Command Query Responsibility Segregation (CQRS)
Separate read and write data models: Write-optimized relational stores, read-optimized projection views (Elasticsearch/Redis), projection lag mitigation, and eventual consistency.
01.1. Why Segregate Commands and Queries?
In traditional database architectures, a single schema serves both write transactions and complex analytical queries. As systems scale, this dual responsibility creates irreconcilable architectural friction:
- Write Demands: Require strict 3NF normalization, foreign key constraints, row-level ACID locks, and low write amplification to guarantee invariant integrity.
- Read Demands: Require denormalized schemas, multi-table joins, nested document structures, inverted indexes for full-text search, and in-memory caches to serve sub-millisecond query responses.
Command Query Responsibility Segregation (CQRS) resolves this conflict by dividing the application into two completely independent architectural models:
- Commands (Write Path): Execute business logic, enforce domain invariants, and mutate normalized transactional storage.
- Queries (Read Path): Fetch pre-aggregated, denormalized data structures from dedicated read-optimized storage engines.
CQRS Architecture: Segregated Read and Write Pipelines
CQRS Architecture: Segregated Read and Write Pipelines
Separating normalized write models from high-throughput denormalized query stores via asynchronous projections.
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