PidController

This is a Ruby implementation of a PID Controller. A PID controller is a feedback system that is configured with a target setpoint, can read measurements of the system to see how close we are to the setpoint, and will omit an output. Every day examples include:

• Cruise control
• Thermostats
• Quadcopters (appearently, because they predominate search results)
• Database load (yay! This is why the purpose I'm actually writing this for).

Recommended reading

• PID without a PhD
• Throttling Utilities in the IBM DB2 Universal Database Server

Usage

I mentioned databases, so here's an example of how we can prevent a low priority task (e.g. bulk deletion) from contending with customer traffic:

sensor = MySQLSensor.new # Use your imagination
controller = PIDController.new(
  setpoint: 60.0,
  kp: 5.0,
  ki: 1.0,
  kd: 0.1,
  output_max: 0.0,
  integral_max: 0.0
  )

Event.where(account_id: account_id).in_batches do |relation|
  relation.delete_all
  backoff = -1 * controller << sensor.cpu_utilization
  sleep backoff if backoff > 0
end

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/gabetax/pid_controller.