read_book/.trae/skills/debugging/references/debugging-workflows.md

author, status, updated, version, tag, type, parent

author	status	updated	version	tag	type	parent
Joseph OBrien	unpublished	2025-12-23	1.0.1	skill	reference	debugging

Debugging Workflows

Reference guide for common debugging workflows and techniques across different scenarios.

Debugging Workflows by Issue Type

Production Errors

Workflow:

1. Capture error message and stack trace
2. Check error logs for context
3. Identify when error started (deployment, traffic spike, etc.)
4. Reproduce in staging environment
5. Add logging to trace execution path
6. Identify root cause
7. Implement fix with tests
8. Deploy and monitor

Tools:

• Error tracking (Sentry, Rollbar)
• Log aggregation (ELK, Datadog)
• APM tools (New Relic, AppDynamics)

Test Failures

Workflow:

1. Read test failure message
2. Understand what the test expects
3. Run test in isolation
4. Check test data and setup
5. Trace through code execution
6. Identify why test fails
7. Fix code or test as appropriate
8. Verify test passes

Tools:

• Test runner debug mode
• IDE debugger
• Test coverage tools

Performance Issues

Workflow:

1. Measure current performance
2. Identify slow operations
3. Profile to find bottlenecks
4. Analyze profiling data
5. Optimize identified bottlenecks
6. Measure improvement
7. Verify no regressions

Tools:

• Profilers (Chrome DevTools, py-spy)
• APM tools
• Performance monitoring

Language-Specific Debugging

JavaScript/Node.js

Debugging Tools:

• Chrome DevTools
• Node.js debugger
• console.log (strategic logging)
• debugger statement

Common Issues:

• Undefined variables
• Async/await errors
• Promise rejections
• Scope issues
• Type coercion

Techniques:

• Use debugger breakpoints
• Log variable states
• Check call stack
• Inspect closures
• Monitor event loop

Python

Debugging Tools:

• pdb (Python debugger)
• ipdb (enhanced debugger)
• print() statements
• logging module

Common Issues:

• AttributeError
• TypeError
• IndentationError
• Import errors
• NameError

Techniques:

• Use pdb.set_trace()
• Check variable types
• Verify imports
• Check indentation
• Use type hints

Java

Debugging Tools:

• IntelliJ debugger
• Eclipse debugger
• jdb (command line)
• Logging frameworks

Common Issues:

• NullPointerException
• ClassCastException
• OutOfMemoryError
• StackOverflowError

Techniques:

• Set breakpoints
• Inspect variables
• Check exception stack traces
• Monitor memory usage
• Use profilers

Debugging Techniques

Binary Search

When to Use:

• Large codebase
• Unclear where issue is
• Many potential causes

Process:

1. Divide code in half
2. Test which half has issue
3. Repeat on problematic half
4. Narrow down to specific location

Rubber Duck Debugging

Process:

1. Explain code to "rubber duck" (or yourself)
2. Walk through execution step by step
3. Identify assumptions
4. Find where logic breaks

Logging Strategy

What to Log:

• Function entry/exit
• Variable values at key points
• Decision points (if/else branches)
• Error conditions
• Performance metrics

Log Levels:

• DEBUG: Detailed diagnostic info
• INFO: General informational messages
• WARN: Warning messages
• ERROR: Error conditions
• CRITICAL: Critical failures

Reproducing Issues

Steps:

1. Identify exact conditions that trigger issue
2. Document steps to reproduce
3. Create minimal test case
4. Verify issue reproduces consistently
5. Isolate variables

Common Challenges:

• Intermittent issues
• Race conditions
• Environment-specific
• Data-dependent

Debugging Checklist

Before Starting

• Understand what should happen
• Understand what's actually happening
• Have reproduction steps
• Have access to logs/debugger

During Debugging

• Form hypotheses
• Test hypotheses systematically
• Document findings
• Check assumptions
• Look for patterns

After Finding Root Cause

• Verify root cause is correct
• Understand why it happened
• Implement fix
• Test fix thoroughly
• Check for similar issues
• Document solution

Common Error Patterns

Reference guide for identifying and resolving common error patterns across different systems and languages.

Database Errors

Connection Pool Exhaustion

Symptoms:

• ECONNREFUSED errors
• Errors spike during high traffic
• Connection pool size is smaller than concurrent requests

Pattern:

Error: ECONNREFUSED
Connection pool exhausted
Too many connections

Root Causes:

• Connection pool size too small
• Connections not being released
• Long-running transactions holding connections
• Missing connection cleanup in error handlers

Solutions:

• Increase connection pool size
• Ensure connections are released in finally blocks
• Add connection timeout
• Implement connection retry logic

N+1 Query Problem

Symptoms:

• Slow response times
• Many database queries for single operation
• Queries increase linearly with data size

Pattern:

SELECT * FROM users;
SELECT * FROM posts WHERE user_id = 1;
SELECT * FROM posts WHERE user_id = 2;
SELECT * FROM posts WHERE user_id = 3;
...

Solutions:

• Use eager loading (JOINs)
• Batch queries
• Use data loaders
• Implement query result caching

Memory Leaks

Event Listener Leaks

Symptoms:

• Memory usage grows over time
• No decrease after component/page unload
• Correlates with user interactions

Pattern:

// Problem: Listeners registered but never removed
window.addEventListener('resize', handler);
// Missing: window.removeEventListener('resize', handler);

Solutions:

• Always remove event listeners
• Use cleanup functions in React useEffect
• Use WeakMap for automatic cleanup
• Monitor listener count

Closure Leaks

Symptoms:

• Memory growth in long-running applications
• Large objects retained in closures
• Circular references

Pattern:

// Problem: Large object retained in closure
function createHandler(largeData) {
  return function() {
    // largeData retained even if not used
  };
}

Solutions:

• Avoid retaining large objects in closures
• Use WeakMap/WeakSet when possible
• Clear references when done
• Use memory profilers to identify leaks

Race Conditions

Concurrent Modification

Symptoms:

• Intermittent failures
• Data inconsistency
• Errors only under load

Pattern:

Thread 1: Read value (100)
Thread 2: Read value (100)
Thread 1: Write value (101)
Thread 2: Write value (101) // Lost update

Solutions:

• Use locks/mutexes
• Implement optimistic locking
• Use atomic operations
• Add request queuing

Async Race Conditions

Symptoms:

• Results arrive out of order
• Stale data displayed
• Race between multiple async operations

Pattern:

// Problem: Race between requests
fetch('/api/users/1').then(setUser1);
fetch('/api/users/2').then(setUser2);
// Results may arrive in wrong order

Solutions:

• Use Promise.all for parallel operations
• Cancel previous requests
• Use request IDs to match responses
• Implement request deduplication

Timeout Issues

Request Timeouts

Symptoms:

• Requests fail after specific duration
• Timeout errors in logs
• Slow external dependencies

Pattern:

Error: Request timeout after 30000ms
ETIMEDOUT

Solutions:

• Increase timeout for slow operations
• Implement retry with exponential backoff
• Add timeout configuration
• Optimize slow operations

Database Query Timeouts

Symptoms:

• Queries fail after timeout period
• Slow query logs show long-running queries
• Timeouts during peak load

Solutions:

• Optimize slow queries
• Add appropriate indexes
• Increase query timeout
• Implement query cancellation

Authentication Errors

Token Expiration

Symptoms:

• 401 Unauthorized errors
• Errors after specific time period
• Token refresh needed

Pattern:

401 Unauthorized
Token expired
Invalid token

Solutions:

• Implement token refresh logic
• Handle token expiration gracefully
• Add token expiration checks
• Use refresh tokens

Session Expiration

Symptoms:

• Users logged out unexpectedly
• Session errors after inactivity
• Cookie expiration issues

Solutions:

• Extend session on activity
• Implement session refresh
• Handle expiration gracefully
• Clear expired sessions

Network Errors

Connection Refused

Symptoms:

• Service unavailable errors
• Connection refused errors
• Service not running

Pattern:

ECONNREFUSED
Connection refused
Service unavailable

Solutions:

• Check if service is running
• Verify port configuration
• Check firewall rules
• Implement health checks

DNS Resolution Failures

Symptoms:

• Cannot resolve hostname
• DNS lookup failures
• Network configuration issues

Pattern:

ENOTFOUND
DNS resolution failed
getaddrinfo failed

Solutions:

• Verify DNS configuration
• Check hostname spelling
• Use IP addresses as fallback
• Implement DNS caching

Application Errors

Null Reference Errors

Symptoms:

• NullPointerException (Java)
• TypeError: Cannot read property (JavaScript)
• AttributeError (Python)

Pattern:

TypeError: Cannot read property 'x' of undefined
NullPointerException
AttributeError: 'NoneType' object has no attribute

Solutions:

• Add null checks
• Use optional chaining
• Provide default values
• Validate inputs

Type Errors

Symptoms:

• Type mismatch errors
• Invalid type errors
• Casting failures

Pattern:

TypeError: expected string, got number
InvalidCastException
Type mismatch

Solutions:

• Add type validation
• Use type guards
• Implement proper type checking
• Handle type conversions

Performance Errors

Out of Memory

Symptoms:

• Application crashes
• Memory limit exceeded
• Heap out of memory

Pattern:

OutOfMemoryError
Heap out of memory
Memory limit exceeded

Solutions:

• Increase memory limits
• Optimize memory usage
• Implement pagination
• Use streaming for large data

CPU Exhaustion

Symptoms:

• Slow response times
• High CPU usage
• Application freezing

Pattern:

• High CPU utilization (90%+)
• Slow processing
• Event loop blocking

Solutions:

• Optimize algorithms
• Use worker threads
• Implement caching
• Break up long-running tasks