What is pprof?

Learn the basics of the pprof profiling tool.

What is pprof?

pprof is Go's profiling tool that shows where a program spends its time and memory. It lets you measure instead of guess. It is added to an HTTP service with one line:

import _ "net/http/pprof"

go http.ListenAndServe("localhost:6060", nil)

Then go tool pprof http://localhost:6060/debug/pprof/profile?seconds=30 takes a 30-second CPU profile.

Profile types

There are several profiles under /debug/pprof/: profile (CPU), heap (memory), goroutine (all goroutine stacks), block and mutex (waiting points), allocs (all allocations). The goroutine profile is very handy for finding leaked goroutines.

Exercise Goroutine count

runtime.NumGoroutine() returns the number of running goroutines. Start three goroutines (each waiting on <-dur), print the count, then call close(dur).

Show example solution

package main

import (
    "fmt"
    "runtime"
)

func main() {
    dur := make(chan struct{})
    for i := 0; i < 3; i++ {
        go func() { <-dur }()
    }
    fmt.Println(runtime.NumGoroutine())
    close(dur)
}

Test yourself

Why bind the pprof endpoint to <code>localhost</code>?
- pprof doesn't work on other addresses
- To avoid port conflicts
- Profile data exposes internals; it shouldn't be public
- So it runs faster
Show answer

Profile data exposes internals; it shouldn't be public — Profiles reveal function names, stacks and hints about memory contents; taking a profile also loads the server.

Add pprof

import _ "net/http/____"

Show answer

import _ "net/http/pprof"

Profile and question

profile

Where is CPU spent?
heap

Where is memory held?
goroutine

Which goroutines exist?
mutex

Where is lock waiting?

Next lesson: CPU profiling

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies