• The KIPS Transactions:PartD
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• v.8D no.5
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• pp.543-552
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• 2001

To process transactions in fully replicated database, an atomic broadcast is mainly used. In this case of using atomic broadcast, transactions can be delayed because of the coordinating step among servers before processing the transaction. In this paper, we propose an algorithm to resolve the problem of transaction delay. In the proposed algorithm, the transactions are processed by using the optimistic method. The operations of a transaction are performed in the site that it is submitted and its write operations its updates atomically in all replicated sites. Since the serializability of transaction is ensured by checking the sequence number of transactions in the completion-inspection step.

• Proceedings of the Korea Information Processing Society Conference
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• 2002.04a
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• pp.341-344
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• 2002

기존에 제안된 대부분의 중복 기법은 원본 트랜잭션을 완료한 후 비동기로 중복 사본에 대한 갱신 요구를 방송하는 지연 갱신 기법을 가정하였다. 지연 갱신 기법은 즉시 갱신 기법에서 발생하는 빈번한 교착상태 발생 문제를 해결할 수는 있지만 데이타 일관성 유지가 사용자 책임이라는 단점을 갖는다. 최근 그룹통신을 이용한 즉시 갱신 중복 기법들이 제안되고 있다. 이들 기법은 메시징 순서를 이용하여 교착상태 발생률을 줄였지만, 송신 노드는 갱신 요구 메시지를 방송한 후 전역 직렬성을 검증하는 낙관적 기법을 채택하기 때문에 통시성이 증가할수록 철회 트랜잭션의 실행 오버헤드가 증가한 다는 문제점을 갖는다. 본 논문에서는 철회 트랜잭션의 갱신 메시지 방송과 실행 오버헤드를 줄일 수 있는 즉시 갱신 기법을 제안한다. 제안한 기법은 갱신 요구 메시지를 방송하기 전에 전역 직렬성 검사가 이루어지기 때문에 완료 트랜잭션은 한번의 메시지 방송으로 처리할 수 있다. 뿐만 아니라, 철회 트랜잭션은 다른 노드로 방송할 필요가 없기 때문에 메시지 전송 횟수를 줄일 수 있으며, 철회 트랜잭션의 실행으로 인한 디스크 액세스 수와 로크 대기 시간을 줄임으로써 성능을 향상시킨다.

• Journal of KIISE:Databases
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• v.29 no.6
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• pp.502-512
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• 2002

Most of previous replication schemes assume lazy schemes, which asynchronously propagate replica updates to other nodes after the updating transaction commits. While lazy schemes are novel in the sense that they can resolve high deadlock frequencies of eager schemes, they suffer from the fact that users should be responsible for the data consistency. Recently replication schemes based on the messaging order of group communication have been studied. They can reduce the deadlock frequencies using the messaging order, but they have another problem of increasing execution overhead of aborted transactions at high degree of concurrency. This is because the sender node validates global serializability after multicasting replica update messages to other nodes. In this paper, we propose an efficient eager replication scheme for reducing the number of messaging and overhead of aborted transactions significantly. The proposed scheme validates any conflicts before multicasting and does not multicast when there is any conflict; hence, it can exploit performance improvement by alleviating the message traffic for replica update or by reducing the number of disk accesses and locking delay due to aborted transactions.

• Journal of KIISE:Databases
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• v.29 no.6
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• pp.500-500
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• 2002

Most of previous replication schemes assume lazy schemes, which asynchronously propagate replica updates to other nodes after the updating transaction commits. While lazy schemes are novel in the sense that they can resolve high deadlock frequencies of eager schemes, they suffer from the fact that users should be responsible for the data consistency. Recently replication schemes based on the messaging order of group communication have been studied. They can reduce the deadlock frequencies using the messaging order, but they have another problem of increasing execution overhead of aborted transactions at high degree of concurrency. This is because the sender node validates global serializability after multicasting replica update messages to other nodes. In this paper, we propose an efficient eager replication scheme for reducing the number of messaging and overhead of aborted transactions significantly. The proposed scheme validates any conflicts before multicasting and does not multicast when there is any conflict; hence, it can exploit performance improvement by alleviating the message traffic for replica update or by reducing the number of disk accesses and locking delay due to aborted transactions.

• The KIPS Transactions:PartA
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• v.11A no.6
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• pp.459-468
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• 2004

Sharing XML trees on mobile devices has become more and more popular. Optimistic replication of XML trees for mobile devices raises the need for reconciliation of concurrently modified data. Especially for reconciling the modified tree structures, we have to compare trees by node mapping which takes O($n^2$) time. Also, using semantic based conflict resolving policy is often discussed in the literature. In this research, we focused on an efficient reconciliation method for mobile environments, using edit scripts of XML data sent from each device. To get a simple model for mobile devices, we use the XML list data sharing model, which allows inserting/deleting subtrees only for the repetitive parts of the tree, based on the document type. Also, we use keys for repetitive part subtrees, keys are unique between nodes with a same parent. This model not only guarantees that the edit action always results a valid tree but also allows a linear time reconciliation algorithm due to key based list reconciliation. The algorithm proposed in this paper takes linear time to the length of edit scripts, if we can assume that there is no insertion key conflict. Since the previous methods take a linear time to the size of the tree, the proposed method is expected to provide a more efficient reconciliation model in the mobile environment.

• Journal of KIISE:Databases
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• v.28 no.3
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• pp.512-527
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• 2001

In a client-server spatial database, it is desirable to maintain the cached data in a client side to minimize the communication overhead across a network. This paper deals with the issues of concurrency and consistency of map updates in this environment. A client transaction to update map data is an interactive work and takes a long time to complete it. The map update in a client site may affect the other sites'updates because of dependencies between spatial data stored at different sites. The concurrent updates should be propagated to the other clients as well as the server to keep the consistency of map replicated in a client cache, and also the communication overhead of the update propagation should be minimized not to lose the benefit of caching. The newly proposed cache region locking with CR lock and CX lock controls the update dependency due to spatial relationships. CS lock and COD lock are suggested to use optimistic detection-based approaches for guaranteeing the consistency of cached client data. The cooperative update protocol uses these extended locking primitives and Spatial Relationship-based 2PC (SR-based 2PC). This paper argues that the concurrent updates of cached client spatial data can be achieved by deciding on collaborative updates or independent updates based on spatial relationships.