CPU profiling
- Node.js course
- Advanced
- Lesson 16/83
- 5 min
Learn CPU profiling and flame graphs.
CPU profiling
CPU profiling finds which functions consume your app's time. Node.js uses the V8 engine's built-in profiler. There are two paths: start with the --cpu-prof flag, or use the inspector module to profile at runtime.
The inspector module gives access to the Chrome DevTools Protocol. You open a session with new Session(), start the profiler, stop it, and read the result. This is a powerful tool for finding bottlenecks in production.
PerformanceObserver
PerformanceObserver is a class in the perf_hooks module. It catches performance entries (PerformanceEntry) live. You create it with new PerformanceObserver(cb) and start it with .observe().
For example you place performance.mark("start") and performance.mark("end"), then measure the gap with performance.measure("label", "start", "end"). The observer catches these measurements and passes them to the callback. This is a declarative, W3C-standard measurement method.
Practice Log the type of PerformanceObserver
Import PerformanceObserver from perf_hooks. Log typeof PerformanceObserver.
Starter code
// import the module, get the observer
// log its typeSample solution
const { PerformanceObserver } = require("perf_hooks");
console.log(typeof PerformanceObserver);Expected output
function
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Which built-in module is used for CPU profiling?
- fs
- url
- path
- inspector Correct answer
Explanation: The inspector module gives access to the Chrome DevTools Protocol.
2 Match each piece to its role
| Term | Meaning |
|---|---|
inspector |
Profiling |
Session |
Connection |
PerformanceObserver |
Catches entries |
profiler |
CPU profile |
3 Complete the module name
const { Session } = require("____")const { Session } = require("inspector")Explanation: The inspector module loads as 'inspector'.