• Proceedings of the Korean Information Science Society Conference
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• 2005.11b
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• pp.37-39
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• 2005

브로드캐스트는 하나 또는 여러 개의 채널을 이용해서 다수의 모바일 클라이언트들이 빈번하게 필요로 하는 데이터를 효과적으로 전송하기 위한 방법 중의 하나이다. 무선 브로드 캐스트 환경에서는 모바일 클라이언트의 제한된 자원과 모바일 클라이언트에서 서버로의 제한된 상향 대역폭 등의 이유로 기존의 동시성 제어 기법을 그대로 사용할 수 없다. 이러한 이유로 무선 브로드캐스팅 환경을 위한 동시성 제어 기법들이 많이 연구 되어 왔다. 하지만 지금까지 제안된 동시성 제어기법들은 단일 채널 환경 하에 하나의 브로드캐스트 주기 동안 브로드캐스팅 되는 데이터 간에는 일관성을 가진다는 가정 하에 동시성 제어 기법들이 진행되어 왔다. 그러나 다중 채널 환경에서는 여러 가지 이유로 단일채널의 동시성 제어 기법을 적용할 수 없다. 본 논문에서는 다중채널 브로드캐스팅 환경에서 읽기 전용 트랜잭션을 처리하기 위한 동시성 제어 기법을 제안하였다.

• Proceedings of the IEEK Conference
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• 2000.07b
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• pp.735-738
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• 2000

The most important issue in database security is correct concurrency control under the restrictive security policy. The goal of secure transaction management is to keep security and provide many concurrent users with the high availability of database. In this paper, we consider the security environment of multidatabase system with replicated data. The read-from relationship in the existed serializability is improper in security environment. So, we define new read-from relationship and propose new secure 1-copy quasi-seriailzability by utilizing this relationship and display some examples. This security environment requires both the existed local autonomy and the security autonomy as newly defined restriction. To solve covert channel problem is the most difficult issue in developing secure scheduling scheme. The proposed secure 1-copy quasi-serializability is very proper for global transactions in that this serializability not violates security autonomy and prevents covert channel between global transactions.

• Proceedings of the Korea Information Processing Society Conference
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• 2000.04a
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• pp.61-66
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• 2000

본 논문에서는 분산 실시간 데이터베이스 시스템을 위한 효율적인 동시성 제어 기법을 제안한다. 제안하는 기법은 분산 실시간 환경에서 완료준비 단계에 도달한 트랜잭션의 우선 순위를 상승시킴으로써 트랜잭션의 재시작에 의한 낭비를 줄이고, 트랜잭션의 완료를 최대한 보장하며, 잠금 지연 시간을 최소화하는 장점을 갖는다. 또한, 제안하는 기법은 우선 순위가 상승된 트랜잭션의 완료를 보장하며 데이터 차용(borrowing)을 통해 다른 트랜잭션의 지연시간을 줄여줌으로써 전체적인 시스템 성능을 향상시킨다.

• Journal of KIISE:Databases
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• v.28 no.3
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• pp.458-467
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• 2001

Optimistic Two-Phase Locking(O2PL) performs as well as or better than the other approaches because it exploits client caching well and also has relatively lower network bandwidth requirements. However, O2PL leads to unnecessary waits, because, it can not be commit a transaction until the transaction obtains all requested locks. In addition, Optimistic Concurrency Control(OCC) tends to make needless aborts. This paper suggests an efficient optimistic cache consistency protocol that overcomes such shortcomings. Our scheme decides whether to commit or abort a transaction without wait and it adopts transaction re-ordering in order to minimize the abort rate. Our scheme needs only one version for each data item in spite of the re-ordering mechanism used. Finally, this paper presents a simulation-based analysis that shows superiority in performance of out scheme to O2PL and OCC.

• Convergence Security Journal
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• v.20 no.3
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• pp.71-78
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• 2020

Bitcoin-based blockchain technology provides an infrastructure that enables anonymous smart contracts, low-cost remittances, and online payments. However, the block-chain technology that implements the bitcoin has scalability constraints in tradeoffs between throughput and latency. To solve these problems, the Byzantine fault tolerant block-chain technique has been proposed. This technique improves throughput without increasing latency by selecting a leader and constructing many microblocks that do not contain proofs of work within the existing block by the leader. However, this technique may be less secure than existing techniques in selecting the reader.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.20 no.5
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• pp.107-112
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• 2020

Recently, unstructured data is rapidly being produced based on web-based services. NoSQL systems and key value stores that process unstructured data as key and value pairs are widely used in various applications. In this paper, a study was conducted on a skip list used for in-memory data management in an LSM-tree based key value store. The skip list used in the key value store is an insertion-based skip list that does not allow overwriting and processes all changes only by inserting. This behavior can support Multi-Version Concurrency Control (MVCC), which can simultaneously process multiple read/write requests through snapshot isolation. However, since duplicate keys exist in the skip list, the performance significantly degrades due to unnecessary node visits during a list traverse. In particular, serious overhead occurs when a range query or scan operation that collectively searches a specific range of data occurs. This paper proposes a newly designed Stride SkipList to reduce this overhead. The stride skip list additionally maintains an indexing pointer for the last node of the same key to avoid unnecessary node visits. The proposed scheme is implemented using RocksDB's in-memory component, and the performance evaluation shows that the performance of SCAN operation improves by up to 350 times compared to the existing skip list for various workloads.

• The Transactions of the Korea Information Processing Society
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• v.7 no.8
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• pp.2310-2326
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• 2000

Client-server DBMS based on a data-shipping model can exploit e1ient resources effectively by allowing inter-transaction caching. However, inter-transaction caching raises the need of transactional cache consistency maintenancetTCCM protocol. since each client is able to cache a portion of the database dynamically. Deferred locking(DL) is a new detection-based TCCM scheme designed on the basis of a primary copy locking algorithm. In DL, a number of lock ,ujuests and a data shipping request are combined into a single message packet to minimize the communication overhead required for consistency checking. Lsing a simulation model. the performance of the prolxlsed scheme is compared with those of two representative detection based schemes, the adaptive optimistic concurrency control and the caching two-phase locking. The performance results indicate that DL improves the overall system throughput with a reasonable transaction abort ratio over other detection - based schemes.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2017.10a
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• pp.569-570
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• 2017

Bitcoin-based blockchain technology provides an infrastructure that enables anonymous smart contracts, low-cost remittances, and online payments. However, the block-chain technology that implements the bitcoin has scalability constraints in tradeoffs between throughput and latency. To solve these problems, the Byzantine fault tolerant block-chain technique has been proposed. This technique improves throughput without increasing latency by selecting a leader and constructing many microblocks that do not contain proofs of work within the existing block by the leader. However, this technique may be less secure than existing techniques in selecting the reader. In this paper, we propose a technique for scalability of the blockchain technology by using microblock technology and parallel execution technique. Within one microblock there is information about several transactions. In the proposed scheme, the throughput of the microblocks can be increased by performing concurrently.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.9
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• pp.2422-2432
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• 1996

In this thesis, we analyze the Broadcast and Select Network(BSN) architecture coming up to the issues among those in the single-hip WDM networks and the degradation of performance in consequence of the traffic imbalance which well be able to be produced in these network. We propose WDM networks architecture which can support concurrency services by using Array Wavelength Tunable Filter(AWTF) with the parrallel hardware structure as a solution. For the sake of multichannel communications, we make use of the Single Control channel, Multiple Data channel(SCMD) scheme that is one of the channel architecture. Also, we compare and analize the throughput of Uniform & Nonuniform traffic conditions, and obtain the optimized number of AWTF being able to guarantee the Quality of Service(QoS) required by the enlargement of WDM netowrks and traffic imbalance. Therefore, we can make it possible that the design of the WDM networks with BSN architecture ensures the optimized performance.

• The KIPS Transactions:PartD
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• v.9D no.2
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• pp.235-242
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• 2002

We propose an advanced transaction scheduling protocol for concurrency control of multilevel secure databases in wireless mobile network environment. Wireless communication is characterized by frequent spurious disconnections. So short-lived transaction must quickly access database without any delay by long-lived one. We adapted two-phase locking protocol, namely traditional syntax-oriented serializability notions, to multilevel secure databases in wireless mobile network environment. Altruistic locking, as an advanced protocol, has attempted to reduce delay effect associated with lock release moment by use of the idea of donation. An improved form of a1truism has also been deployed for extended a1truistic locking. This is in a way that scope of data to he early released is enlarged to include even data initially not intended to be donated. Our protocol is based on extended altruistic locking, but a new method, namely bi-directional donation locking for multilevel secure databases (MLBiDL), is additionally used in order to satisfy security requirements and concurrency. We showed the Simulation experiments that MLBiDL outperforms the other locking protocols in terms of the degree of throughput and average waiting time.