PlanetScale: AI-Optimized Technical Reference

Technology Overview

Core Platform: Managed MySQL database built on Vitess (Google's open-source MySQL scaling solution used by YouTube)

Key Value Proposition: Horizontal MySQL scaling with zero-downtime schema changes through database branching

Critical Warning: Vitess != Standard MySQL - missing foreign keys, triggers, stored procedures, FULLTEXT indexes

Configuration & Production Settings

Architecture Components

• VTGate (Query Router): Application interface, appears as standard MySQL, routes queries to appropriate shards
• VTTablet (Connection Manager): Handles connection pooling (thousands vs MySQL's 151 default limit)
• MySQL Instances: Standard MySQL servers (1 primary + 2 replicas per shard)

Automatic Failover

• Primary server failure triggers automatic replica promotion
• VTGate routes around failed servers without application changes
• Recovery Time: Typically seconds, not minutes

Performance Thresholds

• Connection Limits: ~151 standard MySQL vs thousands with VTTablet pooling
• UI Breaking Point: 1000+ spans make debugging distributed transactions impossible
• Query Cost Example: COUNT(*) on 800k table = $12, analytics query on 10M rows = $200

Critical Failure Modes & Workarounds

Database Branching Limitations

• Schema Only: Branches copy schema, not data - testing data-dependent migrations impossible
• Rollback Restrictions: Cannot undo destructive changes (column drops with data)
• Migration Dependencies: Subtle breaks only surface with production data

MySQL Compatibility Gaps

Missing Features That Break Applications:

• Foreign key constraints (referential integrity must move to application)
• Database triggers (business logic must be reimplemented)
• Stored procedures (rewrite in application language)
• FULLTEXT search (requires external search engine)

Real Impact Example: Order validation logic required 2-week rewrite when foreign keys weren't enforced, resulting in invalid orders reaching production

Pricing Shock Scenarios

Row-Based Billing Gotchas:

• SELECT * queries on wide tables compound costs exponentially
• Background ETL jobs: daily processing = $150/month
• Analytics queries: 10M row scan = $200 charge
• ORM inefficiency: Active Record's default behavior increases costs 3-5x

API Dependency Risk

• Schema deployment failures during API outages (3+ hour delays documented)
• Loss of branching functionality when API unavailable
• Mitigation: Avoid Friday deployments, have rollback plan ready

Resource Requirements & Timelines

Migration Complexity

Simple Applications (basic CRUD):

• Time Investment: 2-4 hours
• Difficulty: Low
• Breaking Changes: Minimal

Complex Applications (database-heavy features):

• Time Investment: 2-4 weeks
• Difficulty: High
• Breaking Changes: Foreign key removal, trigger rewrites, stored procedure migration
• Real Example: 3 days removing foreign key constraints due to ORM compatibility issues

Expertise Requirements

• Database Administration: Eliminated (managed service)
• Application Development: Increased (database logic moves to app layer)
• DevOps Complexity: Reduced (automatic scaling, backups)

Sharding Key Selection

• Critical Decision: Cannot change after implementation
• Failure Mode: Poor distribution (80% data on single shard documented)
• Planning Required: Analyze data distribution patterns before migration

Cost Decision Matrix

When PlanetScale is Cost-Effective

• Startup Phase: Permanent free tier vs AWS 12-month limit
• Rapid Scaling: Eliminates database admin overhead
• Schema-Heavy Development: Branching saves coordination time (20+ hours documented)

When Traditional MySQL is Cheaper

• Read-Heavy Workloads: Row-based pricing penalizes large scans
• Analytics Applications: Query costs can exceed server costs
• Stable Applications: If not using branching features, paying premium for unused functionality

Break-Even Analysis

• Connection Pooling Value: Significant for high-concurrency applications
• Branching Value: ~$50-100/hour saved in coordination time
• Scaling Value: Eliminates 3am emergency scaling scenarios

Implementation Warnings

Production Readiness Checklist

1. Remove Foreign Keys: Application must handle referential integrity
2. Test Sharding Key: Verify even data distribution with production-like data
3. Migrate Triggers: Reimplement business logic in application code
4. Update Stored Procedures: Convert to application-level functions
5. Plan Query Optimization: Row-based pricing requires efficient queries

Framework-Specific Issues

• Rails ActiveRecord: Foreign key warnings, ORM assumptions break
• Django ORM: Referential integrity moves to Python validation
• Laravel Eloquent: Relationships work but without database enforcement

Monitoring Requirements

• Query Performance: Use built-in insights for slow query identification
• Cost Monitoring: Track row reads/writes to prevent billing surprises
• Connection Pool Status: Monitor VTTablet connection limits

Decision Support Information

PlanetScale vs Alternatives

Scenario	Recommendation	Reasoning
Startup MVP	PlanetScale	Permanent free tier, zero ops overhead
High-Growth B2B	PlanetScale	Branching saves development velocity
Analytics Workload	Traditional MySQL/PostgreSQL	Row-based pricing prohibitive
Complex Database Logic	PostgreSQL on RDS	Foreign keys, triggers, stored procedures required
Cost-Sensitive	AWS RDS MySQL	Predictable instance-based pricing

Migration Risk Assessment

• Low Risk: Simple CRUD applications without foreign keys
• Medium Risk: Applications with moderate database constraints
• High Risk: Applications dependent on triggers, stored procedures, or complex referential integrity

Vendor Lock-in Mitigation

• Data Export: Standard mysqldump compatibility maintained
• Application Changes: Foreign key logic must be preserved for future migrations
• Workflow Dependencies: Branching/deployment automation requires rebuilding

Support & Community Quality

• Documentation Quality: Above average, technical accuracy high
• Community Response: Active Discord, PlanetScale team responsive
• Enterprise Support: Standard SLAs, compliance certifications (SOC 2, PCI DSS, HIPAA)

Critical Success Factors

1. Understanding Vitess Limitations before migration
2. Proper Sharding Key Selection (cannot be changed)
3. Query Optimization for row-based pricing model
4. Application Logic Migration for database constraints
5. Cost Monitoring setup from day one