Perturbation-Resilient Atomic Commit Protocols for Mobile Environments (2010)

The support of distributed atomic transactions is a key requirement for many current mobile applications. Atomicity is a fundamental property ensuring that all nodes reach a consistent outcome. For this, distributed mobile transactions fundamentally require perturbation-resilient atomic commit protocols. This is challenging as mobile environments are typically characterized by frequent network and node perturbations. The environmental constraints on mobile transaction participants and wireless links may increase the resource blocking time of fixed participants. Moreover, frequent node and link failures complicate the design of atomic commit protocols by increasing both the transaction abort rate and resource blocking time. Hence, the deployment of classical commit protocols is not necessarily applicable to distributed mobile environments. Existing protocols ensuring strict atomicity in mobile environments are either bound to very narrow and specific application scenarios or have poor commit rates, high message overhead or a blocking behavior. In order to cope with different application scenarios, we first identify three classes of mobile environments: infrastructure-based, ad-hoc and generic. Furthermore, we consider and comprehensively classify the perturbations of the wireless mobile environment into classes according to their impact on the outcome of commit protocols and on their blocking behavior. To tolerate these perturbation classes, perturbation-tolerant mechanisms are provided. Based on these mechanisms, we develop a family of perturbation-tolerant atomic commit protocols with minimal resource blocking time and optimized transaction commit rates. For the infrastructure-based mobile environment, we propose an approach that decouples the commit of mobile participants from that of fixed participants -- beyond using the strengths of existing approaches. Consequently, the commit set is reduced to a set of entities in the fixed network. Thus, the commit can easily be supported by any traditional atomic commit protocol. For the ad-hoc mobile environment, we present a commit approach that supports a significantly wider range of mobility patterns and partitioning scenarios than existing protocols. Our approach is based on a novel coordination strategy using a flexible preselection of multiple coordinators among the participating nodes. Thus, the failure of a single coordinator is tolerated in the presence of network partitioning. For the generic mobile environment, we develop an approach that takes advantage of accessing the wired infrastructure if available, by choosing reliable infrastructure nodes for coordinating transactions. If the access to the wired infrastructure is unavailable, our approach adapts itself to the resulting ad-hoc environment. We evaluated our framework and the algorithms presented in this thesis via extensive simulations and experiments. They validated the efficiency and scalability of the developed solutions and additionally emphasized their resilience to the considered environmental, network and node perturbations by minimizing resource blocking times and optimizing transaction commit rates. Furthermore, they confirmed the suitability of our solutions to a wide range of mobile applications.