``````require 'benchmark'
``````

## Benchmark

The Benchmark module provides methods to measure and report the time used to execute Ruby code.

• Measure the time to construct the string given by the expression `"a"*1_000_000_000`:

``````require 'benchmark'

puts Benchmark.measure { "a"*1_000_000_000 }
``````

On my machine (OSX 10.8.3 on i5 1.7 GHz) this generates:

``````0.350000   0.400000   0.750000 (  0.835234)
``````

This report shows the user CPU time, system CPU time, the sum of the user and system CPU times, and the elapsed real time. The unit of time is seconds.

• Do some experiments sequentially using the `#bm` method:

``````require 'benchmark'

n = 5000000
Benchmark.bm do |x|
x.report { for i in 1..n; a = "1"; end }
x.report { n.times do   ; a = "1"; end }
x.report { 1.upto(n) do ; a = "1"; end }
end
``````

The result:

``````    user     system      total        real
1.010000   0.000000   1.010000 (  1.014479)
1.000000   0.000000   1.000000 (  0.998261)
0.980000   0.000000   0.980000 (  0.981335)
``````
• Continuing the previous example, put a label in each report:

``````require 'benchmark'

n = 5000000
Benchmark.bm(7) do |x|
x.report("for:")   { for i in 1..n; a = "1"; end }
x.report("times:") { n.times do   ; a = "1"; end }
x.report("upto:")  { 1.upto(n) do ; a = "1"; end }
end
``````

The result:

``````              user     system      total        real
for:      1.010000   0.000000   1.010000 (  1.015688)
times:    1.000000   0.000000   1.000000 (  1.003611)
upto:     1.030000   0.000000   1.030000 (  1.028098)
``````
• The times for some benchmarks depend on the order in which items are run. These differences are due to the cost of memory allocation and garbage collection. To avoid these discrepancies, the #bmbm method is provided. For example, to compare ways to sort an array of floats:

``````require 'benchmark'

array = (1..1000000).map { rand }

Benchmark.bmbm do |x|
x.report("sort!") { array.dup.sort! }
x.report("sort")  { array.dup.sort  }
end
``````

The result:

``````Rehearsal -----------------------------------------
sort!   1.490000   0.010000   1.500000 (  1.490520)
sort    1.460000   0.000000   1.460000 (  1.463025)
-------------------------------- total: 2.960000sec

user     system      total        real
sort!   1.460000   0.000000   1.460000 (  1.460465)
sort    1.450000   0.010000   1.460000 (  1.448327)
``````
• Report statistics of sequential experiments with unique labels, using the #benchmark method:

``````require 'benchmark'
include Benchmark         # we need the CAPTION and FORMAT constants

n = 5000000
Benchmark.benchmark(CAPTION, 7, FORMAT, ">total:", ">avg:") do |x|
tf = x.report("for:")   { for i in 1..n; a = "1"; end }
tt = x.report("times:") { n.times do   ; a = "1"; end }
tu = x.report("upto:")  { 1.upto(n) do ; a = "1"; end }
[tf+tt+tu, (tf+tt+tu)/3]
end
``````

The result:

``````             user     system      total        real
for:      0.950000   0.000000   0.950000 (  0.952039)
times:    0.980000   0.000000   0.980000 (  0.984938)
upto:     0.950000   0.000000   0.950000 (  0.946787)
>total:   2.880000   0.000000   2.880000 (  2.883764)
>avg:     0.960000   0.000000   0.960000 (  0.961255)
``````

Benchmark Reference