• Journal of KIISE:Databases
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• v.31 no.4
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• pp.422-431
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• 2004

In recent years, different models in data delivery have been explored in mobile computing systems. Particularly, there were a lot of research efforts in the periodic push model where the server repetitively disseminates information without explicit request. However, average waiting time per data operation highly depends on the length of a broadcast cycle and different access pattern among clients may deteriorate the response time considerably. In this case, clients are preferably willing to send a data request to the server explicitly through backchannel in order to obtain optimal response time. We call the broadcast model supporting backchannel as hybrid broadcast. In this paper, we devise a new transaction processing algorithm(O-PreH) in hybrid broadcast environments. The data objects which the server maintains are divided into Push_Data for periodic broadcasting and Pull_Data for on-demand processing. Clients tune in broadcast channel or demand the data of interests according to the data type. Periodic invalidation reports from the server support maintaining transactional consistency. If one or more conflicts are found, conflict orders are determined not to violate the consistency(pre-reordering) and then the remaining operations have to be executed pessimistically. Through extensive simulations, we demonstrate the improved throughput of the proposed algorithm.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 1993.10a
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• pp.67-70
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• 1993

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.5B
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• pp.317-323
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• 2005

Broadcast disks are suited for disseminating information to a large number of clients in mobile computing environments. In broadcast disks, the server continuously and repeatedly broadcasts all data items in the database to clients without specific requests. The clients monitor the broadcast channel and retrieve data items as they arrive on the broadcast channel. The broadcast channel then becomes a disk from which clients can retrieve data items. This paper proposes a Timestamp based Concurrency Control (TCC) scheme to preserve the consistency of read-only client transactions, when the values of broadcast data items are updated at the server. Previous schemes tried to reduce transaction aborts by consuming considerable amount of downlink communication from the server to clients for transferring control information. On the other hand, the TCC uses a timestamp field of each data item to describe execution order of server transactions. Clients can allow more transaction executions by checking consistency of their read-only transactions with timestamps of data items. As a result, the TCC can reduce the abort ratio of client transactions with minimal control information to be broadcast from the server.

• Proceedings of the Korean Information Science Society Conference
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• 2002.04a
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• pp.565-567
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• 2002

인터넷과 무선 이동통신 등이 보편화되면서 두 기술을 접목한 WAP (Wireless Application Protocol)[1]이 등장하였으며, 다수의 사용자 요구를 동시에 효율적으로 처리하면서 다양한 무선 단말기로부터 요청을 신속하게 처리할 수 있는 WAP 게이트웨이(gateway)에 대한 연구가 여러 연구 그룹에서 수행되고 있다. 본 논문에서는 Java의 기본적인 서비스인 멀티쓰레드를 이용하고, 컨테이너 유효 리소스의 효율적 관리를 위해 접속 풀링(connection pooling) 기능과 우선순위 큐를 적용하여 WTP (Wireless Transaction Protocol)[2]를 구현한다. 우선순위에 입각하여 구현된 트랜잭션 서비스를 시뮬레이션을 통하여 성능을 분석한다.

• Proceedings of the Korea Information Processing Society Conference
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• 2000.10a
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• pp.59-62
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• 2000

최근 인터넷 사용자의 폭발적인 증가와 방대한 클라이언트를 갖는 이동 통신 응용 분야를 위해 방송 디스크 구조가 등장하였다. 당송 디스크 구조는 유선과 무선 두 환경을 모두 지원하며, 특히 데이타에 대한 경쟁이 심한 환경에 더욱 유용하다. 본 연구는 방송 디스크 환경의 클라이언트에서 실행되는 판독 전용 트랜잭션들을 위한 동시성 제어기법과 캐싱기법을 제안하고, 각 클라이언트가 액세스하는 데이타의 정확성을 보장할 수 있음을 보인다.

• Proceedings of the Korea Information Processing Society Conference
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• 2010.04a
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• pp.226-229
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• 2010

최근 프로세서가 코어 개수를 늘리는 구조로 발전함에 따라 병렬프로그래밍의 중요성이 더욱 강조되고 있다. 병렬프로그래밍에서 발생하는 공유자원에 대한 경쟁조건을 제어하기 위한 효율적인 방법으로 여러 가지 락-프리 동기화 기법이 제안되어 왔다. 그 중 소프트웨어 트랜잭션 메모리는 지금까지 하드웨어적인 방법과 소프트웨어적인 방법 등 여러 가지 방법으로 구현되었지만 여러 가지 하드웨어적인 제약과 기존의 소스코드를 수정해야 하는 문제점이 있다. 이러한 문제를 해결하기 위해 본 논문에서는 동적 코드 변환기술을 이용한 소프트웨어 트랜잭션 메모리 기법을 제안하고 기존 구현과 비교 평가하였다.

• Journal of KIISE:Databases
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• v.35 no.3
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• pp.257-271
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• 2008

Wireless broadcast environments has character that a number of mobile client can receive data streaming from central server no matter how they are so many. Because it is asymmetric bandwidth in that uplink and downlink bandwidth are different. This advantage helps wireless broadcast environments is used in many applications. These applications work almost read operation and need control concurrency using transaction unit. Previous concurrency control scheme in single channel is not adapted in multi channel environments because consistency of data are broken when a mobile client tunes in a broadcast cycle in a channel and then move into another channel and listen to different broadcast cycle with already accessed broadcast cycle. In this paper, we propose concurrency control for read-only mobile transactions in multiple wireless broadcast channel. First of all, we adapt index and data dedicated channel and propose LBCPC(Longest Broadcast Cycle Per Channel) as new unit of consistency. In index dedicated channel, it is repeatedly broadcasted data in same BCPC(Broadcast Cycle Per Channel) until LBCPC. And mobile transaction executes validation using control information every LBCPC. As a result, consistency of data is kept and average response time is shorter than one in single channel because waiting time for restart reduces. And as control information is broadcasted more frequently than in single channel, it is guaranteed currency about data accessed by transaction. Finally, according to the simulation result, we verify performance of our scheme in multi channel as comparing average response time with single channel.

• Journal of KIISE:Computing Practices and Letters
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• v.16 no.2
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• pp.247-251
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• 2010

Using SCM in storage systems introduce new potentials for improving I/O performance and reliability. In this paper, we study the use of SCM as a buffer cache that guarantees transactional unit writes. Our proposed method can improve storage system reliability and performance at the same time and can recover the storage system immediately upon a system crash. The Proposed method is based on the LINUX JBD(Journaling Block Device), thus reliability is equivalent to JBD. In our experiments, the file system that adopts our method shows better I/O performance even while guaranteeing high reliability and shows fast file system recovery time (about 0.2 seconds).

• The KIPS Transactions:PartD
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• v.10D no.2
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• pp.187-194
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• 2003

Main Memory storage system can increase the performance of the system by assigning enough slack time to real-time transactions. Due to its high response time of main memory devices, main memory resident data management systems have been used for location management of personal mobile clients to cope with urgent location related operations. In this paper we have developed a multi-threaded main memory storage system as a core component of real-time retrieval system to handle a huge amount of readers and writers of main memory resident data. The storage system is implemented as an embedded component which is working with the help of a disk resident database system. It uses multi-threaded executions and utilizes latches for its concurrency control rather than complex locking method. It only saves most recent data on main memory and data synchronization is done only when disk resident database asks for update transactions. The system controls the number of read threads and update threads to guarantee the minimum requirements of real-time retrievals.

• The Transactions of the Korea Information Processing Society
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• v.4 no.5
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• pp.1196-1210
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• 1997

Timestamp-Ordering Prltocol among trancaction scheduling alforithms can cause the priority teversion that a transaction with higher priority is processed after the teansaction the trancaction withe lower priority by assigning timestamp to transactions entering system and scheduling them based on the timestamp.To prevent this reversion,we suggest a data priority-based timestamp ordering prioity within the same timestamp group after grouping teansactions into constant time interval based on entering points.To evaluate the performance of this protocol,we compared the performance of this protocol with that of others after constructing the simulation environment with real time database system.We verified that the performance of proposed protocol is supweior to that of timestamp ordering protocol under the comdition of high load and high data conflicts.