[Proposal] Logger.put_process_level/2

[Stefan Chrobot]

Hi, I'd like to propose an addition of put_process_level(pid, level) into the Logger module to allow controlling the runtime logging level on a per-process basis.

Our app runs multiple background processing jobs that are performing data sync. This means that the jobs run "forever". We're running a job (OTP process) for each user. While we have metrics and alerts to understand when a new user is hitting some bumps, we'd like to have detailed logs to help debug any potential issues. The issues are mostly data-dependent and are happening in the initial phase of the sync. After that, the issues rarely ever happen and so the detailed logs are pretty useless, but they still consume resources.

We could address our use case with something like the following:

new? = DateTime.diff(DateTime.utc_now(), sync_start) > @threshold

Logger.put_process_level(self(), if new?, do: :debug, else: :warn)

The implementation should be pretty straightforward and resemble the implementation of Logger.enable/1.

Looking forward to your thoughts.

Best,

Stefan

[José Valim]

Sounds good to me, a PR is welcome! We should actually change Logger.enable to use the new Logger.put_process_level, especially because we have two meta-levels called :none and :all.

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[Stefan Chrobot]

On it's way!

Thanks,

Stefan

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[luk...@niemier.pl]

There was discussion about that in OTP repository. Unfortunately it is not possible with current implementation of logger, as you cannot lower the requirement below default level per process, it is simply not supported by the OTP logger.

https://github.com/erlang/otp/pull/2384

[José Valim]

Hi Łukasz,

Can you please expand what you mean? We already added Logger.put_process_level/2, which applies only to the current process at the moment. So it seems there is a pitfall we may need to document? I believe a process cannot override the general log level, is that correct? In other words, it can only be used to have a more restricted one.

Thanks!

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