A query optimization assistant for XPath

Abstract

We demonstrate a generic and extensible cost-based optimization and execution system for XPath queries, named GeCOEX, using a comprehensive suite of query analyzing and administrative tools, named QuOAX. GeCOEX supports many different physical operator implementations and XML storage engines and is agnostic to the underlying physical data model. Its optimizer is the first generic cost-based optimizer for XPath queries that always picks the cheapest estimated plan, among a very large number of possible plans, for a wide range of XPath queries and different datasets in a very small fraction of the time required for efficient execution. The QuOAX suite provides administration tools that allow the user to add new -or deactivate already deployed -physical operator implementations, physical operator cost models and rewriting rules and also to make use of different XML storage and XML statistics estimators. QuOAX also provides query plan analysis and visualization tools that allow users to visualize the physical plan chosen by the optimizer or all possible generated physical plans for a given query and to execute any of those plans. QuOAX helps users to i) easily test new XPath processing techniques, comparing them directly with existing ones and identifying the situations to which they show promise, ii) improve the effectiveness of the optimizer and iii) find out the appropriate access methods or indices that are beneficial for a specific workload.