[FEATURE] PostgreSQL Database Adapter Implementation

[HaxoLabs]

Feature Summary

Implement a PostgreSQL adapter that provides SQL database access through DBX's unified API, enabling relational database operations alongside Redis and MDBX.

Motivation

PostgreSQL support expands DBX into relational database scenarios, making it a true polyglot database proxy. This enables complex queries, ACID transactions, and structured data management.

Detailed Description

Create a PostgreSQL adapter that includes:

• Connection pooling with deadpool-postgres
• SQL query execution through DBX API
• Table management operations
• Transaction support
• Index management
• Integration with DBX authentication and routing
• Query result caching

Proposed Solution

1. Adapter Structure: Create crates/adapter/postgres/
2. Connection Pool: Use deadpool-postgres for connection management
3. Query Interface: Implement SQL query execution endpoints
4. ORM Integration: Consider sqlx for type-safe queries
5. Caching: Implement query result caching

Alternative Solutions

• Generic SQL adapter supporting multiple databases
• MySQL adapter instead of PostgreSQL
• NoSQL document interface over PostgreSQL JSON

Additional Context

PostgreSQL is the most popular open-source relational database and would significantly expand DBX's use cases.

Implementation Notes

• Use async PostgreSQL client with connection pooling
• Implement proper SQL injection prevention
• Support prepared statements
• Handle PostgreSQL-specific data types
• Implement query result streaming for large datasets

Acceptance Criteria

• Complete PostgreSQL adapter in crates/adapter/postgres/
• Connection pooling with configurable parameters
• SQL query execution endpoints
• Table management operations (create, drop, alter)
• Transaction support (begin, commit, rollback)
• Index management operations
• Query result caching with configurable TTL
• Integration with existing authentication
• Query parameter binding for security
• Unit tests with >85% coverage
• Integration tests with PostgreSQL test database
• Performance benchmarks
• Documentation with SQL examples
• Migration guide from direct PostgreSQL usage

Priority

• Medium

Checklist

• I have searched existing issues to ensure this is not a duplicate
• I have provided sufficient detail about the requested feature
• I have considered potential implementation challenges
• This feature aligns with the project's goals