• The Transactions of the Korea Information Processing Society
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• v.3 no.4
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• pp.791-802
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• 1996

In this paper, we discuss a distributed shared memory management scheme based on multi-threaded programming model for a large-scale loosely coupled multiprocessor system. The scheme covers three major issues in the distribued shared memory;the address translation table management, the block coherence maintenance, and the block placement policy. The scheme efficiently resolves the general problems occurred in the distributed shared memory such as a false sharing, an unnecessary replication, a block bouncing, and an address aliasing phenomenon. It also provides the application transparency, good scalability, easy implementation, and multithreaded programming model to users.

• Proceedings of the IEEK Conference
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• 2003.11b
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• pp.3-6
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• 2003

In this paper, we conduct a performance analysis for the composite scheme that is obtained by combining the data distribution and the data replication schemes usually used for the implementation of distributed directory service systems. The analysis results reveal that the composite model is a viable option to overcome the performance trade-off between the data distribution and the data replication model. In this paper, we present the performance model developed for the composite model by appling queuing modelling. Using the performance model, performance values for a variety of system execution environments are suggested which enable us to bring an efficient design for high performance distributed directories.

• Proceedings of the Korean Society of Computer Information Conference
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• 2014.07a
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• pp.337-340
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• 2014

클라우드 시스템이 큰 이슈로 떠오르면서 그 기반이 되는 분산 파일 시스템에 관한 연구가 계속되고 있다. 최근 제안된 분산파일 시스템은 대부분 확장 가능하며 신뢰성이 있는 시스템으로 구성되어 있으며 내고장성(Fault tolerance)과 높은 가용성을 위해 데이터 복제 기법을 사용하며 하둡 분산 파일 시스템에서는 블락의 복제수를 기본3개로 지정한다. 그러나 이 정책은 복제수가 많아지면 많아질수록 가용성은 높아지지만 스토리지 또한 증가한다는 단점이 있다. 본 논문에선 이러한 문제점을 해결하기 위해 최소한의 블락 복제수와 복제된 블락을 효율적으로 배치하여 더 좋은 성능과 부하분산(Load Balancing)하기 위한 기법을 제안한다.

• Journal of KIISE:Information Networking
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• v.29 no.3
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• pp.265-275
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• 2002

A default server strategy is a very popular scheme for managing location and state information of mobile hosts in cellular networks. But the communication cost increases if the call requests are frequent and the distant between the default server and the client is long. Still more any connection to a mobile host cannot be established when the default server of the destination mobile host fails. These problems can be solved by replicating default server and by letting nearest replicated default server process the query request which is sent from a client. It is important to allocate replicated default servers efficiently in networks and determine the number of replicated default servers. In this paper, we suggest and evaluate a default server replication strategy to reduce communication costs and to improve service availabilities. Furthermore we propose and evaluate an optimized allocation algorithm and an optimal replication degree for replicating: dofault servers in nn grid networks and binary tree networks.

• The Transactions of the Korea Information Processing Society
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• v.3 no.3
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• pp.631-639
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• 1996

In this paper we discuss the elements which must be considered for collaboration- aware application design and their effcets on user interfaces. Collaboration-aware applications have inter-user and user/system interaction features besides generic real-time distribution system features and this restricts the design freedom with the requirement of consistent user interfaces. Programmers, therefore, must provide uniform and logically consistent user interfaces to user and, for this end, they should consider main design features such as concurrency control algorithms, system topology and object replication scheme. Among the design factors concurrency control algorithms have relatively significant impact on user interfaces and we consider the impact of concurrency control agorithms along with that of thesystem to pologyand the objectreplication scheme. Coshed/SAS, a groupeditor, is given as an example of application of the factors.

• Journal of the Korean Operations Research and Management Science Society
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• v.21 no.1
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• pp.31-50
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• 1996

In this paper we prescribe a replication server scheme with an algorithm DRF (Differential Refresh File) to refresh multiple materialized views and replicas in distributed environments. Before sending relevant tuples in server sites to client sites, an effective tuple reduction scheme is developed as a preprocessor to reduce the transmission cost. Because it utilizes differential files with out touching base relations, the DRF scheme can help to minimize the number of locks, which enhances the system's performance.

• Proceedings of the Korean Information Science Society Conference
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• 2006.06d
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• pp.124-126
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• 2006

Mobile Ad hoc networking is an emerging technology and in these days many applications are being developed to run on these networks. In these networks lookup services are very important because all nodes do not have same resources in term of memory and computing power. Nodes need to use different services offered by different servers. Reliable and efficient scheme should be available for lookup services due to limited bandwidth and low computing power of devices in mobile ad hoc networks. Due to mobility and rapid change in network topology, lookup mechanism used in wired network is not appropriate. Service discovery mechanism can be divided into two main categories Centralized and Distributed. Centralized mechanism is not reliable as there is no central node in these networks. Secondly centralized mechanism leads toward single point failure. We can handle the service discovery mechanism by distributing server's information to each node. But this approach is also not appropriate due to limited bandwidth and rapid change in network. In this paper, we present reliable lookup service scheme which is based on distributed mechanism. We are not using replication approach as well due to low bandwidth of wireless networks. In this scheme service discovery mechanism will be handled through different lookup servers. Reliability is the key feature of our proposed scheme.

• Journal of Internet Computing and Services
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• v.17 no.4
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• pp.1-9
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• 2016

Algorithms implementing distributed shared memory (DSM) were developed for ensuring consistency. The performance of DSM algorithms is dependent on system and usage parameters. However, ensuring these algorithms to tolerate faults is a problem that needs to be researched. In this study, we proposed fault-tolerant scheme for DSM system and analyzed reliability and fault-tolerant overhead. Using our analysis, we can choose a proper algorithm for DSM on error prone environment.

• Proceedings of the Korean Information Science Society Conference
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• 1999.10c
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• pp.748-750
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• 1999

본 논문에서 우리는 통신 비용과 데이터베이스 비용을 감소시키기 위해 사용자 프로파일 복제본을 이용한 동적 위치 관리 기법을 제안한다. 이 기법에서는 위치등록과 호 설정 과정이 통신비용을 감소시킬 수 있는 복제본이 있는 VLR에서 수행되고, 복제본이 있는 VLR에서 호의 빈도커서 데이터베이스 비용을 감소시킨다. 제안한 기법의 성능을 분석하기 위해 분석 모델을 작성하고 제안 기법, IS-41 기법, 복제 기법의 성능 분석을 한다. 사용된 비교 척도는 통신 비용, 데이터 베이스 비용, 총비용 그리고 호 설정 지연이다. 이 척도들에 대해서 제안 기법이 IS-41 기법, 복제 기법보다 더 좋은 성능을 보인다.

• Journal of Computing Science and Engineering
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• v.11 no.3
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• pp.92-99
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• 2017

Memcached, commonly used to speed up the data access in big-data and Internet-web applications, is a system software of the distributed-cache mechanism. But it is subject to the severe challenge of the loss of recently uncommitted updates in the case where the Memcached servers crash due to some reason. Although the replica scheme and the disk-log-based replay mechanism have been proposed to overcome this problem, they generate either the overhead of the replica synchronization or the persistent-storage overhead that is caused by flushing related logs. This paper proposes a scheme of backing up the write requests (i.e., set and add) on the Memcached client side, to reduce the overhead resulting from the making of disk-log records or performing the replica consistency. If the Memcached server fails, a timestamp-based recovery mechanism is then introduced to replay the write requests (buffered by relevant clients), for regaining the lost-data updates on the rebooted Memcached server, thereby meeting the data-consistency requirement. More importantly, compared with the mechanism of logging the write requests to the persistent storage of the master server and the server-replication scheme, the newly proposed approach of backing up the logs on the client side can greatly decrease the time overhead by up to 116.8% when processing the write workloads.