Performance Engineering System From "it's slow" to "here's why and here's the fix" — a complete methodology for measuring, diagnosing, optimizing, and preventing performance problems. Phase 1: Performance Investigation Brief Before touching anything, define the problem. Performance Budget Framework Set budgets BEFORE building, not after complaints: | Metric | Web App | API | Mobile | Batch Job | |--------|---------|-----|--------|-----------| | P50 response | <200ms | <100ms | <300ms | N/A | | P95 response | <500ms | <250ms | <800ms | N/A | | P99 response | <1s | <500ms | <1.5s | N/A | | Erro…