A script to test the memory usage of your Rails application over time. It will run 30 requests against the specified action and report the final RSS. Choose the URL to hit on line 45 and then run with `ruby bench_rails_memory_usage.rb`.

bench_rails_memory_usage.rb

require "net/http"

def start_server
  # Remove the X to enable the parameters for tuning.
  # These are the default values as of Ruby 2.2.0.
  @child = spawn(<<-EOC.split.join(" "))
    XRUBY_GC_HEAP_FREE_SLOTS=4096
    XRUBY_GC_HEAP_INIT_SLOTS=10000
    XRUBY_GC_HEAP_GROWTH_FACTOR=1.8
    XRUBY_GC_HEAP_GROWTH_MAX_SLOTS=0
    XRUBY_GC_HEAP_OLDOBJECT_LIMIT_FACTOR=2.0
    XRUBY_GC_MALLOC_LIMIT=16777216
    XRUBY_GC_MALLOC_LIMIT_MAX=33554432
    XRUBY_GC_MALLOC_LIMIT_GROWTH_FACTOR=1.4
    XRUBY_GC_OLDMALLOC_LIMIT=16777216
    XRUBY_GC_OLDMALLOC_LIMIT_MAX=134217728
    XRUBY_GC_OLDMALLOC_LIMIT_GROWTH_FACTOR=1.2
    rails server -p3009 > /dev/null
  EOC
  sleep 0.1 until alive?
end

def alive?
  system("curl http://localhost:3009/ &> /dev/null")
end

def stop_server
  Process.kill "HUP", server_pid
  Process.wait @child
end

def server_pid
  `cat tmp/pids/server.pid`.to_i
end

def memory_size_mb
  (`ps -o rss= -p #{server_pid}`.to_i * 1024).to_f / 2**20
end

# In /etc/hosts I have api.rails.local set to 127.0.0.1 for
# API testing on any app. Curl freaks out and takes extra
# seconds to do the request to these .local things, so we
# will use Net::HTTP for moar speed.
def do_request
  uri = URI("http://api.rails.local:3009/memory_heavy_action")
  req = Net::HTTP::Get.new(uri)
  # Remove the next line if you don't need HTTP basic authentication.
  req.basic_auth("user@example.com", "password")
  req["Content-Type"] = "application/json"

  Net::HTTP.start("localhost", uri.port) do |http|
    http.read_timeout = 60
    http.request(req)
  end
end

results = []

# You can’t just measure once: memory usage has some variance.
# We will take the mean of 7 runs.
7.times do
  start_server

  used_mb = nil
  (1..30).map do |n|
    print "Request #{n}..."
    do_request
    used_mb = memory_size_mb
    puts "#{used_mb} MB"
  end

  final_mb = used_mb
  results << final_mb
  puts "Final Memory: #{final_mb} MB"

  stop_server
end

mean_final_mb = results.reduce(:+) / results.size
puts "Mean Final Memory: #{mean_final_mb} MB"