init

.opencode/skills/sequential-thinking/references/examples-debug.md

@@ -0,0 +1,90 @@
+# Example: Performance Debugging with Sequential Thinking
+
+**Problem**: API endpoint slow (2-3s instead of <200ms).
+
+## Sequential Thinking Approach
+
+```
+Thought 1/5: Initial investigation
+
+Endpoint: GET /api/users/{id}/dashboard
+Expected: <200ms
+Actual: 2-3s
+
+Need to identify bottleneck.
+Next: Analyze endpoint logic
+
+Thought 2/5: Endpoint analysis
+
+Dashboard fetches:
+- User profile
+- Recent activities (last 50)
+- Notifications (unread)
+- Analytics summary
+
+Each is separate DB query. Could be N+1 problem.
+Next: Profile actual execution
+
+Thought 3/6: Profiling results (adjusted up—more complex)
+
+Profiling:
+- User profile: 20ms
+- Activities: 1800ms (!!)
+- Notifications: 100ms
+- Analytics: 80ms
+
+Activities query is bottleneck (90% of time).
+Need to examine that query.
+Next: Investigate activities query
+
+Thought 4/6 [BRANCH A]: Hypothesis - N+1 query
+
+Activities table has user_id FK to users.
+Query might fetch activities, then user for each (N+1).
+Verification: Check if uses joins or loops.
+
+Thought 4/6 [BRANCH B]: Hypothesis - Missing index
+
+Activities table might lack index on user_id + created_at.
+Without index, full table scan for user's activities.
+Verification: Check table indexes.
+
+Thought 5/6 [VERIFICATION]: Testing hypotheses
+
+Query examination: Uses proper joins (not N+1).
+Index check: user_id indexed, NOT created_at.
+Query filters by user_id AND sorts by created_at.
+
+Branch B confirmed: Missing composite index causes slow sort.
+Branch A eliminated: No N+1 issue.
+
+Root cause identified.
+Next: Implement solution
+
+Thought 6/6 [FINAL]: Solution and verification
+
+Create composite index:
+```sql
+CREATE INDEX idx_activities_user_created
+ON activities(user_id, created_at DESC);
+```
+
+Tested: Response time now 120ms (target met).
+
+Confidence: High (verified with profiling)
+Result: 95% performance improvement
+```
+
+## Key Techniques Demonstrated
+
+1. **Branching for hypothesis testing**: Explored N+1 vs index hypotheses in parallel
+2. **Verification before solution**: Tested both hypotheses systematically
+3. **Data-driven decisions**: Used profiling data to guide investigation
+4. **Dynamic adjustment**: Expanded thought count when complexity emerged
+5. **Elimination method**: Ruled out N+1, confirmed index issue
+
+## Comparison
+
+**Without sequential thinking**: Might jump to N+1 conclusion (common issue), waste time optimizing wrong thing.
+
+**With sequential thinking**: Systematically tested hypotheses, identified actual root cause, implemented correct fix.