Database migrations are among the most critical and risky operations in software engineering. A botched migration can mean data loss, extended downtime, and unhappy users. This guide covers the best practices we have refined across thousands of migrations.
Planning Phase
- Audit your data: Know your schema size, row counts, index sizes, and data types before starting
- Map type differences: MySQL's TINYINT, PostgreSQL's BOOLEAN, and SQL Server's BIT are not equivalent
- Identify dependencies: Foreign keys, triggers, stored procedures, and views all need migration planning
- Set a maintenance window: Communicate downtime expectations to stakeholders
Execution Phase
- Always run a test migration on a staging environment first
- Use checksums to verify data integrity after migration
- Keep the source database read-only during final migration
- Have a documented rollback plan before starting
Post-Migration
- Verify row counts match between source and target
- Run application test suites against the new database
- Monitor query performance for the first 48 hours
- Keep the source database available for 2 weeks as a safety net