Consistency in hindsight: A fully decentralized STM algorithm

Abstract

Software transactional memory (STM) algorithms often rely on centralized components to achieve atomicity, isolation and consistency. In a distributed setting, centralized components are undesirable as they impair scalability. This paper presents Decent STM, a fully decentralized object-based STM algorithm. It relies on mostly immutable data structures, which are well-suited for replication and migration. It is the first decentralized STM implementing snapshot isolation semantics. A novel randomized consensus protocol guarantees consistency of the mutable parts. Transactions may proceed tentatively before consensus has been reached. Object versioning ensures consistency in hindsight. Thus, atomic code sections never block during execution. The evaluation of benchmarks shows that the guaranteed success of reads more than compensates for the higher conflict rate during commit.