Abstract: Support for Speculative Update Propagation and Mobility in Deno

This paper presents the transactional framework of Deno, an object replication system specifically designed for use in mobile and weakly-connected environments. Deno uses weighted voting for availability and pair-wise, epidemic information flow for flexibility. This combination allows the protocols to operate with less than full connectivity, to easily adapt to changes in group membership, and to make few assumptions about the underlying network topology. These features are all crucial to providing effective support for mobile and weakly-connected platforms. Deno has been implemented and runs on top of Linux and Windows NT/CE platforms. We use the Deno prototype to characterize the performance of two versions of Deno's protocol. The first version enables globally serializable execution of update transactions. The second supports a weaker consistency level that still guarantees transactionally consistent access to replicated data. The results show that our protocols either outperform or perform comparably to existing approaches, while achieving higher availability. Further, we show that the incremental cost of providing global serializability in this environment is low. Finally, we show that commit delays can be significantly decreased by allowing votes to be cast, and votes and updates to be disseminated, speculatively.