Ruby benchmarking and benchmarking notes

Profiling.markdown

(because I can't remember anything)

Setup

gem install benchmark-ips
gem install stackprof
gem install allocation_tracer

Stackprof

Will answer questions like "which parts of the code are worth optimizing?"

1. Write something like this

   require "stackprof"
   
   StackProf.run(mode: :cpu, out: "stackprof-cpu-foo.dump") do
     5000.times do
       # code to profile
     end
   end

2. Run the script

3. Run stackprof stackprof-cpu-foo.dump --text

Benchmark/ips

Will answer questions like "which of these two things are the fastest, and by how much?"

1. Write something like this

   require "benchmark/ips"
   
   Benchmark.ips do |x|
     x.report("single") do
       'hi there'
     end
   
     x.report("double") do
       "hi there"
     end
   
     x.compare!
   end

2. Run it

Total object allocations

Will answer questions like "how many total allocations does this code make?"

1. Write something like this

   def objects_allocated_by(iterations: 5000)
     yield
   
     before = GC.stat(:total_allocated_object)
     iterations.times { yield }
     after = GC.stat(:total_allocated_object)
   
     (after - before) / iterations
   end
   
   delta = objects_allocated_by do
     # some code
   end
   
   p delta

2. Run it

Whats types are being allocated

Will answer questions like "how many strings does this code allocate?"

1. Write something like this

   require 'allocation_tracer'
   require 'pp'
   
   ObjectSpace::AllocationTracer.setup(%i{type})
   
   result = ObjectSpace::AllocationTracer.trace do
     5000.times{|i|
       ["a", 1, {}]
     }
   end
   
   pp result

2. Run it