Monday July 14, 2003
To address such problem, in this talk I will explore the spectrum between the traditional two extremes of strong consistency and optimistic consistency, and propose the concept of continuous consistency. Continuous consistency overcomes the fundamental obstacle in wide-area replication by allowing applications to choose middle points on the consistency spectrum. Specifically, I will describe the design of the TACT middleware that enables dynamically tunable consistency levels. I will also discuss the TACT implementation and performance evaluation across the Internet. The results show that applications can achieve significant semantics and performance benefits using the TACT middleware.
Next, I will explore the consistency model's effects on system availability, both theoretically and experimentally. I will first discuss a tight availability upper bound for all consistency protocols. Then I will describe how I measure the availability of existing consistency protocols in both wide-area deployment and a local emulation environment, and compare the results to the upper bound. I will show that: i) simple optimizations can significantly improve availability; and ii) for small-scale systems, the optimized protocols can approach the upper bound in my experiments.
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