A Modular and Efficient Past State System for Berkeley DB

Applications often need to analyze past states to predict trends and support audits. Adding efficient and nondisruptive support for consistent past-state analysis requires after-the-fact modification of the data store, a significant challenge for today’s systems. This paper describes Retro, a new system for supporting consistent past state analysis in Berkeley DB. The key novelty of Retro is an efficient yet simple and robust implementation method, imposing 4% worst-case overhead. Unlike prior approaches, Retro protocols, backed by a formal specification, extend standard transaction protocols in a modular way, requiring minimal data store modification (about 250 lines of BDB code).