• Proceedings of the Korean Information Science Society Conference
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• 2008.06a
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• pp.303-304
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• 2008

• The Transactions of the Korea Information Processing Society
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• v.7 no.7
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• pp.2219-2228
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• 2000

Caches in a multiprocessing environment introduce the cache coherence problem. When multiple processors maintain locally cached copies of a unique shared-memory location, any local modification of the location can result in a globally inconsistent view of memory. Cache coherence protocols are important to operate a shared-memory multiprocessor system with efficiency and correctness. Since random testing and simulations are not enough to validate correctness of protocols, it is necessary to develop efficient and reliable verification methods. In this appear we present our experience in using VIS (Verification Interacting with Synthesis), a tool of formal method, to analyze a number of property of a cache coherence protocol, RACE (Remote Access Cache coherent Enforcement).

• Journal of KIISE:Databases
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• v.37 no.3
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• pp.171-175
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• 2010

This paper analyzes the tag data inconsistency problem caused by incomplete execution of the tag access operation to the RFID tag's memory and proposes a protocol to control consistent tag data accesses with finalizing the incomplete operation. Passive RFID tag cannot guarantee complete execution of the tag access operations because of uncertainty and unexpected disconnection of RF communications. This leads to the tag data inconsistency problem. To handle this, we propose a concurrency control protocol which defines incomplete tag operations as continuous queries and monitors the tags're-observation continuously. The protocol finalizes the incomplete operation when the tag is re-observed while it blocks inconsistent data accesses from other operations. We justify the proposed protocol by analyzing the completeness and consistency. The experiments show that the protocol shows better performance than the traditional lock-based concurrency control protocol.

• 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:Computer Systems and Theory
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• v.32 no.7
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• pp.349-358
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• 2005

False sharing is a result of co-location of unrelated data in the same unit of memory coherency, and is one source of unnecessary overhead being of no help to keep the memory coherency in multiprocessor systems. Moreover. the damage caused by false sharing becomes large in proportion to the granularity of memory coherency. To reduce false sharing in a page-based DSM system, it is necessary to allocate unrelated data objects that have different access patterns into the separate shared pages. In this paper we propose call-site tracing-based shared memory allocator. shortly CSTallocator. CSTallocator expects that the data objects requested from the different call-sites may have different access patterns in the future. So CSTailocator places each data object requested from the different call-sites into the separate shared pages, and consequently data objects that have the same call-site are likely to get together into the same shared pages. We use execution-driven simulation of real parallel applications to evaluate the effectiveness of our CSTallocator. Our observations show that by using CSTallocator a considerable amount of false sharing misses can be additionally reduced in comparison with the existing techniques.

• The KIPS Transactions:PartD
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• v.12D no.1 s.97
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• pp.21-30
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• 2005

In mobile computing environments, a mobile host caches the data to use the narrow bandwidth efficiently and improve the response time. A server periodically broadcasts the update data for maintaining the cache consistency of a mobile host. However, a method for maintaining cache consistency using periodic invalidation report has a problem that defers the commit decision of a mobile transaction to guarantee its serializable execution. In this paper, we propose CCM-AD method that guarantees the serializable execution of a mobile transaction even in the case that it is executed using cached data. As CCM-AD method guarantees the serializable execution of mobile transactions by using the intersection between the data broadcast to mobile host and the data updated at server. Then the CCM-AD method can reduce the delay of commitment decision of a mobile transaction. Also our method can reduce the size of invalidation report.

• Proceedings of the Korean Information Science Society Conference
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• 2004.10b
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• pp.202-204
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• 2004

최근 이동컴퓨팅(Mobile Computing) 환경에서의 잦은 접속 단절로 인한 클라이언트 캐시 일관성(consistency) 문제를 해결하기 위한 방법과 함께 통신 대역과 에너지의 제약을 고려한 연구가 진행되고 있다. 이러한 캐시 유지 방법의 한 분야로서 방송(Broadcasting)에 대한 연구가 진행 중이다. 그러나 기존의 무효화 보고에 대한 연구는 서버에서의 갱신 정도와 상관없이 전송되기 이전 일정 시간동안의 서버갱신에 대한 정보만을 포함한다. 이러한 전송기법은 다수의 클라이언트가 필요로 하면서 갱신정도가 빈번한 데이터에는 적합한 방송 방법이 아니다. 본 논문은 이 같은 단정을 보안하기 위해 자주 갱신되는 데이터의 빈도 수에 따라 데이터를 방송하고 클라이언트의 요청에 의해서 데이터 방송빈도 수를 변경하여 클라이언트가 특정 데이터의 응답시간을 최소화 할 수 있도록 하는 방안을 제시하였다.

• Proceedings of the Korea Society for Simulation Conference
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• 1999.10a
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• pp.133-137
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• 1999

STAREX 교환기의 DBMS는 교환기 시스템의 호처리, 운용, 보전 등에 관련된 모든 데이터를 유지하면서, 응용 프로그램 데이터의 효율적 지원, 데이터의 일관성 유지, 데이터의 백업, 데이터의 무결성 진단 및 복구 등의 종합적인 관리를 수행하는 시스템 소프트웨어이다. 또한, DBMS는 교환기의 실시간 처리 요구를 만족시키기 위하여 여러 가지 기능들을 제공한다. 그러나, 이러한 기능들은 응용 프로그램들이 얼마나 효율적으로 사용 하느냐에 따라 성능이 크게 좌우된다. 본 논문에서는 STAREX 교환기의 DBMS가 제공하는 실시간 처리 기능들을 소개하고, 교환기의 성능을 향상시키기 위하여 응용 프로그램들이 효율적으로 데이터베이스에 접근하는 방안을 제시한다.

• The Journal of Information Technology
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• v.3 no.3
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• pp.117-134
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• 2000

Client-server DBMS based on a data-skipping model can exploit client resources effectively by allowing inter-transaction caching. However, inter-transaction caching raises the need of transactional cache consistency maintenance(TCCM) protocol, since each client is able to cache a portion of the database dynamically. Detection-based TCCM schemes can reduce the message overhead required for cache consistency if they validate clients replica asynchronously, and thus they cm show high throughput rates. However, they tend to show high ratios of transaction abort since transactions can access invalid replica. For coping with this drawback, this paper develops a new notion of shadow transaction, which is a backup-purpose one that is kept ready to replace an aborted transaction. This paper proposes a new detection-based TCCM scheme named DL-ST on the basis of the notion of shadow transaction. Using a simulation model, this paper evaluates the effect of shadow transaction in terms of transaction through rate and abort ratio.

• Journal of KIISE:Databases
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• v.32 no.3
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• pp.276-284
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• 2005

In the mobile computing environment, caching data at the client's side is a useful technique for improving the performance. For caching to be effective, the cache contents must be consistent with those stored in the server. That is, unfortunately, difficult to enforce due to the frequent disconnection and mobility of clients. In the literature, the basic approach adopted is for the sever to periodically broadcast invalidation reports(IRs) that contain information about objects that have been updated recently. However IR-based cache maintenance scheme has a main drawback. Any client who has been disconnected longer than w seconds has to discard all cached items even some of them may still be valid. In this paper, we propose two main schemes which can adapt clients' losing IR messages by long disconnection. First, the client sends its disconnection time when connection is re-established, and the server uses this information to decide the size of broadcast window w dynamically. Second, the server maintains IR messages for a given period of time and a client who has been disconnected longer than w seconds can verify its cache consistency individually. Compared to previous IR-based schemes, our schemes can significantly reduce cache missing and uplink request and improve the throughput by reducing response time.