Event Sourcing with John Bywater


October 15th, 2017

1 hr 8 mins 26 secs

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About this Episode


The way that your application handles data and the way that it is represented in your database don’t always match, leading to a lot of brittle abstractions to reconcile the two. In order to reduce that friction, instead of overwriting the state of your application on every change you can log all of the events that take place and then render the current state from that sequence of events. John Bywater joins me this week to discuss his work on the Event Sourcing library, why you might want to use it in your applications, and how it can change the way that you think about your data.


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  • Your host as usual is Tobias Macey and today I’m interviewing John Bywater about event sourcing, an architectural approach to make your data layer easier to scale and maintain.


  • Introductions
  • How did you get introduced to Python?
  • Can you start by describing the concept of event sourcing and the benefits that it provides?
  • What is the event sourcing library and what was your reason for starting it?
  • What are some of the reasons that someone might not want to implement an event sourcing approach in their persistence layer?
  • Given that you are storing a record for each event that occurs on a domain object, how does that affect the amount of storage necessary to support an event sourced application?
  • What is the impact on performance and latency from an end user perspective when the application is using event sourcing to render the current state of the system?
  • What does the internal architecture and design of your library look like and how has that evolved over time?
  • In the case where events are delivered out of order, how can you ensure that the present view of an object is reflected accurately?
  • For someone who wants to incorporate an event sourcing design into an existing application, how would they do that?
  • How do you manage schema changes in your domain model when you need to reconstruct present state from the beginning of an objects event sequence?
  • What are some of the most interesting uses of event sourcing that you have seen?
  • What are some of the features or improvements that you have planned for the future of you event sourcing library?

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The intro and outro music is from Requiem for a Fish The Freak Fandango Orchestra / CC BY-SA