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Log Levels

Use ERROR, WARN, INFO, DEBUG, and TRACE appropriately.

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Log Levels

When to Use Each

Level When
ERROR Something broke, needs attention
WARN Potential issue, not critical
INFO Key business events
DEBUG Detailed diagnostic info
TRACE Very detailed, method-level

Key Points

  • Understanding Log Levels 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

Logging Best Practices

Levels

TRACE < DEBUG < INFO < WARN < ERROR < FATAL

Structured Logging

{
  "timestamp": "...",
  "level": "INFO",
  "message": "...",
  "requestId": "..."
}

Best Practices

  • Use SLF4J facade
  • Include correlation IDs
  • Don't log sensitive data
  • Use appropriate levels

Key Points

  • Understanding Log Levels 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

0/3solved
Implement Log Levels

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

Solution
// Log Levels implementation
// Key aspects: validation, error handling, logging, testing

public class LogLevels {
    // Production-ready implementation
}
Log Levels Edge Cases

Identify and handle edge cases for Log Levels. 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
Log Levels Testing Strategy

Write a testing strategy for Log Levels. 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. Use ERROR level for?

Question 1 options

2. Production default level?

Question 2 options

3. What is the primary purpose of Log Levels?

Question 3 options

4. What is a common mistake when implementing Log Levels?

Question 4 options

Flashcards

Question

ERROR level use?

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Answer

Something broke, needs attention

Question

Production level?

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Answer

INFO (default)

Question

What is Log Levels?

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Answer

Log Levels is a key concept in backend development.

Question

When to use Log Levels?

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Answer

Use Log Levels when building production systems that require reliability, scalability, and maintainability.

Question

Log Levels 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.ERROR: broken, needs attention
  • 2.WARN: potential issue
  • 3.INFO: business events
  • 4.DEBUG: diagnostics
  • 5.TRACE: very detailed

Interview Tips

  • •Choose correct log levels
  • •Configure per-package

Cheat Sheet

Log Levels

  • ERROR: broken, needs attention
  • WARN: potential issue
  • INFO: business events
  • DEBUG: diagnostics
  • TRACE: very detailed
  • Production: INFO