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How do you profile CPU usage with --prof, 0x, or clinic.js flame graphs?

Q: How do you profile CPU usage with --prof, 0x, or clinic.js flame graphs?

**TL;DR.** Profile to find **hot functions** and **event-loop blockers**. node --prof writes a V8 tick log you process with --prof-process ; **0x** and **clinic.js flame** render **flame graphs** where **wide frames** are the functions burning the most CPU. They turn "it's slow" into a specific function to fix. main handleRequest parseBigJSON (hot) <text class='d-sub' x=

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Understand the problem

Finding hot functions and event-loop blockers.

nodejsperformanceprofilingflame-graph

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Read the code

Capture a flame graph

# 0x: wraps your app, opens an interactive flame graph
npx 0x -- node server.js          # generate load, then Ctrl-C

# clinic: diagnose first, then flame
npx clinic doctor -- node server.js
npx clinic flame  -- node server.js

# Dependency-free V8 profiler:
node --prof server.js && node --prof-process isolate-*.log > profile.txt

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