threads_running_logger.rb

EventMachine.run {
  EventMachine::PeriodicTimer.new(60){
    result = ActiveRecord::Base.connection.select_rows("show global status like 'threads_running'") # => [['threads_running', 1]]
    threads_running = result.try(:first).try(:at, 1)

    message = "#{threads_running} threads running at #{Time.now}"
    puts message

    file = File.open("#{Rails.root}/log/mysql_thread_count.log", 'a')
    file.puts message
    file.close
  }
}