DB Migrations
Why Migrations?
Without: Dev adds column locally, breaks prod
With: V1 create table, V2 add column -> consistent
Tools
| Tool | Format |
|---|---|
| Flyway | SQL only |
| Liquibase | XML/YAML/SQL |
Best Practices
- Never modify applied migrations
- One change per file
- Test on production data copy
- Back up before production
- Version control migration files
Key Points
- Understanding Database Migrations is essential for production systems
- Always consider scalability and maintainability
- Test thoroughly before deploying to production
- Monitor performance and set up alerting
Common Patterns
- Validation: Always validate input at the boundary
- Error Handling: Use structured error responses
- Logging: Log key events for debugging
- Testing: Unit, integration, and load tests
- Documentation: Keep docs updated with code changes
Database Best Practices
Design Principles
- Normalize to 3NF, denormalize for performance
- Use appropriate data types
- Add indexes for frequent queries
- Implement proper constraints
Query Optimization
- Use EXPLAIN ANALYZE
- Avoid SELECT *
- Use JOIN instead of subqueries
- Implement pagination
Operations
- Regular backups
- Monitor slow queries
- Implement connection pooling
- Use read replicas for scaling
Key Points
- Understanding Database Migrations is essential for production systems
- Always consider scalability and maintainability
- Test thoroughly before deploying to production
- Monitor performance and set up alerting
Common Patterns
- Validation: Always validate input at the boundary
- Error Handling: Use structured error responses
- Logging: Log key events for debugging
- Testing: Unit, integration, and load tests
- Documentation: Keep docs updated with code changes
Practice Problems
Design and implement a solution for Database Migrations in a backend system. Consider scalability, error handling, and production readiness.
Solution
// Database Migrations implementation
// Key aspects: validation, error handling, logging, testing
public class DatabaseMigrations {
// Production-ready implementation
}Identify and handle edge cases for Database Migrations. What happens under high load, with invalid input, or during failures?
Solution
// Edge case handling:
// 1. Null/empty input -> validation
// 2. High load -> rate limiting, queuing
// 3. Failures -> retries, circuit breaker
// 4. Concurrent access -> locks, idempotencyWrite a testing strategy for Database Migrations. Include unit tests, integration tests, and performance tests.
Solution
// Test plan:
// - Unit: 80% coverage target
// - Integration: API contracts
// - Performance: latency, throughput
// - Chaos: failure injectionQuiz
1. Never modify applied migrations because?
2. Flyway naming?
3. What is the primary purpose of Database Migrations?
4. What is a common mistake when implementing Database Migrations?
Flashcards
Question
Migrations purpose?
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Answer
Version-control schema changes
Question
Flyway naming?
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Answer
V1__description.sql
Question
What is Database Migrations?
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Answer
Database Migrations is a key concept in backend development.
Question
When to use Database Migrations?
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Answer
Use Database Migrations when building production systems that require reliability, scalability, and maintainability.
Question
Database Migrations best practices
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Answer
Follow SOLID principles, write clean code, test thoroughly, document decisions, and monitor in production.
Revision Notes
Key Takeaways
- 1.Migrations version-control schema
- 2.Never modify applied migrations
- 3.One change per file
Interview Tips
- •Explain why migrations matter
- •Know Flyway vs Liquibase
Cheat Sheet
DB Migrations
- Version-control schema
- Never modify applied migrations
- Flyway: V1__name.sql
- Liquibase: changelog.xml