Load sharing in distributed computer systems

PhD ThesisIn this thesis the problem of load sharing in distributed computer systems is investigated. Fundamental issues that need to be resolved in order to implement a load sharing scheme in a distributed system are identified and possible solutions suggested. A load sharing scheme has been designed and implemented on an existing Unix United system. The performance of this load sharing scheme is then measured for different types of programs. It is demonstrated that a load sharing scheme can be implemented on the Unix United systems using the existing mechanisms provided by the Newcastle Connection, and without making any significant changes to the existing software. It is concluded that under some circumstances a substantial improvement in the system performance can be obtained by the load sharing scheme.Science and Engineering Research Counci

Load Balancing via Random Local Search in Closed and Open systems

In this paper, we analyze the performance of random load resampling and migration strategies in parallel server systems. Clients initially attach to an arbitrary server, but may switch server independently at random instants of time in an attempt to improve their service rate. This approach to load balancing contrasts with traditional approaches where clients make smart server selections upon arrival (e.g., Join-the-Shortest-Queue policy and variants thereof). Load resampling is particularly relevant in scenarios where clients cannot predict the load of a server before being actually attached to it. An important example is in wireless spectrum sharing where clients try to share a set of frequency bands in a distributed manner.Comment: Accepted to Sigmetrics 201

Local control of multiple module converters with ratings-based load sharing

Multiple module dc-dc converters show promise in meeting the increasing demands on ef- ficiency and performance of energy conversion systems. In order to increase reliability, maintainability, and expandability, a modular approach in converter design is often desired. This thesis proposes local control of multiple module converters as an alternative to using a central controller or master controller. A power ratings-based load sharing scheme that allows for uniform and non-uniform sharing is introduced. Focus is given to an input series, output parallel (ISOP) configuration and modules with a push-pull topology. Sensorless current mode (SCM) control is digitally implemented on separate controllers for each of the modules. The benefits of interleaving the switching signals of the distributed modules is presented. Simulation and experimental results demonstrate stable, ratings-based sharing in an ISOP converter with a high conversion ratio for both uniform and non-uniform load sharing cases

Control of Distributed Uninterruptible Power Supply Systems

In the last years, the use of distributed uninterruptible power supply (UPS) systems has been growing into the market, becoming an alternative to large conventional UPS systems. In addition, with the increasing interest in renewable energy integration and distributed generation, distributed UPS systems can be a suitable solution for storage energy in micro grids. This paper depicts the most important control schemes for the parallel operation of UPS systems. Active load-sharing techniques and droop control approaches are described. The recent improvements and variants of these control techniques are presented

Load Sharing in Distributed Multimedia-on-Demand Systems

10.1109/69.846293IEEE Transactions on Knowledge and Data Engineering123410-428ITKE

Distributed PI-Control with Applications to Power Systems Frequency Control

This paper considers a distributed PI-controller for networked dynamical systems. Sufficient conditions for when the controller is able to stabilize a general linear system and eliminate static control errors are presented. The proposed controller is applied to frequency control of power transmission systems. Sufficient stability criteria are derived, and it is shown that the controller parameters can always be chosen so that the frequencies in the closed loop converge to nominal operational frequency. We show that the load sharing property of the generators is maintained, i.e., the input power of the generators is proportional to a controller parameter. The controller is evaluated by simulation on the IEEE 30 bus test network, where its effectiveness is demonstrated

A simple beam model for the shear failure of interfaces

We propose a novel model for the shear failure of a glued interface between two solid blocks. We model the interface as an array of elastic beams which experience stretching and bending under shear load and break if the two deformation modes exceed randomly distributed breaking thresholds. The two breaking modes can be independent or combined in the form of a von Mises type breaking criterion. Assuming global load sharing following the beam breaking, we obtain analytically the macroscopic constitutive behavior of the system and describe the microscopic process of the progressive failure of the interface. We work out an efficient simulation technique which allows for the study of large systems. The limiting case of very localized interaction of surface elements is explored by computer simulations.Comment: 11 pages, 13 figure

An evaluation of load sharing algorithms for heterogeneous distributed systems

Distributed systems offer the ability to execute a job at other nodes than the originating one. Load sharing algorithms use this ability to distribute work around the system in order to achieve greater efficiency. This is reflected in substantially reduced response times. In the majority of studies the systems on which load sharing has been evaluated have been homogeneous in nature. This thesis considers load sharing in heterogeneous systems, in which the heterogeneity is exhibited in the processing power of the constituent nodes. Existing algorithms are evaluated and improved ones proposed. Most of the performance analysis is done through simulation. A model of diskless workstations communicating and transferring jobs by Remote Procedure Call is used. All assumptions about the overheads of inter-node communication are based upon measurements made on the university networks. The comparison of algorithms identifies those characteristics that offer improved performance in heterogeneous systems. The level of system information required for transfer is investigated and an optimum found. Judicious use of the collected information via algorithm design is shown to account for much of the improvement. However detailed examination of algorithm behaviour compared with that of a 'optimum' load sharing scenario reveals that there are occasions when full use of all the information available is not beneficial. Investigations are carried out on the most promising algorithms to assess their adaptability, scalability and stability under a variety of differing conditions. The standard definitions of load balancing and load sharing are shown not to apply when considering heterogeneous systems. To validate the assumptions in the simulation model a load sharing scenario was implemented on a network of Sun workstations at the University. While the scope of the implementation was somewhat limited by lack of resources, it does demonstrate the relative ease with which the algorithms can be implemented without alteration of the operating system code or modification at the kernel level

Towards a Framework for DHT Distributed Computing

Distributed Hash Tables (DHTs) are protocols and frameworks used by peer-to-peer (P2P) systems. They are used as the organizational backbone for many P2P file-sharing systems due to their scalability, fault-tolerance, and load-balancing properties. These same properties are highly desirable in a distributed computing environment, especially one that wants to use heterogeneous components. We show that DHTs can be used not only as the framework to build a P2P file-sharing service, but as a P2P distributed computing platform. We propose creating a P2P distributed computing framework using distributed hash tables, based on our prototype system ChordReduce. This framework would make it simple and efficient for developers to create their own distributed computing applications. Unlike Hadoop and similar MapReduce frameworks, our framework can be used both in both the context of a datacenter or as part of a P2P computing platform. This opens up new possibilities for building platforms to distributed computing problems. One advantage our system will have is an autonomous load-balancing mechanism. Nodes will be able to independently acquire work from other nodes in the network, rather than sitting idle. More powerful nodes in the network will be able use the mechanism to acquire more work, exploiting the heterogeneity of the network. By utilizing the load-balancing algorithm, a datacenter could easily leverage additional P2P resources at runtime on an as needed basis. Our framework will allow MapReduce-like or distributed machine learning platforms to be easily deployed in a greater variety of contexts