Database migrations are risky. A bad migration can cause downtime or data loss. Here's how to migrate safely with zero downtime.
Migration Principles
Safe Migrations:
- Backward compatible
- Reversible
- Tested in staging
- Monitored during rollout
Dangerous Operations:
- Dropping columns/tables
- Renaming columns
- Changing column types
- Adding NOT NULL constraints
Adding Columns Safely
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Removing Columns (Expand/Contract Pattern)
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Renaming Columns
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Changing Column Types
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Adding Indexes Without Locking
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Large Table Migrations
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Prisma Migration Workflow
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Rollback Strategy
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Testing Migrations
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Best Practices
Planning:
✓ Review migrations before applying
✓ Test in staging first
✓ Have rollback plan ready
✓ Schedule during low-traffic periods
Execution:
✓ Use non-blocking operations
✓ Migrate data in batches
✓ Monitor database load
✓ Keep migrations small
Safety:
✓ Never drop columns immediately
✓ Use expand/contract pattern
✓ Backfill before constraints
✓ Verify data integrity
Conclusion
Safe database migrations require planning and patience. Use the expand/contract pattern, migrate data in batches, and always have a rollback plan. Test migrations thoroughly before production and monitor during execution.