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intermediate Phase · Database Integration

Database Migrations

Manage database schema changes with version-controlled migrations.

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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

  1. Never modify applied migrations
  2. One change per file
  3. Test on production data copy
  4. Back up before production
  5. 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

  1. Validation: Always validate input at the boundary
  2. Error Handling: Use structured error responses
  3. Logging: Log key events for debugging
  4. Testing: Unit, integration, and load tests
  5. 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

  1. Validation: Always validate input at the boundary
  2. Error Handling: Use structured error responses
  3. Logging: Log key events for debugging
  4. Testing: Unit, integration, and load tests
  5. Documentation: Keep docs updated with code changes

Practice Problems

0 / 3 solved
Implement Database Migrations

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
}
Database Migrations Edge Cases

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, idempotency
Database Migrations Testing Strategy

Write 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 injection

Quiz

1. Never modify applied migrations because?

Question 1 options

2. Flyway naming?

Question 2 options

3. What is a common mistake when implementing Database Migrations?

Question 3 options

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

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