In-Situ Cross-Database Query Processing

Today’s organizations utilize a plethora of heterogeneous and autonomous DBMSes, many of those being spread across different geo-locations. It is therefore crucial to have effective and efficient cross-database query processing capabilities. We present XDB, an efficient middleware system that runs cross-database analytics over existing DBMSes. In contrast to traditional query processing systems, XDB does not rely on any mediating execution engine to perform cross-database operations (e.g., joining data from two DBMSes). It delegates an entire query execution including cross-database operations to underlying DBMSes. At its core, it comprises an optimizer and a delegation engine: the optimizer rewrites cross-database queries into a delegation plan, which captures the semantics as well as the mechanics of a fully decentralized query execution; the delegation engine then deploys the plan to the underlying DBMSes via their declarative interfaces. Our experimental study based on the TPC-H benchmark data shows that XDB outperforms state-of-the-art systems (Garlic and Presto) by up to 6× in terms of runtime and up to 3 orders of magnitude in terms of data transfer.