How to use pprof in Go program

How to use pprof in Go program?

There is a Go package named net/http/pprof,but I can't use it.

The document says go tool pprof http://localhost:6060/debug/pprof/heap ,which does not work.

And,what does the below _ mean?

import _ "net/http/pprof"

Based on your comment, the issue might be that you're not using the correct port number.

If you are running an http server at http://localhost:9997, then I think you want to run the command with http://localhost:9997:

$ go tool pprof http://localhost:9997/debug/pprof/heap

According to the net/http/pprof pkg doc page, if your application is already running an http server you do not need to start one and only need to include the import _ "net/http/pprof" somewhere in your program. http://localhost:6060 is the server started as an example and the host and port are arbitrary.

import _ "net/http/pprof" means the package is imported but you do not use any of its exported identifiers. According to the go language spec, this will import the package solely for its side effects. These side effects involve, I think, the execution of the init() functions defined in the package's source files and, apparently, registered variables.

Also, you might find this blog post helpful:

http://blog.golang.org/2011/06/profiling-go-programs.html

What "does not work" means? What is expected and what is observed instead?

Run

$ go tool pprof -h

to see help for your version of this tool. My local version is not at tip neither at release (ie. in between). It shows:

(10:16) jnml@fsc-r550:~$ go tool pprof -h
Option h is ambiguous (heapcheck, help)
Invalid option(s)

Usage:
pprof [options] <program> <profiles>
   <profiles> is a space separated list of profile names.
pprof [options] <symbolized-profiles>
   <symbolized-profiles> is a list of profile files where each file contains
   the necessary symbol mappings  as well as profile data (likely generated
   with --raw).
pprof [options] <profile>
   <profile> is a remote form.  Symbols are obtained from host:port/pprof/symbol

   Each name can be:
   /path/to/profile        - a path to a profile file
   host:port[/<service>]   - a location of a service to get profile from

   The /<service> can be /pprof/heap, /pprof/profile, /pprof/pmuprofile,
                         /pprof/growth, /pprof/contention, /pprof/wall,
                         /pprof/thread, or /pprof/filteredprofile.
   For instance:
     pprof http://myserver.com:80/pprof/heap
   If /<service> is omitted, the service defaults to /pprof/profile (cpu profiling).
pprof --symbols <program>
   Maps addresses to symbol names.  In this mode, stdin should be a
   list of library mappings, in the same format as is found in the heap-
   and cpu-profile files (this loosely matches that of /proc/self/maps
   on linux), followed by a list of hex addresses to map, one per line.

   For more help with querying remote servers, including how to add the
   necessary server-side support code, see this filename (or one like it):

   /usr/doc/google-perftools-1.5/pprof_remote_servers.html

Options:
   --cum               Sort by cumulative data
   --base=<base>       Subtract <base> from <profile> before display
   --interactive       Run in interactive mode (interactive "help" gives help) [default]
   --seconds=<n>       Length of time for dynamic profiles [default=30 secs]
   --add_lib=<file>    Read additional symbols and line info from the given library
   --lib_prefix=<dir>  Comma separated list of library path prefixes

Reporting Granularity:
   --addresses         Report at address level
   --lines             Report at source line level
   --functions         Report at function level [default]
   --files             Report at source file level

Output type:
   --text              Generate text report
   --callgrind         Generate callgrind format to stdout
   --gv                Generate Postscript and display
   --web               Generate SVG and display
   --list=<regexp>     Generate source listing of matching routines
   --disasm=<regexp>   Generate disassembly of matching routines
   --symbols           Print demangled symbol names found at given addresses
   --dot               Generate DOT file to stdout
   --ps                Generate Postcript to stdout
   --pdf               Generate PDF to stdout
   --svg               Generate SVG to stdout
   --gif               Generate GIF to stdout
   --raw               Generate symbolized pprof data (useful with remote fetch)

Heap-Profile Options:
   --inuse_space       Display in-use (mega)bytes [default]
   --inuse_objects     Display in-use objects
   --alloc_space       Display allocated (mega)bytes
   --alloc_objects     Display allocated objects
   --show_bytes        Display space in bytes
   --drop_negative     Ignore negative differences

Contention-profile options:
   --total_delay       Display total delay at each region [default]
   --contentions       Display number of delays at each region
   --mean_delay        Display mean delay at each region

Call-graph Options:
   --nodecount=<n>     Show at most so many nodes [default=80]
   --nodefraction=<f>  Hide nodes below <f>*total [default=.005]
   --edgefraction=<f>  Hide edges below <f>*total [default=.001]
   --focus=<regexp>    Focus on nodes matching <regexp>
   --ignore=<regexp>   Ignore nodes matching <regexp>
   --scale=<n>         Set GV scaling [default=0]
   --heapcheck         Make nodes with non-0 object counts
                       (i.e. direct leak generators) more visible

Miscellaneous:
   --tools=<prefix>    Prefix for object tool pathnames
   --test              Run unit tests
   --help              This message
   --version           Version information

Environment Variables:
   PPROF_TMPDIR        Profiles directory. Defaults to $HOME/pprof
   PPROF_TOOLS         Prefix for object tools pathnames

Examples:

pprof /bin/ls ls.prof
                       Enters "interactive" mode
pprof --text /bin/ls ls.prof
                       Outputs one line per procedure
pprof --web /bin/ls ls.prof
                       Displays annotated call-graph in web browser
pprof --gv /bin/ls ls.prof
                       Displays annotated call-graph via 'gv'
pprof --gv --focus=Mutex /bin/ls ls.prof
                       Restricts to code paths including a .*Mutex.* entry
pprof --gv --focus=Mutex --ignore=string /bin/ls ls.prof
                       Code paths including Mutex but not string
pprof --list=getdir /bin/ls ls.prof
                       (Per-line) annotated source listing for getdir()
pprof --disasm=getdir /bin/ls ls.prof
                       (Per-PC) annotated disassembly for getdir()

pprof http://localhost:1234/
                       Enters "interactive" mode
pprof --text localhost:1234
                       Outputs one line per procedure for localhost:1234
pprof --raw localhost:1234 > ./local.raw
pprof --text ./local.raw
                       Fetches a remote profile for later analysis and then
                       analyzes it in text mode.

FATAL ERROR: Invalid option(s)
go tool pprof: exit status 1
(10:16) jnml@fsc-r550:~$ 

On the second question: The `import _ "foo"' idiom is importing package foo only for the side effects of foo's initialization. That may include for example registering functionality provided by foo to be usable from within other packages. A concrete example for this are the specific image format handling packages (see bottom at"Subdirectories") and the abstract image package.