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Event system evolution A Scientific Study on Event Sourcing, Lessons from Industry

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Michiel Lead Software Architect @ AFAS Software PhD candidate @ University Utrecht [email protected] @michielovereem https://movereem.nl Overeem

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25 engineers with 103 years of combined experience

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RQ2 RQ3 RQ1 What types of systems apply event sourcing and why? How can event sourced systems be defined? What are the challenges faced in applying event sourcing?

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THE PROBLEM

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Project administration Marketing automation Website building Payment processing Content management Classified advertising …

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Rationale Flexibility Complexity Trending Audit Immutability Strict Cut-off Mutable Technology .NET JVM PHP Ruby,Scala,Go

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DDD Yes No MSA Yes No CQRS Yes No

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THE SOLUTION

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“business analysts are telling us what the events should be.” (E5) “you capture business changes as a flow of events, you align these events with real world events.” (E11)

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internal versus external events

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state propagation events

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A single transaction crossing event & query database

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THE CONSEQUENCES

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Steep learning curve Learning curve Finding your way

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Missing tools Related to the learning curve? Or the trend?

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Projections Things might take a while

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User Privacy Can we forget things?

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Evolution Small steps, but how to stay stable?

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Versioned Events Weak Schema Upcasters In-Place Copy- Transform 14/24 5/24 12/24 11/24 2/24

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Michiel Overeem, Marten Spoor, Slinger Jansen, and Sjaak Brinkkemper. (2021). An Empirical Characterization of Event Sourced Systems and Their Schema Evolution - Lessons from Industry. In Journal of Systems and Software In Practice volume 178 (2021), 110970. https://dx.doi.org/10.1016/j.jss.2021.110970

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Michiel [email protected] @michielovereem https://movereem.nl Overeem Event sourcing is a pattern that solves the three problems that modern systems face: flexibility, complexity, and reliability. These benefits give enough reason to incorporate event sourcing in modern systems.