• Journal of the Korea Society for Simulation
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• v.19 no.3
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• pp.91-98
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• 2010

This paper is on the research result for analyzing the performance of GLORY(GLobal Resource management sYstem) used for Web Server Cluster system, which was developed at ETRI(Electronic and Telecommunication Research Institute). The paper includes the definition of Web Server Cluster System, the characteristics of the system, user oriented system performance, current performance enhancement methods, computer simulation model for GLORY and its experimental results for the performance of GLORY. GLORY is composed of 2048~1,000,000 units of PCs, and is used for Internet servers. From the results of the simulation experiments, we notice that GLORY has enough capacity to fully serve the appropriate level of Internet services. Also, the results show that Web server service time is longer than that for network transmission time but requires more DNS than expected, and that 100Mbps LAN is good enough for directly connecting Internet to the Web servers while not affecting the total system performance.

• Journal of KIISE:Computer Systems and Theory
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• v.34 no.9
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• pp.435-444
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• 2007

Caching web pages is an important part of web infrastructures. The effects of caching service are even more pronounced for wireless infrastructures due to their limited bandwidth. Medium to large-scale infrastructures deploy a cluster of servers to solve the scalability problem and hot spot problem inherent in caching. In this paper we present scheduling scheme based on cache utilization in a wireless internet proxy server cluster environment. The proposed method uses cache utilization for distributing evenly client requests to a cluster of cache servers and solving hot spot problem. We have implemented our approach and performed various experiments using publicly available traces. Experimental results on a cluster of 16 cache servers demonstrate that the proposed hashing method gives 45% to 114% Performance improvement over other widely used methods while addressing the hot spot problem.

• Journal of Internet Computing and Services
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• v.6 no.2
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• pp.69-84
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• 2005

As the Internet users are increasing rapidly, a cluster web server system is attracted by many researchers and Internet service providers. The cluster web server has been developed to efficiently support a larger number of users as well as to provide high scalable and available system. In order to provide the high performance in the cluster web server, efficient load distribution is important, and recently many content-aware request distribution techniques have been proposed. In this paper, we propose a new content-aware load balancing technique that can evenly distribute the workload to each node in the cluster web server. The proposed technique is based on the hash histogram transformation, in which each URL entry of the web log file is hashed, and the access frequency and file size are accumulated as a histogram. Each user request is assigned into a node by mapping of (hashed value-server node) in the histogram transformation. In the proposed technique, the histogram is updated periodically and then the even distribution of user requests can be maintained continuously. In addition to the load balancing, our technique can exploit the cache effect to improve the performance. The simulation results show that the performance of our technique is quite better than that of the traditional round-robin method and we can improve the performance more than $10\%$ compared with the existing workload-aware load balancing(WARD) method.

• The KIPS Transactions:PartA
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• v.14A no.6
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• pp.371-382
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• 2007

Modern server systems are usually composed in the form of cluster systems in order to serve not only as many users but also as many kinds of applications as possible. The progression of the cluster system architecture leads in a middleware approach based on the Java framework. The middleware approach alleviates the efforts for the construction and the management of a server system but still preserves its performance and applications on the server. In this research, we introduce a new clustering scheme for the easy construction and maintenance of a cluster server system with the Java Management Extensions. We first demonstrate the construction and configuration process. Our experiment sets can verify that it is easy to construct, expand and manage a middleware based cluster system as well as the applications which reside on it. In addition, we can achieve reasonable performance on our service oriented clustered system with the help of state-of-the-art middleware. The experimental results of performance demonstration contain the availability of a server, and the effectiveness of load balancing and scheduling mechanisms. Especially, our service oriented scheduling mechanism was shown to successfully manage load imbalance under the normal load and cope with the overloaded situations, compared with other known scheduling mechanisms.

• Journal of the Korea Society for Simulation
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• v.12 no.4
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• pp.103-111
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• 2003

A distributed sewer cluster system is a cost-effective system to provide a service application for clients with reliable, scalable, available, and fault-tolerant features. In order to provide high quality services, it is necessary to evaluate service performances, tune the server system, and analyze performances. In this paper, we propose a simulator to generate workloads based on statistic configuration according to estimated application traffics, apply workload scheduling algorithms, and evaluate the simulation results. We introduce the simulator design modelling and architecture. By using flexible parameters, the simulator is able to generate various patterns of workloads with different statistics, and configure system environments such as the number of server nodes, system resources considered, and their capacities. With this simulator, we introduce two scenarios: one is to find appropriate thresholds for the best performance of cluster system, and the other is to find the suitable scheduling algorithm for workload characteristics of service applications.

• Journal of Advanced Navigation Technology
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• v.13 no.5
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• pp.669-676
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• 2009

HTTP or audio/video streaming services are good candidates for future centralized navigation system and in order to provide stability for such services, service providers use a cluster of web servers. In this paper, we provide the criteria for web server cluster design of vehicular users with consideration of differentiated access per different user classes. Several feasible scenarios are examined and their performance analysis using queueing theory is presented to provide the foundation for web server cluster design using traffic load balancer. Through the thorough analysis, efficient criteria for traffic load balancer design is derived. In order to satisfy users' service requirements, priority services controlled by traffic load balancer are considered and analyzed. We also provide the evaluation of the accuracy of the analytical model through simulation.

• KIPS Transactions on Computer and Communication Systems
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• v.2 no.7
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• pp.283-292
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• 2013

In order to ensure high performance, all the servers in an existing server cluster are always On regardless of number of real-time requests. They ensure QoS, but waste server power if some of them are idle. To save energy consumed by servers, the server power mode control was developed by shutdowning a server when a server is not needed. There are two types of server power mode control depending on when a server is actually turned off if the server is selected to be off: static or dynamic. In a static mode, the server power is actually turned off after a fixed time delay from the time of the server selection. In a dynamic mode, server power is actually turned off if all the services served in the server are done. This corresponds to a turn off after a variable time delay. The static mdoe has disadvantages. It takes much time to find an optimal shutdown time manually through repeated experiments. In this paper, we propose a dynamic shutdown method to overcome the disadvantages of static shutdown. The proposed method allows to guarantee user QoS with good power-saving because it automatically approaches an optimal shutdown time. We performed experiments using 30 PCs cluster. Experimental results show that the proposed dynamic shutdown method is almost same as the best static shutdown in terms of power saving, but better than the best static shutdown in terms of QoS.

• Journal of information and communication convergence engineering
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• v.3 no.2
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• pp.93-95
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• 2005

In order to create security session, security keys are preconfigured between communication objects. For this purpose, Handshake Protocol exists. The pre-master secret key that is used in this process needs to interpreted by a server to create master secret key, whose process requires a big calculation, resulting in deteriorating system's transmission performance. Therefore, it is helpful in increasing transmission speed to reuse secret keys rather than to create them at every connection.

• The KIPS Transactions:PartC
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• v.16C no.3
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• pp.363-372
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• 2009

For large scale VOD service, cluster servers are spotlighted to their high performance and low cost. A cluster server usually consists of a front-end node and multiple back-end nodes. Though increasing the number of back-end nodes can result in the more QoS streams for clients, the possibility of failures in back-end nodes is proportionally increased. The failure causes not only the stop of all streaming service but also the loss of the current playing positions. In this paper, when a back-end node becomes a failed state, the recovery mechanisms are studied to support the unceasing streaming service. For the actual VOD service environment, we implement a cluster-based VOD servers composed of general PCs and adopt the parallel processing for MPEG movies. From the implemented VOD server, a video block recovery mechanism is designed on parity algorithms. However, without considering the architecture of cluster-based VOD server, the application of the basic technique causes the performance bottleneck of the internal network for recovery and also results in the inefficiency CPU usage of back-end nodes. To address these problems, we propose a new failure recovery mechanism based on the pipeline computing concept.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.1
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• pp.251-259
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• 2000

As a server dependency for the availability and scalability becomes very important, the need for solid server providing non-stop workload have been increased. So, this paper describes a server configuration method for the availability and scalability. For the validity check of this paper, socket application and cluster resource DLL and administration DLL for the application are implemented and tested. 8y relocating the individual failed services from one sewer to another with the microsoft cluster sewer, it was confirmed the feasibility. The result showed that allowed applications on the original server to continue running, unaffected by the failed service.