• The Journal of the Korea Contents Association
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• v.5 no.6
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• pp.49-56
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• 2005

To reduce server bottlenecks in client-server computing, each client may have its own cache for later reuse. The pessimistic approach for cache management protocol leads to unnecessary waits, because, it can not be commit a transaction until the transaction obtains all requested locks. In addition, optimistic approach tends to make needless aborts. This paper suggests an efficient optimistic protocol that overcomes such shortcomings. In this paper, we present a simulation-based analysis on the performance of our scheme with other well-known protocols. The analysis was executed under the Zipf workload which represents the popularity distribution on the Web. The simulation experiments show that our scheme performs as well as or better than other schemes with low overhead.

• Journal of KIISE:Databases
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• v.30 no.4
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• pp.397-407
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• 2003

Transactions of updating spatial dta with mobile clients are log transactions because a user disconnected from a server surveys real features and updates them. In this environment, it is appropriate to exploit the optimistic approach based on the validation test in order to control the concurrency of transactions. On the contrary, the pessimistic concurrency control scheme makes transactions wait for a long time due to the lock. In this paper, we propose the surrogate transaction model and implement its manager for the S-S-M(Server-Surrogate PC-Mobile Client) structure which is appropriate for updating spatial data in mobile environments. In the S-S-M structure, the mobile client communicates with the server by the surrogate PC. We extend the validation condition in consideration of spatial relationships between spatial objects in this model. We also present the commit protocol where the user of a surrogate PC adjusts objects of the conflicted surrogate transaction to minimize costs for the abortion of the transaction.