Architectural Comparison & Data Modeling:
1. SQL (Relational Databases - PostgreSQL, MySQL):
- Data Model: Structured tables with strict schemas, relations, and foreign keys.
- Scaling: Scales vertically (larger CPU/RAM); reads scale horizontally via read replicas. Sharding writes across nodes requires complex application logic.
- Guarantees: Strong ACID transactional consistency. Excellent for complex multi-table joins, financial ledgers, and interconnected business domains.
- Best For: Billing systems, inventory management, user identities, and any domain requiring relational integrity.
2. NoSQL Databases:
- Key-Value (Redis, DynamoDB): Extreme read/write throughput on primary keys; sub-millisecond latency for caches and session stores.
- Document (MongoDB): Flexible JSON-like schemas; ideal for hierarchical data, user profiles, and content management.
- Columnar (Cassandra, ClickHouse): Massive horizontal write scaling and high-performance analytical aggregations.
- Trade-offs: Sacrifices complex relational joins and full multi-table ACID transactions for horizontal partitioning, high availability, and flexible schemas.