Scheduling Update and Query Transactions under Quality Contracts in Web-Databases ∗

modern web-database systems, users typically perform read- only queries, whereas all data updates are performed in the back- ground, concurrently with queries. In this paper, we present the concept of Quality Contracts which allows individual users to ex- press their preferences by assigning "profit" values to their ex- pected Quality of Service (QoS) and Quality of Data (QoD). We propose an adaptive algorithm, called QUTS, to maximize the to- tal profit from submitted Quality Contracts, which essentially opti- mizes the overall user satisfaction. QUTS address the problem of prioritizing the scheduling of updates (crucial to QoD) over queries (crucial toboth QoSand QoD) using atwo-level scheduling scheme that dynamically allocates CPU resources to updates and queries. We present the results of an extensive experimental study using real data (taken from a stock information web site), where we show that QUTS performs better than baseline algorithms under the entire spectrum of quality contracts; QUTS adapts fast to changing work- loads and QUTS' sensitivity to its two parameters is negligible.

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