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# RFC-042: Implement Read Replicas for Analytics

**Status:** Draft | In Review | Accepted | Rejected | Implemented
**Author:** Alice ([email protected])
**Reviewers:** Bob, Charlie, David
**Created:** 2024-01-15
**Updated:** 2024-01-20
**Target Date:** Q1 2024

## Summary

Add PostgreSQL read replicas to separate analytical queries from transactional workload, improving database performance and enabling new analytics features.

## Problem Statement

### Current Situation

Our PostgreSQL database serves both transactional (OLTP) and analytical (OLAP) workloads:

- 1000 writes/min (checkout, orders, inventory)
- 5000 reads/min (user browsing, search)
- 500 analytics queries/min (dashboards, reports)

### Issues

1. **Performance degradation**: Analytics queries slow down transactions
2. **Resource contention**: Complex reports consume CPU/memory
3. **Blocking features**: Can't add more dashboards without impacting users
4. **Peak hour problems**: Analytics scheduled during business hours

### Impact

- Checkout p95 latency: 800ms (target: <300ms)
- Database CPU: 75% average, 95% peak
- Customer complaints about slow pages
- Product team blocked on analytics features

### Success Criteria

- Checkout latency <300ms p95
- Database CPU <50%
- Support 2x more analytics queries
- Zero impact on transactional performance

## Proposed Solution

### High-Level Design

┌─────────────┐ │ Primary │────────────────┐ │ (Write) │ │ └─────────────┘ │ ▼ ┌─────────────┐ │ Replica 1 │ │ (Read) │ └─────────────┘ ▼ ┌─────────────┐ │ Replica 2 │ │ (Analytics)│ └─────────────┘

### Architecture
1. **Primary database**: Handles all writes and critical reads
2. **Read Replica 1**: Serves user-facing read queries
3. **Read Replica 2**: Dedicated to analytics/reporting

### Routing Strategy
```typescript
const db = {
  primary: primaryConnection,
  read: replicaConnection,
  analytics: analyticsConnection,
};