Event sourcing is a well-known pattern gaining widespread adoption among microservices developers as a way of adhering to the "database per service" principle. It relies upon an append-only store to record the entire sequence of actions taken upon the system rather than a more traditional relational database. It is often combined with the CQRS, which uses materialized views to convert event-based data from one (or more) sources into a format that is more suitable for querying.

In this talk, we will present different approaches to calculating these materialized views using a simple microservice application that demonstrates the various techniques. We will discuss the pros and cons of each approach and highlight some of the common pitfalls and best practices we have learned from implementing these patterns at scale.