Distillery staging release does not bundling :fprof

Questions / Help
1

Want to run fprof through a rpc

def profiler() do
    :fprof.trace([:start, verbose: true, procs: :all])
    spawn fn ->
      :timer.sleep(60_000)
      :fprof.trace(:stop)
      :fprof.profile()
      :fprof.analyse(totals: false, dest: 'textbook.analysis')
    end
  end

I thought by adding “set include_system_libs: true” to rel/config.exs would include the :fprof
But what I get is

PC to 'textbook@127.0.0.1' failed: {'EXIT',
                                     {undef,
                                      [{fprof,trace,
                                        [[start,{verbose,true},{procs,all}]],
                                        []},
                                       {'Elixir.Release.Tasks',profiler,0,
                                        [{file,
                                          "lib/textbook/release_tasks.ex"},
                                         {line,31}]},
                                       {rpc,'-handle_call_call/6-fun-0-',5,
                                        [{file,"rpc.erl"},{line,197}]}]}}

So sad

2

include_system_libs does include the ERTS AFAIK, so you do not need to install erlang at the host.
To actually get the :fprof application into your release, you have to add it under your (extra_)applications-key in mix.exs.

3

When I add :fprof to extra_application, my application does not start with error:

** (Mix) Could not start application fprof: could not find application file: fprof.app

I also can not use :fprof in my production system for profiling. But I am able to use :fprof in development, without adding :fprof to extrac_applications.

Elixir/Erlang version:

Erlang/OTP 20 [erts-9.0.1]
IEx 1.5.1

4

:fprof is part of erlangs :tools app, perhaps it helps to add that one.

In general, when you have installed erlang globally then you have this app usually available, but for a bundled release, it is a bit different. A bundled release can only see dependencies which are bundled. It will never use globally installed modules or applications (well, when not bundling ERTS then :stdlib and :kernel are used from the installed ERTS, but thats it). This is to ensure reproducability.

So, either find the correct application to bundle, or even better, do not profile on production. It will slow down your system drastically, dramatically increase its memory consumption and probably crash your BEAM.

1 Like
5

I’m aware of performance degration when profiling, but I need it to be on production, under load, to see what is causing high cpu usage.

The :tools app did work, thanks!