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intermediate Phase · Database Integration

Connection Pooling

Understand why connection pooling is essential and how it works.

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Connection Pooling

Why Connection Pooling?

Without pool: Create → Use → Close (slow)
With pool: Borrow → Use → Return (fast)

HikariCP Configuration (Spring Boot Default)

spring:
  datasource:
    hikari:
      maximum-pool-size: 20
      minimum-idle: 5
      idle-timeout: 300000
      connection-timeout: 20000

Pool Parameters

Parameter Description Recommended
max-pool-size Max connections 20-30 per core
min-idle Min idle connections 5-10
idle-timeout Idle before closing 5-10 min

Best Practices

Key Principles

  1. Follow SOLID principles
  2. Write clean, readable code
  3. Test thoroughly
  4. Document decisions
  5. Monitor in production

Implementation

  • Start simple, refactor as needed
  • Use established patterns
  • Consider trade-offs
  • Review with peers

Continuous Improvement

  • Learn from incidents
  • Update documentation
  • Share knowledge
  • Mentor others

Key Points

  • Understanding Connection Pooling 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 Connection Pooling

Design and implement a solution for Connection Pooling in a backend system. Consider scalability, error handling, and production readiness.

Solution 
// Connection Pooling implementation
// Key aspects: validation, error handling, logging, testing

public class ConnectionPooling {
    // Production-ready implementation
}
Connection Pooling Edge Cases

Identify and handle edge cases for Connection Pooling. 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
Connection Pooling Testing Strategy

Write a testing strategy for Connection Pooling. 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. Default connection pool in Spring Boot?

Question 1 options

2. What happens when all connections are busy?

Question 2 options

3. What is a common mistake when implementing Connection Pooling?

Question 3 options

Flashcards

Question

Default Spring Boot pool?

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Answer

HikariCP

Question

Max pool size?

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Answer

20-30 per CPU core

Question

Connection Pooling 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. HikariCP is Spring Boot default
  • 2. Configure max-pool-size, min-idle, timeouts
  • 3. Monitor pool metrics

Interview Tips

  • • Know pool configuration
  • • Explain why pooling matters

Cheat Sheet

Connection Pooling

  • Default: HikariCP
  • max-pool-size: 20-30 per core
  • Monitor: active, idle, waiting