CQRS Design Pattern

Command Query Responsibility Segregation (CQRS) separates read and write operations into distinct data models and databases, enabling independent scaling, improved security, and better performance. The pattern addresses challenges in both monolithic and microservice architectures by decoupling data access patterns. Implementation approaches range from database-native replication (like PostgreSQL streaming replication) to Change Data Capture solutions using Debezium. A practical voting application demonstrates three replication scenarios: PostgreSQL-to-PostgreSQL using native replication, PostgreSQL-to-MySQL using Debezium JDBC sink connector, and PostgreSQL-to-QuestDB using vendor-specific sink connectors. Debezium simplifies CQRS implementation in heterogeneous environments by capturing database changes in real-time and propagating them across different database technologies through Kafka Connect.