Non-Monotonic Snapshot Isolation

We study two important properties for the scalability of a replicated system: genuine partial replication (GPR) and snapshot isolation (SI). We prove that these properties are incompatible. To side step this impossibility result, we propose a novel consistency criterion called Non-Monotonic Snapshot Isolation (NMSI). NMSI retains the most important properties of SI: read-only transactions always commit, and two concurrent write-con icting updates never both commit. We also introduce a GPR protocol that ensures NMSI, and commits transactions faster and/or contacts fewer replicas than previous systems. Key-words: oncurrency control, database machines, protocols, replicated databases, transaction processing ∗ The work presented in this paper has been partially funded by ANR projects Prose and Concordant. ha l-0 06 43 43 0, v er si on 1 22 N ov 2 01 1