Micro Services - Database Design Pattern

In a microservices architecture, each microservice typically manages its own database. This approach offers several benefits, such as improved scalability and independence. However, it also introduces challenges, particularly around data sharing and consistency. To address these challenges, several complementary patterns can be employed: 

Event-Driven Pattern

In an event-driven architecture, each microservice saves data in its own database. The limitation of this approach is the difficulty in sharing data between microservices. To overcome this, microservices can connect with each other and create a copy of data from other microservices, storing it as a local cache. This allows microservices to access the necessary data without directly querying another service's database, thus reducing inter-service dependencies and improving performance. 

Event Sourcing Pattern

Event sourcing involves storing data as a series of events. This pattern is straightforward to implement in a monolithic database but is also feasible with microdatabases. Instead of storing the current state of an entity, all changes (events) to the entity are stored. To determine the latest state of the data, all events must be replayed and evaluated. While this approach can impact performance and increase storage requirements, it offers the advantage of easy data rollback by replaying events up to a certain point. Event sourcing provides a detailed audit trail and can be useful for debugging and compliance purposes. 

CQRS (Command and Query Responsibility Segregation) Pattern

CQRS separates the reading and writing of data into different models. In this pattern, there are distinct services for handling commands (writes) and queries (reads). The write and read databases are different, and a synchronization mechanism is required to keep them in sync. This separation allows for optimized read and write operations, as each can be scaled and optimized independently. However, ensuring data consistency between the write and read databases is critical and can add complexity to the system.