# TiDB Migration - Detailed Planning

**Author**: Sarah Chen
**Date**: 2025-01-14
**Status**: Planning
**Stakeholders**: Engineering, DevOps, Product

## Executive Summary
Migrating from PostgreSQL 14 to TiDB 8.0 to support horizontal scaling and reduce operational complexity. TiDB provides MySQL compatibility with automatic sharding.

## Current Pain Points
1. **Scaling bottleneck**: Single PostgreSQL instance hitting 80% CPU during peak hours
2. **Read replicas**: Manual failover process, replication lag issues
3. **Sharding complexity**: Application-level sharding is brittle
4. **Cost**: RDS costs growing 40% YoY

## TiDB Benefits
- **Horizontal scalability**: Add TiKV nodes without downtime
- **Strong consistency**: No eventual consistency problems
- **MySQL protocol**: Most PostgreSQL queries compatible
- **Cloud-native**: Runs on Kubernetes (our existing EKS cluster)
- **Cost**: 30% reduction vs RDS PostgreSQL at target scale

## Migration Strategy

### Phase 1: POC (2 weeks)
- Deploy TiDB cluster in staging
- Migrate 3 non-critical tables
- Run dual-writes for 1 week
- Validate query performance

### Phase 2: Pilot (4 weeks)
- Migrate analytics workload (20% of traffic)
- Monitor performance metrics
- Build confidence with ops team

### Phase 3: Full Migration (8 weeks)
- Migrate remaining tables in batches
- Blue-green deployment strategy
- Rollback plan at each step

## Technical Considerations

### SQL Compatibility
```sql
-- PostgreSQL SERIAL → TiDB AUTO_INCREMENT
-- PostgreSQL JSONB → TiDB JSON (fully compatible)
-- PostgreSQL array types → Requires schema change
```

### Performance Tuning
- TiDB optimized for OLTP workloads
- May need to adjust indexes for distributed architecture
- Monitor PD (Placement Driver) metrics closely

## Risk Mitigation
- **Data loss**: Continuous backup to S3 during migration
- **Downtime**: Blue-green deployment keeps old cluster running
- **Performance regression**: Load testing before each phase
- **Team knowledge**: TiDB training sessions, documentation

## Timeline
- Week 1-2: POC
- Week 3-6: Pilot
- Week 7-14: Full migration
- Week 15-16: Optimization and cleanup

## Related Documents
- TiDB Architecture Deep Dive (internal wiki)
- Cost Analysis Spreadsheet (Confluence)
- EKS Cluster Capacity Planning (Jira)
