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Modelling replication protocols with actions and constraints
{ Thu, 4 Dec 2003, 11h30 }

By: Marc Shapiro  [ show info ]

I will describe a formal model of replicated-data systems, based on actions and constraints. An action models a data transformation, and a constraint models an invariant. The same model describes different levels in a unified fashion: - A client application requests updates (actions) that are related to one another in various ways, e.g. by causal dependence or atomicity (constraints). - Concurrent updates may conflict, i.e. violate object invariants (more constraints). - The replication protocol transfers actions and orders them (adding other constraints). - Each site executes the actions it knows, according to some serial schedule that satisfies the constraints it knows. - The whole system must enforce consistency. Within the model we give three different definitions of consistency: (1) the intuitive, "declarative" notion of eventual consistency, (2) an "operational" definition based on equivalence of local schedules, and (3) a property of local information called mergeability. We show the three definitions are equivalent. If time permits, I will analyse a few well-known replication protocols in the framework.

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