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Taming the Tiger: How to Cope with Real Database Products in Transactional Federations for Internet Applications

Data consistency in transactional federations is a key requirement of advanced E-service applications on the Internet, such as electronic auctions or real-estate purchase. Federated concurrency control needs to be aware of the fact that virtually all commercial database products support sub-serializability isolation levels, such as Snapshot Isolation, and that applications make indeed use of such local options. This paper discusses the problems that arise with regard to global serializability in such a setting, and proposes solutions. Protocols are developed that can guarantee global serializability over component systems that provide only weaker isolation levels. A full-fledged implementation is presented that makes use of OrbixOTS and runs on top of Oracle8i and O2 databases. Performance measurements with this prototype indicate the practical viability of the developed methods.