Ruby Academy · Lesson

Profiling Tools

ruby-prof and stackprof.

Profiling Tools is a free Ruby Academy lesson on CoddyKit — lesson 2 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Ruby Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Benchmark vs Profiler

A benchmark tells you how long something takes. A profiler tells you where the time goes inside it.

Profilers break time down per method or line
They reveal hotspots you would never guess
Popular Ruby profilers: ruby-prof and stackprof

# Profilers answer: which method consumed the most time?
puts 'Benchmark = how long, Profiler = where'

ruby-prof Overview

ruby-prof is a detailed instrumenting profiler. It hooks into every method call.

Very precise call counts and timings
Higher overhead, so use on representative samples
Installed with gem install ruby-prof

# Gemfile
gem 'ruby-prof'

Profiling a Block with ruby-prof

Wrap code in RubyProf.profile to capture a result you can print.

Returns a profile result object
Feed it to a printer for output

require 'ruby-prof'

result = RubyProf.profile do
  1000.times { |i| (1..i).reduce(:+) }
end

RubyProf::FlatPrinter.new(result).print(STDOUT)

ruby-prof Printers

ruby-prof offers several printers for different views.

FlatPrinter a sorted list of methods
GraphPrinter caller/callee relationships
CallTreePrinter output for KCachegrind

require 'ruby-prof'

result = RubyProf.profile { 100.times { 'x' * 1000 } }
RubyProf::GraphPrinter.new(result).print(STDOUT, min_percent: 1)

Reading a Flat Profile

A flat profile lists methods by time consumed.

%self time spent in the method itself
total time including callees
calls how many times invoked

Focus on the highest %self entries first.

# Example flat output columns:
# %self  total  self  wait  child  calls  name
puts 'Optimize the top %self method first'

stackprof Overview

stackprof is a sampling profiler. It periodically records the call stack.

Very low overhead, safe for production
Samples by CPU, wall, or object allocation
Installed with gem install stackprof

# Gemfile
gem 'stackprof'

Running stackprof

StackProf.run profiles a block and writes results to a file.

mode: can be :cpu, :wall, or :object
out: sets the dump file path

require 'stackprof'

StackProf.run(mode: :cpu, out: 'profile.dump') do
  1_000_000.times { |i| Math.sqrt(i) }
end

Inspecting stackprof Results

Use the stackprof command line tool to read the dump.

stackprof profile.dump --text for a summary
--method Name#meth drills into one method
--flamegraph produces flamegraph data

# Shell
# stackprof profile.dump --text
# stackprof profile.dump --method 'Array#sort'
puts 'Analyze the dump with the stackprof CLI'

Sampling vs Instrumenting

The two profilers trade accuracy for overhead.

ruby-prof instruments every call: exact but slower
stackprof samples: approximate but cheap
Use stackprof in production, ruby-prof for deep dives

modes = { 'ruby-prof' => 'instrumenting', 'stackprof' => 'sampling' }
modes.each { |tool, kind| puts "#{tool}: #{kind}" }

Wall vs CPU Time

Choose the profiling mode based on the bottleneck.

CPU mode shows compute heavy code
Wall mode also captures I/O waits like network or disk
Slow endpoints with DB calls need wall mode

# I/O bound? use wall. CPU bound? use cpu.
bottleneck = 'database query'
mode = bottleneck.include?('query') ? :wall : :cpu
puts "Use mode: #{mode}"

A Profiling Workflow

Effective profiling follows a loop.

Reproduce the slow scenario
Profile to find the hotspot
Optimize only that hotspot
Re-profile to confirm improvement

steps = ['reproduce', 'profile', 'optimize hotspot', 're-profile']
steps.each_with_index { |s, i| puts "#{i + 1}. #{s}" }

Quick Check

Test your profiling knowledge.

Recap

You learned about profiling tools:

Profilers show where time is spent, not just how long
ruby-prof instruments every call for precise detail
stackprof samples cheaply, safe for production
Choose CPU vs wall mode based on the bottleneck
Follow the reproduce, profile, optimize, re-profile loop

Next you will reduce memory allocations.

Frequently asked questions

Is the “Profiling Tools” lesson free?

Yes — the full text of “Profiling Tools” is free to read here on the web, and the Ruby Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Ruby Academy course, upgrade to CoddyKit PRO.

What will I learn in “Profiling Tools”?

ruby-prof and stackprof. You practise Ruby Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Ruby Academy?

No prior experience is required. Ruby Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Profiling Tools” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Ruby Academy lesson?

Yes. Every Ruby Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

← Back to Ruby Academy