Instrumenting ActiveRecord with StatsD

active_record_statsd.rb

ActiveSupport::Notifications.subscribe("sql.active_record") do |name, start, finish, id, payload|
  if payload[:sql] =~ /^\s*(SELECT|DELETE|INSERT|UPDATE) /
    method = $1.downcase
    table  = nil

    # Determine the table name for instrumentation. The below regexes work on
    # mysql but not sqlite. Probably won't work on postgresql either.
    case method
    when "select", "delete"
      table = $1 if payload[:sql] =~ / FROM `(\w+)`/
    when "insert"
      table = $1 if payload[:sql] =~ /^\s*INSERT INTO `(\w+)`/
    when "update"
      table = $1 if payload[:sql] =~ /^\s*UPDATE `(\w+)`/
    end

    # active_record.select
    StatsD.increment("active_record.#{method}")

    if table
      StatsD.increment("active_record.#{table}.#{method}")
      StatsD.timing("active_record.#{table}.#{method}.query_time", (finish - start) * 1000, 1)
    end
  end
end