• Journal of KIISE:Software and Applications
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• v.26 no.9
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• pp.1073-1084
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• 1999

이동 컴퓨팅 환경에서 이동 호스트는 제한된 대역폭을 효율적으로 사용하고 이동 트랜잭션의 응답 시간을 향상시키기 위하여 캐쉬를 이용한다. 그리고 이동 호스트에 캐슁된 데이타가 이동 지구국에서 갱신되면 이동 호스트의 캐쉬 일관성을 유지하기 위하여 이동 지구국은 무효화 메시지를 방송한다. 그러나 이동 지구국에서 주기적으로 무효화 메시지를 방송하는 방법은 이동 트랜잭션의 빠른 처리를 위하여 이동 지구국으로부터 데이타를 즉시 캐슁하는 경우에 이동 트랜잭션의 직렬가능한 수행을 보장할 수 없는 경우가 발생한다. 본 연구에서는 캐슁된 데이타를 이용하여 이동 트랜잭션을 수행하는 경우에 록을 이용하여 이동 트랜잭션의 직렬가능한 수행을 보장하는 UCL-MT 방법과 록 관리 방법을 제안한다. 제안하는 UCL-MT 방법은 이동 트랜잭션을 완료하기 이전에 이동 트랜잭션이 접근한 데이타 정보를 이용하여 지구국에서 사이클을 탐지함으로써 이동 트랜잭션의 직렬가능한 수행을 보장한다. 또한 제안하는 록 관리 방법은 이용할 수 있는 대역폭의 크기에 따른 무효화 메시지 내용의 변화에 유연하게 적용될 수 있다. Abstract In mobile computing environments, a mobile host caches the data to use the narrow bandwidth efficiently and improve the response time of a mobile transaction. If the cached data in mobile host is updated at a mobile support station, the mobile support station broadcasts an invalidation message for maintaining the cache consistency of a mobile host. But when a mobile transaction accesses the data which is not in cache, if a mobile host caches the data immediately from a mobile support station for processing a mobile transaction rapidly, the method that a mobile support station broadcasts an invalidation message periodically, happens to the case that can not guarantee the serializable execution of a mobile transaction. In this paper, we propose the UCL-MT method and lock management method, as a mobile transaction is executed using cached data. Since, using the data a mobile transaction accessed, the UCL-MT method detects a cycle in a mobile support station before the completion of the mobile transaction, it guarantees the serializable execution of the mobile transaction. Also, proposing lock management method can be adapted flexibly at the change of invalidation message content, according to the available bandwidth.

• The KIPS Transactions:PartD
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• v.9D no.2
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• pp.185-194
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• 2002

Most of mobile computing systems allow mostly read-only transactions from mobile clients for retrieving various types of Information such as stock data, traffic information and news updates. Since previous concurrence control protocols, however, do not consider such a particular characteristics, the performance degradation occurs when previous schemes are applied to the broadcast environment. In this paper, we propose OCC/UTF(Optimistic Concurrence Control with Update Transaction First) that is most appropriate for broadcast environment. OCC/UTF lets a query transaction, that has already read the data item which was invalidated by update transaction, read again the same data item without the abort of the query transaction due to non-serializability. Therefore, serializable order is maintained and the query transaction is committed safely regardless of commitment of update transactions. In OCC/UTF, Clients need not require server to commit their query transactions. Because of broadcasting the validation reports including values updated recently to clients, it reduces the overhead of requesting recent values from the server and the server need not also re-broadcast the newest values. As a result, OCC/UTF makes full use of the asymmetric bandwidth. It can also improve transaction throughput by increasing the commit ratio of query transactions as much as possible.

• 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.

• The Transactions of the Korea Information Processing Society
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• v.6 no.12
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• pp.3447-3455
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• 1999

Database correctness is guaranteed by standard transaction scheduling schemes like two-phase locking for the context of concurrent execution environment in which short-lived ones are normally mixed with long-lived ones. Traditional syntax-oriented serializability notions are considered to be not enough to handle in particular various types of transaction in terms of duration of execution. To deal with this situation, altruistic locking has attempted to reduce delay effect associated with lock release moment by use of the idea of donation. An improved form of altruism has also been deployed in extended altruistic locking in a way that scope of data to be early released is enlarged to include even data initially not intended to be donated. In this paper, we first of all investigated limitations inherent in both altruistic schemes from the perspective of alleviating starvation occasions for transactions in particular of short-lived nature. The idea of two-way donation locking(2DL) has then been experimented to see the effect of more than single donation in distributed database systems. Simulation experiments shows that 2DL outperforms the conventional two-phase locking in terms of the degree of concurrency and average transaction waiting time under the circumstances that the size of long-transaction is in between 5 and 9.