Add Flame Graphs to your Phoenix Application or LiveDashboard

For more information on flame graphs and an introduction to Flame On, see the announcement blog post

Add :flame_on to your dependencies:

def deps do
  [
    {:flame_on, "~> 0.7.0"}
  ]
end

And then add Flame On as a LiveDashboard page or a LiveComponent in your LiveView page

Modify the live_dashboard call in your Router:

live_dashboard "/dashboard",
  metrics: MyAppWeb.Telemetry,
  additional_pages: [
    flame_on: FlameOn.DashboardPage
  ]

You will now find a Flame On tab along the top of the LiveDashboard page

<.live_component module={FlameOn.Component} id="flame_on" width="100%" height="100%" />

Choose the Module, Function, and Arity of the function you want to profile, click "Flame On", and then trigger the function (e.g. make a web request in a new tab). Note that for Elixir modules, you will need to prefix them with Elixir, e.g. Elixir.Phoenix.Controller, while Erlang modules take simply the erlang module name, e.g. cowboy_handler. The default values of Bandit.Pipeline/run/4 (for newer Phoenix apps) and cowboy_handler/execute/2 (for older Phoenix apps) are the best way to capture a standard Phoenix Controller DeadView request or the DeadView request that kicks off a LiveView request.

Clicking a block will zoom the flamegraph to that block and recalculate the percents for the blocks such that the clicked block is now 100%. You can return to a higher level block by clicking the link for it above the blocks.

Flame On should not be run in critical production environments. Flame On uses :meck under the hood. This swaps out beam code paths and injects mock code that includes tracing. If you do need to use Flame On in a critical production node to diagnose a specific issue, I recommend rebuilding or restarting that node after running it.

:meck swaps out code paths and therefore you will need to include the beam files in your release. By default these are stripped, so in your release definition in mix.exs add the strip_beams: false flag:

releases: [
  my_app_web: [
    ...
    strip_beams: false
  ],

You may also need to explicitly include :meck as a dependency if it can't find it when trying to run in a release.

Credit to eFlambe for being the original capture engine used by Flame On and the inspiration for the current capture engine.

• Mike Binns

We are very thankful for the many contributors

This library follows Semantic Versioning

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