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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

A comparative study of the performance of concurrency control algorithms in a centralised database

Ross, Donald Francis January 1988 (has links)
No description available.
2

Ensuring Serializable Executions with Snapshot Isolation DBMS

Alomari, Mohammad January 2009 (has links)
Doctor of Philosophy(PhD) / Snapshot Isolation (SI) is a multiversion concurrency control that has been implemented by open source and commercial database systems such as PostgreSQL and Oracle. The main feature of SI is that a read operation does not block a write operation and vice versa, which allows higher degree of concurrency than traditional two-phase locking. SI prevents many anomalies that appear in other isolation levels, but it still can result in non-serializable execution, in which database integrity constraints can be violated. Several techniques have been proposed to ensure serializable execution with engines running SI; these techniques are based on modifying the applications by introducing conflicting SQL statements. However, with each of these techniques the DBA has to make a difficult choice among possible transactions to modify. This thesis helps the DBA’s to choose between these different techniques and choices by understanding how the choices affect system performance. It also proposes a novel technique called ’External Lock Manager’ (ELM) which introduces conflicts in a separate lock-manager object so that every execution will be serializable. We build a prototype system for ELM and we run experiments to demonstrate the robustness of the new technique compare to the previous techniques. Experiments show that modifying the application code for some transactions has a high impact on performance for some choices, which makes it very hard for DBA’s to choose wisely. However, ELM has peak performance which is similar to SI, no matter which transactions are chosen for modification. Thus we say that ELM is a robust technique for ensure serializable execution.
3

Ensuring Serializable Executions with Snapshot Isolation DBMS

Alomari, Mohammad January 2009 (has links)
Doctor of Philosophy(PhD) / Snapshot Isolation (SI) is a multiversion concurrency control that has been implemented by open source and commercial database systems such as PostgreSQL and Oracle. The main feature of SI is that a read operation does not block a write operation and vice versa, which allows higher degree of concurrency than traditional two-phase locking. SI prevents many anomalies that appear in other isolation levels, but it still can result in non-serializable execution, in which database integrity constraints can be violated. Several techniques have been proposed to ensure serializable execution with engines running SI; these techniques are based on modifying the applications by introducing conflicting SQL statements. However, with each of these techniques the DBA has to make a difficult choice among possible transactions to modify. This thesis helps the DBA’s to choose between these different techniques and choices by understanding how the choices affect system performance. It also proposes a novel technique called ’External Lock Manager’ (ELM) which introduces conflicts in a separate lock-manager object so that every execution will be serializable. We build a prototype system for ELM and we run experiments to demonstrate the robustness of the new technique compare to the previous techniques. Experiments show that modifying the application code for some transactions has a high impact on performance for some choices, which makes it very hard for DBA’s to choose wisely. However, ELM has peak performance which is similar to SI, no matter which transactions are chosen for modification. Thus we say that ELM is a robust technique for ensure serializable execution.
4

Parallel discrete event simulation

Kalantery, Nasser January 1994 (has links)
No description available.
5

A FAMILY OF HIERARCHICAL CONCURRENCY CONTROL PROTOCOLS

Xiong, Weidong 01 August 2018 (has links)
In this thesis, we propose a family of concurrency control protocols for high data contention database environments. The first one is called the Prudent-Precedence Concurrency Control (PPCC) protocol. It is prudently more aggressive in permitting more serializable schedules than two-phase locking and maintains a restricted precedence among conflicting transactions and commits the transactions according to the serialization order established in the executions. The second one is a family of hierarchical concurrency control protocols called the Hierarchical Precedence Concurrency Control (HPCC) protocols. It maintains cycle-free precedence hierarchies for conflicting transactions. Conflicting operations are allowed to proceed only if the hierarchical orderings of precedence is not violated. Transactions also commit based on the serialization order established during the executions. Detailed simulation models have been implemented for all these protocols and extensive experiments have been conducted to evaluate the performance of the proposed approaches. The results demonstrate that the proposed algorithms outperform the two-phase locking and optimistic concurrency control over a wide range of system workloads.
6

A Study of Conflict Detection in Software Transactional Memory

Lupei, Daniel 15 February 2010 (has links)
Transactional Memory (TM) has been proposed as a simpler parallel programming model compared to the traditional locking model. However, uptake from the programming community has been slow, primarily because performance issues of software-based TM strategies are not well understood. In this thesis we conduct a systematic analysis of conflict scenarios that may emerge when enforcing correctness between conflicting transactions. We find that some combinations of conflict detection and resolution strategies perform better than others depending on the conflict patterns in the application. We validate our findings by implementing several concurrency control strategies, and by measuring their relative performance. Based on these observations, we introduce partial rollbacks as a mechanism for effectively compensating the variability in the TM algorithm performance. We show that using this mechanism we can obtain close to the overall best performance for a range of conflict patterns in a synthetically generated workload and a realistic game application.
7

A Study of Conflict Detection in Software Transactional Memory

Lupei, Daniel 15 February 2010 (has links)
Transactional Memory (TM) has been proposed as a simpler parallel programming model compared to the traditional locking model. However, uptake from the programming community has been slow, primarily because performance issues of software-based TM strategies are not well understood. In this thesis we conduct a systematic analysis of conflict scenarios that may emerge when enforcing correctness between conflicting transactions. We find that some combinations of conflict detection and resolution strategies perform better than others depending on the conflict patterns in the application. We validate our findings by implementing several concurrency control strategies, and by measuring their relative performance. Based on these observations, we introduce partial rollbacks as a mechanism for effectively compensating the variability in the TM algorithm performance. We show that using this mechanism we can obtain close to the overall best performance for a range of conflict patterns in a synthetically generated workload and a realistic game application.
8

Serializable Isolation for Snapshot Databases

Cahill, Michael James January 2009 (has links)
PhD / Many popular database management systems implement a multiversion concurrency control algorithm called snapshot isolation rather than providing full serializability based on locking. There are well-known anomalies permitted by snapshot isolation that can lead to violations of data consistency by interleaving transactions that would maintain consistency if run serially. Until now, the only way to prevent these anomalies was to modify the applications by introducing explicit locking or artificial update conflicts, following careful analysis of conflicts between all pairs of transactions. This thesis describes a modification to the concurrency control algorithm of a database management system that automatically detects and prevents snapshot isolation anomalies at runtime for arbitrary applications, thus providing serializable isolation. The new algorithm preserves the properties that make snapshot isolation attractive, including that readers do not block writers and vice versa. An implementation of the algorithm in a relational database management system is described, along with a benchmark and performance study, showing that the throughput approaches that of snapshot isolation in most cases.
9

'n Studie van 'n aantal gelyktydigheidsbeheerprotokolle vir databasisse

Kruger, Hanlie 18 March 2014 (has links)
M.Sc. (Computer Science) / Concurrency control is the problem that exists in a database management system when more than one transaction or application is executed simultaneously. If transactions or applications are executed sequentially there will- be no problem with the allocation of resources. It is however necessary to execute transactions concurrently to utilise computer and resource capacity to its maximum extent. It can lead to inconsistent data if this concurrent execution of transactions are not properly controlled. If this should happen the data would be of no more use to the users of a system. The thesis is divided in the following way. Chapter 1 gives background information on the concurrency control problem. In chapter 2 a couple of mechanisms for solving the concurrency control problem are studied briefly. Chapters 3 and 4 provides a more in depth study of two specific mechanisms namely two-phase locking and timestamps. 80th of these mechanisms have already been implemented in systems to. solve the concurrency control problem.- In chapter 5 a comparison is made of the two methods described in chapters 3 and 4. A third method for handling concurrency control is briefly described in chapter 6. This method hasn't received a lot of attention from researchers yet. And in the last chapter, chapter 7, the concurrency control method used in the SDD-1 system is studied in more detail. SDD-1 is a distributed database management system.
10

Software Considerations in the Control of Digital Communications Switching Systems

Ward, Ronald P. 10 1900 (has links)
International Telemetering Conference Proceedings / October 26-29, 1992 / Town and Country Hotel and Convention Center, San Diego, California / Today's complex implementations of integrated packet and circuit switched digital communications networks demand that the software used for controlling these systems be robust, fault tolerant, and capable of runtime recovery from all but the most severe of operational errors. The typical modern switched communications system includes the use of multiple circuit switches, each with potentially thousands of end-user interfaces. Further, these switches are often inter-connected to each other via high-capacity trunks. A single connection between two end-user interfaces often traverses a number of intermediate circuit switches in order to effect the end-to-end communications desired. In this complex, distributed environment, the establishment and dissolution of end-to-end user connections involve far more than simple binary connection states indicating the existence, or non-existence, of a link. More commonly, a single end-to-end connection requires multiple node links across multiple, heterogeneous interfaces. The command and control software used to establish, monitor, and dissolve these connections must be capable of dealing with errors which arise at any node along the way in a consistent and reliable manner. Most critically, the system software must be capable of maintaining an accurate, multi-level mapping of distributed resources' availability, allocation, and status. Further, the software must have the capability of "healing itself" during operational run-time when it can, and of accurately reporting the nature of inconsistencies caused by anomalous events that cannot be fixed on the fly. The Edwards Digital Switch (EDS), developed by CSTI, provides a case study of possible solutions, and potential pitfalls, that can arise in the design, development, and implementation of the controlling software in today's dynamic, distributed communications' system architectures.

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