time algorithms are proposed for computing the reliability of a distributed program which runs on a linear and a ring distributeddatabase system, respectively.
Deadlock detection and resolution is one of the major component of a successful distributeddatabase management system. In this paper, we discuss deadlock detection and resolution strategies and present two approaches...
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ISBN:
(纸本)9780897918121
Deadlock detection and resolution is one of the major component of a successful distributeddatabase management system. In this paper, we discuss deadlock detection and resolution strategies and present two approaches for detecting and resolving deadlocks in both general distributed database systems and in distributed real-time databasesystems. Our first approach is to collect information on connectivity of nodes of the overall Transaction Wait-For Graph (TWFG) of the distributeddatabase system and then use these connectivities information to build a local TWFG at each node of the overall TWGF. We then detect the deadlocks by locating the cycles in each local TWFG. To resolve the deadlocks the nodes involved in those cycles in each local TWFG, are removed until there is no cycle in the local TWFGs. Our second approach continuously checks for the occurrences of a deadlock between different transaction trees. As soon as it detects a deadlock it resolves it by aborting one of the transaction tree which has been initiated more recently. Some of the advantages of our approaches over the approaches which are using Probe messages are: (1) no extra storage required to store different probe messages, (2) no false (Phantom) deadlocks are reported, (3) detects and resolve all deadlocks. In addition, our approaches use less messages and time to detect and resolve all deadlocks in the existing TWFG of the distributed database systems.
In a database system supporting a real-time application, each transaction is associated with a timing constraint, typically in the form of a deadline. Replicated databasesystems possess desirable features for real-ti...
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ISBN:
(纸本)0897916344
In a database system supporting a real-time application, each transaction is associated with a timing constraint, typically in the form of a deadline. Replicated databasesystems possess desirable features for real-time applications, such as a high level of data availability, and potentially improved response time for queries. On the other hand, multiple copy updates lead to a considerable overhead due to the communication required among the data sites holding the copies. In this paper, we investigate the impact of storing multiple copies of data on satisfying the timing constraints of real-time transactions. A detailed performance model of a distributeddatabase system is employed in evaluating the effects of various workload parameters and design alternatives on the system performance. The performance is expressed in terms of the fraction of satisfied transaction deadlines.
Caching methods can be used for single query optimization and for multi-query optimization. Cost of evaluation can be reduced by exploiting common subexpressions and maintaining intermediate data structure. In this pa...
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A significant body of literature is available on distributed transaction commit protocols. Surprisingly, however, the relative merits of these protocols have not been studied with respect to their quantitative impact ...
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A significant body of literature is available on distributed transaction commit protocols. Surprisingly, however, the relative merits of these protocols have not been studied with respect to their quantitative impact on transaction processing performance. In this paper, using a detailed simulation model of a distributeddatabase system, we profile the transaction throughput performance of a representative set of commit protocols. A new commit protocol, OPT, that allows transactions to `optimistically' borrow uncommitted data in a controlled manner is also proposed and evaluated. The new protocol is easy to implement and incorporate in current systems, and can coexist with most other optimizations proposed earlier. For example, OPT can be combined with current industry standard protocols such as Presumed Commit and Presumed Abort. The experimental results show that distributed commit processing can have considerably more influence than distributed data processing on the throughput performance and that the choice of commit protocol clearly affects the magnitude of this influence. Among the protocols evaluated, the new optimistic commit protocol provides the best transaction throughput performance for a variety of workloads and system configurations. In fact, OPT's peak throughput is often close to the upper bound on achievable performance. Even more interestingly, a three-phase (i.e., non-blocking) version of OPT provides better peak throughput performance than all of the standard two-phase (i.e., blocking) protocols evaluated in our study.
In database applications, application programs are performed on clients and issue requests to object servers. Then, the object servers send responses to the clients. On the other hand, programs named agents move to ob...
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