ADR 0003: Use CQRS Light

Status

Accepted

Context

The catalog module needs a clean read path and cacheable projections, but a separate read database would be unnecessary complexity for this showcase.

Decision

Use CQRS light in catalog:

• command service owns stock reservation
• query service returns immutable ProductView projections
• both paths use the same PostgreSQL database
• Redis caches read operations through Spring Cache

Consequences

Benefits:

• clearer read/write responsibilities
• cacheable query model
• no fake distributed consistency story

Trade-offs:

• reads and writes still share one database schema
• cache invalidation must be handled by command operations
• projections remain simple and local to catalog