Event Sourcing

In most applications, databases store the current state of the system. For example, an Order Service might store an order with the following information:

This tells us the current state of the order, but it doesn't explain how the order reached that state. Was the order created successfully? Was payment processed? Was inventory reserved? Did shipping fail and get retried? To answer these questions, we would need additional audit logs, history tables, or events.

Event Sourcing takes a different approach. Instead of storing only the current state, it stores the sequence of events that produced that state.

Every important state change is recorded as an event, and the current state can be reconstructed by processing those events in order. This approach is particularly useful in systems where history, traceability, and complex business workflows matter. Let's understand how event sourcing works, its relationship with microservices, and when it makes sense to use it.