The Path Towards Simplifying Consistency in Distributed Systems

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Caitie McCaffrey Distributed Systems Engineer caitiem.com @caitie

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Distributed Systems Engineer Feral Concurrency Control Programmer Caitie McCaffrey

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2015

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2015 “Application-level Mechanisms for maintaining database integrity”

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Halo 4 Statistics Service Halo 4 Statistics Service Record & Aggregate Statistics From Every Multiplayer Halo Game a User Plays

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Halo 4 Statistics Service

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Observability at Twitter Make Dashboards & Alerts Always Available

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Cmd Line Tool Viz / Dashboad Alerting Svc Cuckoo-Read Cuckoo-Write Indexing Svc Relay Svc Twitter Front End Twitter Svc Twitter Statsite Twitter Svc Twitter Svc Scribe Collection Agent HDFS Manhattan Database Public Cloud Observability at Twitter

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Notify Users When We Receive Abuse Reports

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Notify Users If An Action is Taken

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Report Events Stream Modification Events Stream Enrollment Events Stream Listener Service Daemons Service Executor Service Notification Events Stream Notification Service Manhattan Macaw

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Feral Concurrency Control

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Service Service Service Monoliths

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The Rise of NoSQL

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Microservices

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State of Affairs

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Linearizable Sequential Causal Pipelined Random Access Memory Read Your Write Monotonic Read Monotonic Write Write From Read Consistency Models

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Can We Do Better?

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Finance & Accounting

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VisiCalc 1979

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1983 Lotus 123

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1987 Excel

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& Standardization Computer Aided Computation

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Standardization for Consistency in Distributed Systems

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1988

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1988 “We believe the form of communication that is needed is remote procedure call with at- most-once semantics”

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1988 “An adequate language must provide a modular, reasonably automatic method for achieving consistency ”

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Branch B Account 789: $250 Branch A Account 123 : $100 Account 456: $50 SubAction: Deposit (123, 50) Transfer Action SubAction: Withdraw(789, 50) Transfer Deposit Withdraw enter topaction coenter action branchA.Deposit(123, 50) action branchB.Withdraw(789, 50) end end

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What about Spanner?

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2015

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2015 “The biggest barrier…is that consistency mechanisms must integrate across many stateful services”

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Microservices

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CRDTs * Stolen from Chris Meiklejohn in practice

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CRDTs * Stolen from Chris Meiklejohn in practice

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There Is No One Size Fits All Consistency Model

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Mixed Consistency Data Stores Manhattan

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Computer Aided Computation for Consistency in Distributed Systems

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2016

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Bank Application Bank Account must be > 0 Deposit Money Withdrawal Money

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‘Cause I’m Strong Enough: Reasoning About Consistency Choices in Distributed Systems

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Deﬁne Invariants & Actions Deposit Money Withdrawal Money Determine Consistency Required Bank Account > 0 Eventual Consistency Strong Consistency Code Generation?