A Framework for Access Methods for Versioned Data
This paper presents a framework for understanding and constructing access methods for versioned data. Records are associated with version ranges in a version tree. A minimal representation for the end set of a version range is given. We show how, within a page, a compact representation of a record can be made using start version of the version range only. Current-version splits, version-and-key splits and consolidations are explained. These operations preserve an invariant which allows visiting only one page at each level of the access method when doing exact-match search (no backtracking). Splits and consolidations also enable efficient stabbing queries by clustering data alive at a given version into a small number of data pages. Last, we survey the methods in the literature to show in what ways they conform or do not conform to our framework. These methods include temporal access methods, branched versioning access methods and spatio-temporal access methods. Our contribution is not to create a new access method but to bring to light fundamental properties of version-splitting access methods and to provide a blueprint for future versioned access methods. In addition, we have not made the unrealistic assumption that transactions creating a new version make only one update, and have shown how to treat multiple updates.
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