See object space used by New Relic (ref: http://stackoverflow.com/questions/3973094/how-to-measure-the-size-of-a-ruby-object http://stackoverflow.com/questions/12397208/memory-grows-indefinitely-in-an-empty-rails-app?rq=1)

memory.rb

#!/bin/env ruby

# lazy hack from Robert Klemme

module Memory
  # sizes are guessed, I was too lazy to look
  # them up and then they are also platform
  # dependent
  REF_SIZE = 4 # ?
  OBJ_OVERHEAD = 4 # ?
  FIXNUM_SIZE = 4 # ?

  # informational output from analysis
  MemoryInfo = Struct.new :roots, :objects, :bytes, :loops

  def self.analyze(*roots)
    an = Analyzer.new
    an.roots = roots
    an.analyze
  end

  class Analyzer
    attr_accessor :roots
    attr_reader   :result

    def analyze
      @result = MemoryInfo.new roots, 0, 0, 0
      @objs = {}

      queue = roots.dup

      until queue.empty?
        obj = queue.shift

        case obj
        # special treatment for some types
        # some are certainly missing from this
        when IO
          visit(obj)
        when String
          visit(obj) { @result.bytes += obj.size }
        when Fixnum
          @result.bytes += FIXNUM_SIZE
        when Array
          visit(obj) do
            @result.bytes += obj.size * REF_SIZE
            queue.concat(obj)
          end
        when Hash
          visit(obj) do
            @result.bytes += obj.size * REF_SIZE * 2
            obj.each {|k,v| queue.push(k).push(v)}
          end
        when Enumerable
          visit(obj) do
            obj.each do |o|
              @result.bytes += REF_SIZE
              queue.push(o)
            end
          end
        else
          visit(obj) do
            obj.instance_variables.each do |var|
              @result.bytes += REF_SIZE
              queue.push(obj.instance_variable_get(var))
            end
          end
        end
      end

      @result
    end

  private
    def visit(obj)
      id = obj.object_id

      if @objs.has_key? id
        @result.loops += 1
        false
      else
        @objs[id] = true
        @result.bytes += OBJ_OVERHEAD
        @result.objects += 1
        yield obj if block_given?
        true
      end
    end
  end
end

profiling_new_relic.rb

ObjectSpace.
  each_object.
  with_object(Hash.new(0)){| obj, h| 
    h[obj.class] = (obj.class.to_s =~ /NewRelic/ ? Memory.analyze(obj).bytes : nil) }.
  select{|k,v| puts "#{k} => #{v}" if k.to_s =~ /NewRelic/}

results.txt

NewRelic::Agent::Configuration::EnvironmentSource => 4
NewRelic::Agent::Configuration::Manager => 423929
NewRelic::Agent::Configuration::DefaultSource => 2588
NewRelic::Agent::TracedMethodStack => 12
NewRelic::Agent::TransactionState => 44
NewRelic::Railtie => 89
NewRelic::LocalEnvironment => 4
NewRelic::Agent::Configuration::ManualSource => 420143
NewRelic::Agent::StartupLogger => 12
NewRelic::Control::Frameworks::Rails3 => 420220
NewRelic::Agent::Configuration::YamlSource => 546
NewRelic::Agent::NullLogger => 4
NewRelic::Agent::AgentLogger => 50
NewRelic::Agent::Commands::XraySessionCollection => 116
NewRelic::Agent::Commands::ThreadProfilerSession => 100
NewRelic::Agent::WorkerLoop => 44
NewRelic::Agent::Threading::BacktraceService => 92
NewRelic::Agent::Commands::AgentCommandRouter => 243
NewRelic::Agent::SqlSampler => 20
NewRelic::Agent::Transaction::ForcePersistSampleBuffer => 12
NewRelic::Agent::Transaction::SlowestSampleBuffer => 12
NewRelic::Agent::Transaction::XraySampleBuffer => 28
NewRelic::Agent::Transaction::DeveloperModeSampleBuffer => 12
NewRelic::Agent::TransactionSampler => 108
NewRelic::Agent::RulesEngine => 4
NewRelic::Agent::StatsHash => 4
NewRelic::Agent::StatsEngine => 28
NewRelic::Agent::EventListener => 164
NewRelic::Agent::NewRelicService::JsonMarshaller => 4
NewRelic::Agent::AuditLogger => 20
NewRelic::Control::Server => 46
NewRelic::Agent::NewRelicService => 150
NewRelic::Agent::Agent => 425851
NewRelic::Agent::SampledBuffer => 44
NewRelic::Agent::RequestSampler => 92
NewRelic::Agent::ErrorCollector => 103
NewRelic::Agent::CrossAppMonitor => 4
NewRelic::Agent::ShimAgent => 424949
NewRelic::Agent::VM::MonotonicGCProfiler => 20
NewRelic::Agent::Harvester => 424949
NewRelic::Agent::JavascriptInstrumentor => 4
NewRelic::Agent::SamplerCollection => 4