pprof

Documentation

Overview

Package pprof serves via its HTTP server runtime profiling data in the format expected by the pprof visualization tool.

The package is typically only imported for the side effect of registering its HTTP handlers. The handled paths all begin with /debug/pprof/.

To use pprof, link this package into your program:

import _ "net/http/pprof"

If your application is not already running an http server, you need to start one. Add "net/http" and "log" to your imports and the following code to your main function:

go func() {
	log.Println(http.ListenAndServe("localhost:6060", nil))
}()

By default, all the profiles listed in runtime/pprof.Profile are available (via Handler), in addition to the Cmdline, Profile, Symbol, and Trace profiles defined in this package. If you are not using DefaultServeMux, you will have to register handlers with the mux you are using.

Parameters

Parameters can be passed via GET query params:

• debug=N (all profiles): response format: N = 0: binary (default), N > 0: plaintext
• gc=N (heap profile): N > 0: run a garbage collection cycle before profiling
• seconds=N (allocs, block, goroutine, heap, mutex, threadcreate profiles): return a delta profile
• seconds=N (cpu (profile), trace profiles): profile for the given duration

Usage examples

Use the pprof tool to look at the heap profile:

go tool pprof http://localhost:6060/debug/pprof/heap

Or to look at a 30-second CPU profile:

go tool pprof http://localhost:6060/debug/pprof/profile?seconds=30

Or to look at the goroutine blocking profile, after calling runtime.SetBlockProfileRate in your program:

go tool pprof http://localhost:6060/debug/pprof/block

Or to look at the holders of contended mutexes, after calling runtime.SetMutexProfileFraction in your program:

go tool pprof http://localhost:6060/debug/pprof/mutex

The package also exports a handler that serves execution trace data for the "go tool trace" command. To collect a 5-second execution trace:

curl -o trace.out http://localhost:6060/debug/pprof/trace?seconds=5
go tool trace trace.out

To view all available profiles, open http://localhost:6060/debug/pprof/ in your browser.

For a study of the facility in action, visit https://blog.golang.org/2011/06/profiling-go-programs.html.

Index

• func Cmdline(w http.ResponseWriter, r *http.Request)
• func Handler(name string) http.Handler
• func Index(w http.ResponseWriter, r *http.Request)
• func Profile(w http.ResponseWriter, r *http.Request)
• func Symbol(w http.ResponseWriter, r *http.Request)
• func Trace(w http.ResponseWriter, r *http.Request)

Functions

func Cmdline

func Cmdline(w http.ResponseWriter, r *http.Request)

Cmdline responds with the running program's command line, with arguments separated by NUL bytes. The package initialization registers it as /debug/pprof/cmdline.

func Handler

func Handler(name string) http.Handler

Handler returns an HTTP handler that serves the named profile. Available profiles can be found in runtime/pprof.Profile.

func Index

func Index(w http.ResponseWriter, r *http.Request)

Index responds with the pprof-formatted profile named by the request. For example, "/debug/pprof/heap" serves the "heap" profile. Index responds to a request for "/debug/pprof/" with an HTML page listing the available profiles.

func Profile

func Profile(w http.ResponseWriter, r *http.Request)

Profile responds with the pprof-formatted cpu profile. Profiling lasts for duration specified in seconds GET parameter, or for 30 seconds if not specified. The package initialization registers it as /debug/pprof/profile.

func Symbol

func Symbol(w http.ResponseWriter, r *http.Request)

Symbol looks up the program counters listed in the request, responding with a table mapping program counters to function names. The package initialization registers it as /debug/pprof/symbol.

func Trace

func Trace(w http.ResponseWriter, r *http.Request)

Trace responds with the execution trace in binary form. Tracing lasts for duration specified in seconds GET parameter, or for 1 second if not specified. The package initialization registers it as /debug/pprof/trace.