# ADR-001: Use PostgreSQL for Primary Database

## Status
Accepted

## Context
We need a database for our e-commerce platform that handles:
- Complex transactions (orders, payments, inventory)
- ACID compliance requirements
- Relational data (users, products, orders)
- Expected scale: 100K users, 10K orders/day

## Decision
We will use PostgreSQL as our primary database.

## Alternatives Considered

### MongoDB
- **Pros**: Flexible schema, horizontal scaling
- **Cons**: Weaker transaction support, eventual consistency
- **Why rejected**: We need strong ACID guarantees for financial transactions

### MySQL
- **Pros**: Mature, widely used, good performance
- **Cons**: Less advanced features than PostgreSQL
- **Why rejected**: PostgreSQL's JSON support and advanced indexing better fit our needs

## Consequences

### Positive
- Strong ACID compliance for financial transactions
- Rich query capabilities (CTEs, window functions)
- JSON support for flexible product attributes
- Mature ecosystem and tooling

### Negative
- Vertical scaling limitations (can be mitigated with read replicas)
- More complex to operate than managed NoSQL solutions
- Learning curve for team members unfamiliar with SQL

## Implementation Notes
- Use Prisma ORM for type-safe database access
- Set up read replicas for scaling reads
- Use connection pooling (PgBouncer)

## Related Decisions
- ADR-002: Use Prisma ORM
- ADR-005: Database migration strategy

## Date
2024-01-15

## Authors
@alice, @bob

docs/adr/
├── README.md
├── 0001-use-postgresql.md
├── 0002-use-prisma-orm.md
├── 0003-adopt-microservices.md
├── 0004-use-react-frontend.md
└── template.md

# Install
npm install -g adr-log

# Create new ADR
adr new "Use PostgreSQL for primary database"

# List all ADRs
adr list

# Generate table of contents
adr generate toc

# Install
npm install -g log4brains

# Initialize
log4brains init

# Preview
log4brains preview

# Build static site
log4brains build

# Use Tailwind CSS for styling

**Status**: Accepted
**Date**: 2024-01-15

## Decision
Use Tailwind CSS for all component styling.

## Rationale
- Utility-first approach speeds up development
- Consistent design system
- Smaller bundle size with PurgeCSS
- Team already familiar with it

## Consequences
- Need to learn Tailwind conventions
- HTML can become verbose
- Harder to share styles across projects

# ADR-003: Adopt Microservices Architecture

## Status
~~Accepted~~ **Superseded by ADR-010**

## Superseded By
[ADR-010: Return to Modular Monolith](0010-modular-monolith.md)

## Original Decision
[Keep original content for historical reference]

## Why Superseded
After 2 years of microservices:
- Operational complexity exceeded benefits
- Team size (5 engineers) too small to manage 12 services
- Network latency impacting user experience
- Distributed tracing and debugging challenges

See ADR-010 for new approach.

## ADR Review Checklist

- [ ] **Context Clear**: Is the problem well-defined?
- [ ] **Alternatives Listed**: Were other options considered?
- [ ] **Trade-offs Analyzed**: Pros and cons documented?
- [ ] **Consequences Identified**: Both positive and negative?
- [ ] **Stakeholders Consulted**: Relevant teams reviewed?
- [ ] **Implementation Plan**: Next steps clear?
- [ ] **Date and Authors**: Documented?

## PR Description

This PR implements the decision from [ADR-005: Use Redis for caching](../docs/adr/0005-redis-caching.md)

Changes:
- Add Redis client
- Implement cache layer
- Update documentation

// Per ADR-003, we use JWT for authentication
// See: docs/adr/0003-jwt-authentication.md
export function verifyToken(token: string) {
  // ...
}