discourse/config/initializers/100-silence_logger.rb

class SilenceLogger < Rails::Rack::Logger
  PATH_INFO = 'PATH_INFO'.freeze
  HTTP_X_SILENCE_LOGGER = 'HTTP_X_SILENCE_LOGGER'.freeze

  def initialize(app, opts = {})
    @app = app
    @opts = opts
    @opts[:silenced] ||= []

    # Rails introduces something called taggers in the Logger, needs to be initialized
    super(app)
  end

  def call(env)
    prev_level = Rails.logger.level
    path_info = env[PATH_INFO]

    if    env[HTTP_X_SILENCE_LOGGER] ||
          @opts[:silenced].include?(path_info) ||
          path_info.start_with?('/logs') ||
          path_info.start_with?('/user_avatar') ||
          path_info.start_with?('/letter_avatar')
      Rails.logger.level = Logger::WARN
      @app.call(env)
    else
      super(env)
    end
  ensure
    Rails.logger.level = prev_level
  end
end

silenced = [
  "/mini-profiler-resources/results".freeze,
  "/mini-profiler-resources/includes.js".freeze,
  "/mini-profiler-resources/includes.css".freeze,
  "/mini-profiler-resources/jquery.tmpl.js".freeze
]
Rails.configuration.middleware.swap Rails::Rack::Logger, SilenceLogger, silenced: silenced