• 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.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.8
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• pp.1834-1839
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• 2005

Database security is essential to protect their data in most organization such as hospitals, central or local governments, banks which manage the private, sensitive and important data. Because the duty of the department recently became more various and complicated, the changes of security requirement are needed more frequently. Therefore, easily changeable, flexible security policy and efficient security management with preserving the integrity of security policy are very important. In this paper, we implemented a flexible database security system in the specimen and clinical information management system of leukemic research center using IRH(Improved Role Hierarchy). Data is protected by MAC and we propose a flexible access control and effective administration by using the IRH that is an improved role hierarchy of RBAC. If security policy is needed for changes, this system can do it easily by simply modifying the IRH with the decentralized administration. The modified security policy can be applied flexibly after alteration because the security level of the subject is not fixed but can be derived automatically from the IRH when user connects the system.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.9 no.3
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• pp.298-305
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• 2016

Various NoSQL databases are more excellent to process a large amount of big data than existing relational databases such as MySQL, PostgreSQL and Oracle. Among widely used NoSQL databases, performance of HBase, Cassandra, MongoDB and Redis was comparatively assessed. For distributed processing of a large amount of data, 12 servers were connected through switching hub and Ubuntu was installed as operating system. As for benchmark tool, YCSB was applied. Read and update ratios changed from 50% and 50%, 95% and 5% and finally, 100% and 0% and each of them was assessed as 200,000 commands developed into 1,200,000 commands for each case. Cassandra was most excellent with transaction processing per second while MongoDB was most excellent with the number of processes carried out per unit time.

• Journal of the Korean Society for Railway
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• v.19 no.4
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• pp.445-455
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• 2016

A goal of the Real-time railway safety supervision system is to improve the safety oversight efficiency and to prevent accidents by integrating existing distributed monitoring systems, train, signal, power and facilities. So, the system require better performance regarding real-time processing based on big data. The disk-based database that is used in existing railway control systems has a problem with real-time processing; memory-based databases haves a limitation in terms of big-data processing; and time series databases haves a limitation in terms of real-time processing. So, we need a new database architecture for simultaneous real-time processing based on big data. In this study, we review the existing railway monitoring systems and propose a new database architecture for a real-time railway safety supervision system.

• The Transactions of the Korea Information Processing Society
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• v.7 no.9
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• pp.2797-2806
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• 2000

Recently, DDSs(Distributed Database Systems) have been implemented on V AN(V alue Added Network) as we know the amazing expansion of information network. DDS can yield significant cost and response time advantages over centralized systems for geographically distributed organizations. However, inappropriate design can result in high cost and poor response time to maintain the database at each site. In a DDS design, the main problem is how to select proper computer and how to allocate data fragment into a proper site. In this paper, we address DDS design problem of selecting the proper class of computers and the allocating data files on VAN. Also, the formulated model includes two objectives, the waited response time and the investment cost to include their relationship. Specially, the formulation of waited response time is based on M/M/1 queueing system to evaluate more precisely. GA(Genetic Algorithm), a kind of heuristic search method, is developed to search an optimal solution in the proposed design model and we show the simulation result to examine the algorithm performance.

• Journal of the Korean Society for information Management
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• v.15 no.3
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• pp.151-173
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• 1998

National Union Catalog presupposes an information infrastructure which permits users to identify and locate materials of all the domestic libraries and to share materials among libraries. Recently, there have been developed national union catalog projects in many countries using Z39.50 protocol implementation. In Korea, multi-union catalogs based on the types of libraries, i.e., public, academic, and special libraries, have been constructed separately. The virtual national union catalog which is a decentralized electronically accessible catalog unified by linking the databases of several institutions using Z39.50 is preferable to a union catalog implemented by a single centralized database. In this paper, hybrid union catalog is suggested with mixtures of centralized union catalogs and Z39.50-based distributed search systems for the development of a national union catalog. It is also suggested that the roles of a national library and centers for union catalog, and relationships between two types of institution for making sound ground for implementing the virtual Korean union catalog.

• The Journal of the Korea Contents Association
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• v.16 no.6
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• pp.441-449
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• 2016

The integrated data is an essential in the analysis for the balanced development of the local governments, but economic, social and cultural data in local governments is not being made with integrated management. A variety of information is being published according to the Government 3.0 era, but the researchers has great difficulty in integrating the analysis for one topic because related information is scattered in various sites. This paper proposes an integrated database(DB) of local governments to support the research activities. It has to contains total information of economic, social and cultural activities of local governments, and accommodate the distributed and heterogeneous data. It has the schema designed to integrate the entire data for considering the differences between local governments or data components. We should focus to build a framework for the multifaceted research to enable the cross analysis over common elements.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.11
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• pp.2067-2075
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• 2017

Lately big data processing is considered as an emerging issue. As a huge amount of data is generated, data processing capability is getting important. In processing big data, both Hadoop distributed file system and unstructured date processing-based NoSQL data store are getting a lot of attention. However, there still exists problems and inconvenience to use NoSQL. In case of low volume data, MapReduce of NoSQL normally consumes unnecessary processing time and requires relatively much more data retrieval time than RDBMS. In order to address the NoSQL problem, in this paper, an interworking scheme between NoSQL and the conventional RDBMS is proposed. The developed auto-mapping scheme enables to choose an appropriate database (NoSQL or RDBMS) depending on the amount of data, which results in fast search time. The experimental results for a specific data set shows that the database interworking scheme reduces data searching time by 35% at the maximum.

• KIPS Transactions on Software and Data Engineering
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• v.4 no.2
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• pp.77-82
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• 2015

Big Data technology has been attracted much attention in aspect of fast data processing. Research of practicing Big Data technology is also ongoing to process large-scale structured data much faster in Relatioinal Database(RDB). Although there are lots of studies about measuring analyzing performance, studies about structured data loading performance, prior step of analyzing, is very rare. Thus, in this study, structured data in RDB is tested the performance that loads distributed processing platform Hadoop using Apache sqoop. Also in order to analyze the influence factors of data loading, it is tested repeatedly with different options of data loading and compared with data loading performance among RDB based servers. Although data loading performance of Apache Sqoop in test environment was low, but in large-scale Hadoop cluster environment we can expect much better performance because of getting more hardware resources. It is expected to be based on study improving data loading performance and whole steps of performance analyzing structured data in Hadoop Platform.

• The KIPS Transactions:PartD
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• v.12D no.4 s.100
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• pp.531-542
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• 2005

In this paper, we propose the MDBMS(Multi-DataBase Management System) which integrates the LDBMSs(Local DataBase Systems) with heterogeneous environment into distributed system and provides global users with rapidly query process. For designing the MDBMS, we define the functions of components and design the interaction among them. In a point of view of the global view manager in components, we describe the following 3 cases; (1)the case which the results for the global query are all stored to the global view repository, (2)the case which no result exists in the global view repository, and (3)the case which the partial results we stored to the global view repository. By comparing above cases, we establish the functionalities of our MDBMS through the sequence diagram including the interlace of among objects and the method calling. Finally, we propose the model designed in the concrete by showing the executing procedures of each function using sample query on established functions mentioned above.