Modelling replication protocols with actions and constraints

We describe a number of replication algorithms in a unified model based on actions and constraints. Applications submit actions (operations) to be executed and arbitrary constraints on those actions; object invariants are also expressed as constraints; and replication protocols impose further constraints. Any given site executes the actions it knows according to a schedule that satisfies the constraints. The goal of a protocol is to add constraints until its schedules are consistent. A replication protocol is consistent, if it maintains a local safety invariant (schedules are sound), a global invariant (local decisions do not conflict), and is live (every action eventually stabilises at all sites). Contact: Marc Shapiro, Microsoft Research Ltd, 7 JJ Thomson Ave., Cambridge CB3 0FB, United Kingdom. Tel. +44 1223 479 739, fax +44 1223 479 999. Email: [email protected] Paper to be considered for both regular and brief announcement tracks. None of the authors is a student.