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Abstract : |
In this paper, we analyze the performance of dynamic finite versioning (DFV) schemes for concurrent transaction and query processing, where a finite number of consistent snapshots can be derived for query access. We develop analytical models based on a renewal process approximation to evaluate the performance of DFV using M 2 snapshots. The storage overhead and obsolescence faced by queries are measured. Simulation is used to validate the analytical models and to evaluate the trade-offs between various strategies for advancing snapshots when M? 2. The results show that (1) the analytical models match closely with simulation; (2) both the storage overhead and obsolescence are sensitive to the snapshot-advancing strategies, especially for M? 2 snapshots; and (3) generally speaking, increasing the number of snapshots demonstrates a trade-off between storage overhead and query obsolescence. For cases with skewed access or low update rates, a moderate increase in the number of snapshots beyond 2 can substantially reduce the obsolescence, while the storage overhead may increase only slightly, or even decrease in some cases. Moreover, for very low update rates, a large number of snapshots can be used to reduce the obsolescence to almost zero without increasing the storage overhead. 1, |
