# Database Migration Safety Guidelines

## Principles

1. **Additive changes only**: Production migrations should only add new columns, tables, or indexes
2. **No destructive changes**: Never DROP columns or tables in production migrations
3. **Two-phase migrations**: For destructive changes, use a two-phase approach:
   - Phase 1: Add new schema, deploy code to use it
   - Phase 2: Remove old schema after code is stable

## Migration Process

### Before Migration
1. Test migration on staging database
2. Verify application works with new schema
3. Take database backup
4. Document rollback procedure

### During Migration
1. Run migration in dry-run mode first
2. Apply migration to production
3. Verify migration completed successfully
4. Monitor application for errors

### After Migration
1. Verify all queries work correctly
2. Monitor performance metrics
3. Update documentation if needed

## Rollback Procedures

### Emergency Rollback
1. Stop application deployment
2. Restore database from backup
3. Revert to previous application version
4. Verify application functionality

### Planned Rollback
1. Deploy previous application version
2. Run rollback migration
3. Verify application functionality
4. Update monitoring dashboards

## Migration Checklist

- [ ] Migration tested on staging
- [ ] Backup taken before production migration
- [ ] Rollback procedure documented
- [ ] Team notified of maintenance window
- [ ] Monitoring dashboards prepared
- [ ] Support team on standby