• Journal of KIISE:Computer Systems and Theory
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• v.33 no.5
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• pp.282-296
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• 2006

In a wireless client server environment, data broadcasting is an efficient data dissemination method; a server broadcasts data, and some of broadcasted data are cached in a mobile client's cache to save the narrow communication bandwidth, limited resources, and data access time. A server also broadcasts invalidation reports to maintain the consistency between server data and a client's cached data. Most of existing works on the cache consistency problems simply purge the entire cache when the disconnection time is long enough to miss the certain amount(window size) of IRs. This paper presents a cache invalidation method to increase mobile clients' cache reusability in case of a long disconnection. Instead of simply dropping the entire cache regardless of its consistency, a client estimates the cost of purging all the data with the cost of selective purge. If the cost of dropping entire cache is higher, a client maintains the cache and selectively purge inconsistent data using uplink bandwidth for validation request. The simulation results show that this scheme increases the cache reusability since it effectively considers the update rates and the broadcast frequencies of cached data in estimating the cost of cache maintenance.

• Proceedings of the IEEK Conference
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• 2003.07d
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• pp.1327-1330
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• 2003

The internet SCSI(iSCSI) disk has been studied as a storage system which can be directly connected to TCP/IP network. We designed and implemented a shared disk following the iSCSI protocol and providing cache consistency. It is named as intelligent iSCSI(i$^2$SCSI) disk. The i$^2$SCSI disk provides cache consistency of all blocks that belong to the disk using a conventional lease method and it uses 'contiguous blocks-level locking' The prototype of the i$^2$SCSI disk emulator and its client is designed and implemented in Linux 2.4.

• The KIPS Transactions:PartD
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• v.10D no.4
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• pp.655-660
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• 2003

The cache used by mobile host is an important device that recovers the weak points of limited power and bandwidth, in mobile computing environments. However, it has to stand and maintain the consistency with the server data. In this paper, we propose a 'Selective Cache Consistency Scheme'. The server allows an effective broadcasting by selecting data of high usability using 'Cache State Table' and 'Data Access Table'. Moreover, this scheme prevents the loss of data that nay occur by a long period of disconnection, by asynchronous broadcasting and transmitting those broadcast data preserved in the server. This also allows user to possess the latest data. Through experiments, we have found that the enlargement of autonomy is possible by reducing the dependence of server.

• Journal of KIISE:Computer Systems and Theory
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• v.30 no.7_8
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• pp.426-433
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• 2003

Management policies of Web Proxy Cache, for the QoS of Web users, are mainly focused on the page replacement and the data consistency policy. But the two subjects have been studied independently to each other regardless of its possibility of cooperation. In this paper, we introduce the performance improvement obtained by adapting the characteristic of LMF used in data consistency policy to LRU, thus taking the better performance synergy as a result of complementary cooperation. Various policies for the management of Web Proxy Cache are in progress, this study can be a way of performance guide to increase cache hit ratio and reduce the transmission overhead of Web Server.

• 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.

• The KIPS Transactions:PartD
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• v.8D no.5
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• pp.593-604
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• 2001

A database sharing system (DSS) refers to a system for high performance transaction processing. In the DSS, the processing nodes are coupled via a high speed network and share a common database at the disk level. Each node has a local memory and a separate copy of operating system. To reduce the number of disk accesses, the node caches data pages and index pages in its memory buffer. In general, B-tree index pages are accessed more often and thus cached at more processing nodes, than their corresponding data pages. There are also complicated operations in the B-tree such as Fetch, Fetch Next, Insertion and Deletion. Therefore, an efficient cache consistency scheme supporting high level concurrency is required. In this paper, we propose cache consistency schemes using identifiers of index pages and page_LSN of leaf page. The propose schemes can improve the system throughput by reducing the required message traffic between nodes and index re-traversal.

• The KIPS Transactions:PartD
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• v.13D no.1 s.104
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• pp.11-22
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• 2006

As we are to deal with more and more XML documents, research on storing and managing XML documents in databases are actively conducted. Employing RDBMS or ORDBMS as a repository of XML documents is currently regarded as most practical. The query results out of XML documents stored in databases could be cached for query performance though the cost of cache consistency against the update of the underlying data is incurred. In this paper, we assume that an ORDBMS is used as a repository for the XML query cache as well as its underlying XML documents, and that XML query cache is refreshed in a deferred way with the update log. When the same XML document was updated multiple times, the deferred refresh of the XML query cache may Bet inefficient. We propose an algorithm that removes or filters such duplicate updates. Based on that, the optimal SQL statements that are to be executed for XML query cache consistency are generated. Through experiments, we show the efficiency of our proposed deferred refresh of XML query cache.

• Journal of Advanced Navigation Technology
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• v.10 no.2
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• pp.120-127
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• 2006

Data-caching of a client is an important technology for interaction with a server where data are cached and operated at the client node. Caching reduces network latency and increases resource utilization at the client. In a Client-server environment, the absence of cache consistency algorithm, we cannot guarantee the correctness of client applications. In this paper, we propose a new asynchronous avoidance-based cache consistency algorithm. We remove the additional callback due to the lock escalation in AACC. With a comprehensive performance analysis, we show that the proposed algorithm has less message exchange than the AACC. One-copy serializability is used for proving correctness of the proposed algorithm.

• Journal of the Korea Society of Computer and Information
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• v.17 no.5
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• pp.41-48
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• 2012

A Vehicular Ad-hoc Network (VANET) is a vehicular specific type of a mobile ad-hoc network, to provide temporary communications among nearby vehicles. Mobile node of VANET consumes energy and resource with participating in the member of network. In a VANET, data replication and cooperative caching have been used as promising solutions to improve system performance. Existing cooperative caching scheme in a VANET mostly focuses on weak consistency is not always satisfactory. In this paper, we propose an efficient cache management scheme to maintain strong data consistency in a VANET. We make an adaptive scheduling scheme to broadcast Invalidation Report (IR) in order to reduce query delay and communication overhead to maintain strong data consistency. The simulation result shows that our proposed method has a strength in terms of query delay and communication overhead.

• The Transactions of the Korea Information Processing Society
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• v.5 no.6
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• pp.1390-1403
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• 1998

Database sharing system (DSS) refers to a system for high performance transaction processing. In DSS, the processing nodes are locally coupled via a high speed network and share a common database at the disk level. Each node has a local memory, a separate copy of operating system, and a DB'\fS. To reduce the number of disk accesses, the node caches database pages in its local memory buffer. However, since multiple nodes may be simultaneously cached a page, cache consistency must be cnsured so that every node can always access the'latest version of pages. In this paper, we propose efficient cache consistency schemes in DSS, where the database is logically partitioned using primary copy authority to reduce locking overhead, The proposed schemes can improve performance by reducing the disk access overhead and the message overhead due to maintaining cache consistency, Furthermore, they can show good performance when database workloads are varied dynamically.