MongoDB Logger Request timing percentile finder

percentile_finder.rb

class PercentileFinder
  attr_accessor :action, :controller, :limit, :calls, :dataset

  def initialize(action, controller, limit = 1000)
    self.action = action
    self.controller = controller
    self.limit = limit
  end

  def find(percentile_looking_for = 0.95)
    populate_dataset unless dataset
    return "No data" if dataset.size == 0
    percentile(dataset, percentile_looking_for)
  end

  def populate_dataset
    db = Rails.logger.mongo_adapter.connection
    collection = Rails.logger.mongo_adapter.collection
    @calls = collection.where({action: action, controller: controller}).sort(request_time: -1).limit(limit)

    self.dataset = []
    @calls.each do |call|
      dataset << call["runtime"]
    end
  end

  def percentile(values, percentile)
    values_sorted = values.sort
    k = (percentile*(values_sorted.length-1)+1).floor - 1
    f = (percentile*(values_sorted.length-1)+1).modulo(1)
    values_sorted[k] + (f * (values_sorted[k+1] - values_sorted[k]))
  end
end

>> require 'percentile_finder'
=> true
>> PercentileFinder.new('index', 'categories', 1000).find(0.95)
=> 1288.2999999999997
>> PercentileFinder.new('index', 'categories', 1000).find(0.5)
=> 352.0