brianhempel · August 28, 2025 07:07 · Feb 19, 2015 · Feb 19, 2015 · Feb 19, 2015
diff --git a/bench_rails_memory_usage.rb b/bench_rails_memory_usage.rb
@@ -0,0 +1,80 @@
+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("[email protected]", "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"