• Journal of KIISE
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• v.44 no.8
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• pp.767-773
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• 2017

In a distributed system environment, such as a cloud database, the tail latency needs to be kept short to ensure uniform quality of service. In this paper, through experiments on a Cassandra database, we show that long tail latency is caused by a lack of memory space because the database cannot receive any request until free space is reclaimed by writing the buffered data to the storage device. We observed that, since the performance of the storage device determines the amount of time required for writing the buffered data, the performance degradation of Solid State Drive (SSD) due to garbage collection results in a longer tail latency. We propose a garbage collection synchronization technique, called SyncGC, that simultaneously performs garbage collection in the java virtual machine and in the garbage collection in SSD concurrently, thus hiding garbage collection overheads in the SSD. Our evaluations on real SSDs show that SyncGC reduces the tail latency of $99.9^{th}$ and, $99.9^{th}-percentile$ by 31% and 36%, respectively.

• KIISE Transactions on Computing Practices
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• v.24 no.3
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• pp.129-137
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• 2018

NVMe(Non-Volatile Memory Express) SSD(Solid State Drive) is a high-performance storage that makes use of flash memory as a storage cell, PCIe as an interface and NVMe as a protocol on the interface. It supports multiple I/O queues which makes it feasible to process parallel-I/Os on multi-core environments and to provide higher bandwidth than SATA SSDs. Hence, NVMe SSD is considered as a next generation-storage for data-center and cloud computing system. However, in the virtualization system, the performance of NVMe SSD is not fully utilized due to the bottleneck of the software I/O stack. Especially, when it uses I/O stack of the hypervisor or the host operating system like Xen and KVM, I/O performance degrades seriously due to doubled-I/O stack between host and virtual machine. In this paper, we propose a new I/O engine, called Direct-AIO (Direct-Asynchronous I/O) engine, that can access NVMe SSD directly for I/O performance improvements on QEMU emulator. We develop our proposed I/O engine and analyze I/O performance differences between the existed I/O engine and Direct-AIO engine.

• Journal of Korea Multimedia Society
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• v.12 no.1
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• pp.41-49
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• 2009

Smart Card is currently more popular in mobile communication, and smart card with java card platform becomes a standard choice. Java card has a problem that it gets lost working data when power is off. Transaction is the idea to solve a problem of data loss, but it accepts only one transaction process, and other transaction process need to hold until the current working transaction is finished. This might be a factor to drop the Java card's performance. In this paper, we define a rule of dual-lock which can run transaction at multiple transaction buffer as a method for a better java card performance, and we suggest this rule to improve a capability of transaction process. From this research, we are able to improve the data stability, reduce the java card transaction delay time, and get a higher processing speed of java card.

• Journal of Advanced Navigation Technology
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• v.21 no.2
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• pp.206-211
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• 2017

Recently computing devices by connecting to a network, grid computing, the next generation of digital neural networks that provide maximum service will connect all of the computer such as a PC or server, PDA into one giant network makes the virtual machine. Therefore, we propose the grid computing implementation model to be applied to meteorological business field as follows. First, grid computing will be used for tasks such as the development of numerical models below the mid-scale or test operations, and the final backup of the weather supercomputer. Second, the resources that will constitute grid computing are limited to business PCs and Linux servers operated by the central government considering operational efficiency. Third, the network is restricted to the LAN section, which suggests the implementation of high performance computing.

• Journal of KIISE
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• v.45 no.2
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• pp.165-174
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• 2018

An online community is a virtual group whose members share their interests and hobbies anonymously with nicknames unlike Social Network Services. However, there are malicious user problems such as users who write offensive contents and there may exist data fragmentation problems in which the data of the same user exists in different nicknames. In addition, nicknames are frequently changed in the online community, so it is difficult to identify them. Therefore, in this paper, to remedy these problems we propose a behavior pattern feature vectors for users considering online community characteristics, propose a new implicit behavior pattern called relationship pattern, and identify the nickname of the same user based on Random Forest classifier. Also, Experimental results with the collected real world online community data demonstrate that the proposed behavior pattern and classifier can identify the same users at a meaningful level.

• Journal of Convergence for Information Technology
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• v.8 no.5
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• pp.69-75
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• 2018

The purpose of access control is to prevent computing resources from illegal behavior such as leakage, modification, and destruction by unauthorized users. As the cloud computing environment is expanded to resource sharing services using virtualization technology, a new security model and access control technique are required to provide dynamic and secure cloud-based computing services. The virtualization management convergence access control model provides a flexible user authorization function by applying the dynamic privilege assignment function to the role based access control mechanism. In addition, by applying access control mechanism based on security level and rules, we solve the conflict problem in virtual machine system and guarantee the safeness of physical resources. This model will help to build a secure and efficient cloud-based virtualization management system and will be expanded to a mechanism that reflects the multi-level characteristics.

• The KIPS Transactions:PartB
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• v.10B no.7
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• pp.795-802
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• 2003

To live autonomously, intelligent agents such as robots or virtual characters need ability that recognizes given environment, and learns and chooses adaptive actions. So, we propose an action selection/learning mechanism in intelligent agents. The proposed mechanism employs a hybrid system which integrates a behavior-based method using the reinforcement learning and a cognitive-based method using the symbolic learning. The characteristics of our mechanism are as follows. First, because it learns adaptive actions about environment using reinforcement learning, our agents have flexibility about environmental changes. Second, because it learns environmental factors for the agent's goals using inductive machine learning and association rules, the agent learns and selects appropriate actions faster in given surrounding and more efficiently in extended surroundings. Third, in implementing the intelligent agents, we considers only the recognized states which are found by a state detector rather than by all states. Because this method consider only necessary states, we can reduce the space of memory. And because it represents and processes new states dynamically, we can cope with the change of environment spontaneously.

• Journal of Korea Multimedia Society
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• v.7 no.7
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• pp.976-984
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• 2004

C# and .NET platform in Microsoft Corp. has been developed to meet the needs of programmers, and cope with Java and JVM platform of Sun Microsystems. After compiling, a program written in .NET language is converted to MSIL code, and also executed by .NET platform but not in JVM platform. Java, one of the most widely used programming languages recently, is the language invented by James Gosling at Sun Microsystems, which is the next generation language independent of operating systems and hardware platforms. Java source code is compiled into bytecode as intermediate code independent of each platform by compiler, and also executed by JVM. This paper presents the MSIL-to-Bytecode intermediate language translator which enables the execution of the program written in .NET language such as C or C# in JVM(Java Virtual Machine) environment, translating MSIL code produced by compiling .NET program into java bytecode. This work provides an environment for programmers to develop application programs without limitations of programming languages.

• Journal of Korea Multimedia Society
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• v.13 no.5
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• pp.754-762
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• 2010

Nowadays, email-based targeted attacks using malcode-bearing documents have been steadily increased. To improve the success rate of the attack and avoid anti-viruses, attackers mainly employ zero-day exploits and relevant social engineering techniques. In this paper, we propose an architecture of the email vaccine cloud system to prevent targeted attacks using malcode-bearing documents. The system extracts attached document files from email messages, performs behavior analysis as well as signature-based detection in the virtual machine environment, and completely removes malicious documents from the messages. In the process of behavior analysis, the documents are regarded as malicious ones in cases of creating executable files, launching new processes, accessing critical registry entries, connecting to the Internet. The email vaccine cloud system will help prevent various cyber terrors such as information leakages by preventing email based targeted attacks.

• Proceedings of the Korea Information Processing Society Conference
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• 2003.11b
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• pp.663-666
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• 2003

자바는 썬 마이크로시스템즈사의 제임스 고슬링(James Gosling)에 의해 고안된 언어로 운영체제 및 하드웨어 플랫폼에 독립적인 차세대 언어로 최근에 가장 널리 사용하는 범용 프로그래밍 언어 중 하나이다. 자바 프로그램은 컴파일러에 의해 각 플랫폼에 독립적인 중간 코드 형태의 바이트코드로 변환된 클래스 파일로 생성되면 JVM(Java Virtual Machine)에 의해 실행된다. 마이크로소프트사의 .NET 플랫폼과 C# 언어는 프로그래머들의 요구를 충족시키고 썬사의 JVM 환경과 자바 언어에 대응하기 위해서 개발된 플랫폼과 언어이다. C#과 같은 .NET 언어는 컴파일러에 의해 MSIL(MicroSoft Intermediate Language) 코드로 번역되며 번역된 MSIL 코드는 .NET 플랫폼 환경에서 런타임 엔진인 CLR(Common Language Runtime)에 의해 실행이 된다. 자바로 작성된 프로그램은 JVM 플랫폼에서는 실행이 되지만 .NET 플랫폼에서 실행이 되지 않고, 반대로 C#과 같은 .NET 언어로 작성된 프로그램은 .NET 플랫폼에서는 실행이 되지만 JVM 플랫폼에서 실행이 되지 않는다. 이런 이유로 본 논문에서는 자바소스를 컴파일하여 생성된 클래스 파일에서 Oolong 코드를 생성하고 생성된 Oolong 코드를 .NET의 MSIL 코드로 변환하여 자바로 구현된 프로그램이 .NET 환경에서 실행되도록 하는 Bytecode-to-MSIL 번역기 시스템을 구현하였다. 따라서, 자바 프로그래머는 JVM이나 .NET 플랫폼 환경에 관계없이 프로그램을 작성하여 실행시킬 수 있다. 번역기 시스템의 구현을 정형화하기 위해 Oolong 코드의 명령어들을 문법으로 작성하였으며, PGS를 통해 생성된 어휘 정보를 가지고 스캐너를 구성하였으며, 파싱테이블을 가지고 파서를 설계하였다. 파서의 출력으로 AST가 생성되면 번역기는 AST를 탐색하면서 의미적으로 동등한 MSIL 코드를 생성하도록 시스템을 컴파일러 기법을 이용하여 모듈별로 구성하였다.