PADRE: A Policy Architecture for building Data REplication systems

This paper presents Padre, a new policy ar- chitecture for developing data replication systems. Padre simplifies design and implementation by embodying the right abstractions for replication in widely distributed systems. In particular, Padre cleanly separates the prob- lem of building a replication system into the subprob- lems of specifying liveness policy and specifying safety policy, and it identifies a small set of primitives that are sufficient to specify sophisticated systems. As a result, building a replication system is reduced to writing a few liveness rules in a domain-specific language to trigger communication among nodes and specifying safety pred- icates that define when the system must block requests. We demonstrate the flexibility and simplicity of Padre by constructing a dozen substantial and diverse systems, each using just a few dozen system-specific policy rules. We demonstrate the agility that Padre enables by adding new features to several systems, yielding significant per- formance improvements; each addition required fewer than ten additional rules and took less than a day.