ParTAC: A Partition-Tolerant Atomic Commit Protocol for MANETs

The support of distributed atomic transactions in Mobile Ad-hoc Networks (MANET) is a key requirement for many mobile application scenarios. Atomicity is a fundamental property that ensures that all nodes decide a consistent outcome. As MANETs are characterized by frequent perturbations due to network partitioning and the fragility of nodes, providing atomicity is challenging. Existing protocols that ensure strict atomicity in MANETs are either bound to specific mobility pattern or based on building blocks such as consensus or group membership, not allowing arbitrary partitions or requiring exact knowledge about the members of a partition. These assumptions limit the deployment of these protocols to very restricted MANET scenarios, and may lead to poor commit rate, high message overhead or blocking related to intolerably long Commit/Abort decision times. In this paper, we present the first Partition-Tolerant Atomic Commit protocol (ParTAC) for MANETs which does not rely on consensus or group partition membership. As a consequence, ParTAC supports a significantly wider range of mobility patterns and partitioning scenarios than existing protocols. To reduce Commit/Abort decision times and prevent the protocol from blocking, ParTAC follows a best-effort strategy by defining a lifetime for every transaction after which the transaction is aborted. Further, we introduce a new coordination strategy based on a flexible preselection of multiple coordinators among the participating nodes. Thus, the failure of a single coordinator can be tolerated in the presence of network partitioning. Moreover, transactions can be aborted by any coordinator based on lifetime expiration. ParTAC is evaluated using simulations to demonstrate the performance of the protocol in terms of commit rate, message efficiency and Commit/Abort decision time.