ADR-004: PostgreSQL for Message Persistence

Status

Accepted

Context

Wisdoverse Nexus needs persistent storage for:

• Messages (chat history)
• Rooms (conversation containers)
• Members (user/ai identities)
• Future: Files, reactions, threads

Requirements:

• ACID compliance (reliability)
• JSON support (flexible message content)
• Full-text search (message search)
• Scalability (future growth)

Options considered:

• MongoDB: Flexible schema, weaker consistency
• PostgreSQL: Strong consistency, mature ecosystem
• ScyllaDB: High write throughput, complex operations

Decision

Use PostgreSQL as the primary data store.

Consequences

Positive

• ACID compliance for reliability
• JSONB for flexible message content
• Full-text search built-in
• Mature Rust ecosystem (SQLx)
• Easy to find expertise

Negative

• Horizontal scaling more complex than NoSQL
• Schema migrations require planning

Mitigation

• Use connection pooling (SQLx)
• Design for future sharding if needed
• Use SQLx migrations for schema management