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Eventually Consistent Computations Christopher S. Meiklejohn Peter Van Roy

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large-scale computation without synchronization

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large-scale computation without synchronization

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large-scale computation without synchronization

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large-scale computation without synchronization

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the Plan

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conflict-free replicated data types (CRDTs)

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distributed deterministic dataflow

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compose CRDTs using deterministic data flow

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the Data Types

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state-based conflict-free replicated data types

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state-based conflict-free replicated data types

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semantic resolution

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semantic resolution “In all such systems, we find developers spend a significant fraction of their time building extremely complex and error-prone mechanisms to cope with eventual consistency and handle data that may be out of date.” “F1: A Distributed SQL Database That Scales” (VLDB 2013)

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strong eventual consistency

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strong eventual consistency “Systems in which replica conflicts are impossible by design exhibit Strong Eventual Consistency (SEC).” - Wikipedia, ”Eventual Consistency”

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state-based conflict-free replicated data types

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bounded Join-Semilattices* * drastically simplified example

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bounded Join-Semilattices* [1] [6] [2] [1,6] [6,2] [1,6,2] [1,2] [] * drastically simplified example

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the Programming Model

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the Research

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the Research

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the Constraint Store* σ P1 P2 Pn-1 Pn … * monotonic; single-assignment

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the Constraint Store* σ P1 P2 Pn-1 Pn … * monotonic; single-assignment read(X) bind(X, 1)

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the Constraint Store* σ P1 P2 Pn-1 Pn … * monotonic; lattice variables

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the Constraint Store* σ P1 P2 Pn-1 Pn … * monotonic; lattice variables read(X) bind(X, 1) bind(X, 2) read(X, 2)

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the Distribution Model

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the Distribution Model

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the Distribution Model 4 6 5 the Application 1 3 2 read(X) bind(Y, 2) read(Y) bind(X, 1)

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the Distribution Model

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1 3 2 the Application the Distribution Model bind(X, 1) 1 2 3 ok

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1 3 2 the Application the Distribution Model

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1 3 2 the Application the Distribution Model register(application) 1 2 3 ok A’ A’

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1 3 2 the Application the Distribution Model

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1 3 2 the Application the Distribution Model execute(application) 1 2 3 {ok, Result} A’ A’ ⊔

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the Distribution Model 1 3 2 4 6 5 the Application

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the Distribution Model 1 3 2 4 6 5 the Application 1 4 ⊕ 2 5

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the Distribution Model 1 3 2 4 6 5 the Application 2 5

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the Distribution Model 1 3 2 4 6 5 the Application 1 4 ⊕ 2 5 5 2 ⊔ ⊔

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the Examples

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C1 C2 C3 S1 S2 M1 M2 M3 the Ad Counter the Diagram

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C1 C2 C3 S1 S2 M1 M2 M3 view inc rem view view the Ad Counter the Diagram

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the Secondary Index the Program

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the Secondary Index the Program filter(fun even/1)* (* computes -CRDT) [1, 2] [2, 6] [1, 2, 5] [2] [2, 6] [2, 6]

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the Secondary Index the Diagram

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⊕ the Secondary Index the Diagram 3 1 2 ⊔

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the Conclusion

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sequential composability

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divergence control

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moving computation to the client

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thanks peter Van Roy russell Brown marc Shapiro annette Bieniusa manuel Bravo jordan West sean Cribbs carlos Baquero nuno Preguica joao Leitao ryan Zezeski tom Santero peter Alvaro image credits: Wikipedia, “The Village (The Prisoner)” slides: https://speakerdeck.com/cmeiklejohn/eventually-consistent-computations prototype: https://github.com/cmeiklejohn/derflow

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be seeing you Christopher S. Meiklejohn @cmeik