I recently noticed that Elixir’s Logger defaults its primary log level to :debug when no :logger, :level application configuration is present. In Logger.App, the default ultimately comes from this line : Application.get_env(:logger, :level, :debug) Would something like :info or even :warning be a …

Yes, it would be more reasonable default to use :info by default, but because of backward compatibility it needs to be :debug.

[image] asweet-confluent: I don’t see a good way to structurally prevent this sort of thing from happening again - it seems like it just comes down to “remember to do it right”, which makes me think this is a footgun in Logger rather than something I should be solving. The way to structurally…

I hate logging systems that hide messages by default from me. When initially developing I want to see all the messages without having to mind about configuration.

In Membrane, we have a debug_verbose: boolean flag set via config, defaulting to false, and a corresponding debug_verbose macro. It’s intended for logs that are only useful for debugging the library itself, so we decided to hide them from the user by default. For the regular debugs, I’d prefer if t…

What’s the bar for breaking compatibility? There’s some precedent for doing so when it prevents confusion : feat(logger): return primary level as is, without conversion This is breaking change, but inevitable to not confuse users. Changing the default log level to something safer for production doe…

[image] asweet-confluent: What’s the bar for breaking compatibility? There’s some precedent for doing so when it prevents confusion : Yeah, I know, that is my work. I 100% agree with you that default of :debug is wrong and should be changed, ideally to match Erlang’s :notice, as it would make…

[image] asweet-confluent: What’s the bar for breaking compatibility? For me and my libraries the bar is never. Breaking backward compatibility is a clear sign of code authors don’t give a dime about their users.

[image] hauleth: Unfortunately - no. If that would be possible then I would propose that in the first place, but there is no way to detect that. Couldn’t Logger.App.start/2 detect this by checking both Application.fetch_env(:logger, :level) and the preexisting :logger primary level? If no El…

[image] asweet-confluent: Couldn’t Logger.App.start/2 detect this by checking both Application.fetch_env(:logger, :level) and the preexisting :logger primary level? If no Elixir level is configured and OTP is still at its default :notice, then Logger is about to introduce the implicit :debug. W…

Does that configuration matter here though? Logger.start wipes it out unconditionally . elixir --erl "-kernel logger_level warning" -e ' IO.inspect(Application.get_env(:kernel, :logger_level), label: "kernel.logger_level") IO.inspect(Application.get_env(:logger, :level), label: "Elixir Logger level"…

Why is Logger's default level :debug?

Questions & Help Questions

jhogberg September 12, 2026, 6:49am 3

The way to structurally prevent this from happening is having :debug as a default: you noticed it, didn’t you?