Benchmarking conditionals vs exceptions

benchmark_if_vs_exception.rb

require 'benchmark/ips'

def expensive_operation duration=0.001
  sleep duration
  false
end

Benchmark.ips do |x|
  x.report 'simple if' do
    if false
      whatever
    else
      false
    end
  end

  x.report 'simple exception' do
    begin
      if false
        whatever
      else
        raise ArgumentError, "omg"
      end
    rescue ArgumentError => e
    end
  end

  x.compare!
end

Benchmark.ips do |x|
  x.report 'expensive if' do
    if expensive_operation
      whatever
    else
      false
    end
  end

  x.report 'expensive exception' do
    begin
      if expensive_operation
        whatever
      else
        raise ArgumentError, "omg"
      end
    rescue ArgumentError => e
    end
  end

  x.compare!
end

results.md

Microbenchmark shows conditionals are wildly faster:

Warming up --------------------------------------
           simple if   416.263k i/100ms
    simple exception   105.397k i/100ms
Calculating -------------------------------------
           simple if     16.148M (± 1.5%) i/s -     80.755M in   5.002331s
    simple exception      1.298M (± 1.8%) i/s -      6.535M in   5.034078s

Comparison:
           simple if: 16147688.0 i/s
    simple exception:  1298493.6 i/s - 12.44x  slower

This looks terrible. The example without the exception is over 12x as fast. We could do 15 MILLION more iterations per second if not for the exception handling!

In the "expensive" example, we add 1 millisecond of sleep to simulate a small level of work. In a request to a Rails app, you're almost guaranteed to be spending more than 1ms (one DB query alone is likely to blow past that), but this is just to illustrate the effect that even a tiny amount of work has on that 12x factor we saw above. Have a gander at the result:

Warming up --------------------------------------
        expensive if    76.000  i/100ms
 expensive exception    74.000  i/100ms
Calculating -------------------------------------
        expensive if    741.318  (± 1.6%) i/s -      3.724k in   5.024683s
 expensive exception    744.120  (± 3.2%) i/s -      3.774k in   5.076659s

Comparison:
 expensive exception:      744.1 i/s
        expensive if:      741.3 i/s - same-ish: difference falls within error

The difference disappears completely. The exception resulted in virtually no performance penalty.