# Benchee [](https://hex.pm/packages/benchee) [](https://hexdocs.pm/benchee/) [](https://travis-ci.org/bencheeorg/benchee) [](https://ci.appveyor.com/project/PragTob/benchee-8e4gw) [](https://coveralls.io/github/bencheeorg/benchee?branch=master)
Library for easy and nice (micro) benchmarking in Elixir. Benchee allows you to compare the performance of different pieces of code at a glance. It is also versatile and extensible, relying only on functions. There are also a bunch of [plugins](#plugins) to draw pretty graphs and more!
benchee runs each of your functions for a given amount of time after an initial warmup, it then measures their run time and optionally memory consumption. It then shows different statistical values like average, standard deviation etc. See [features](#features)
benchee has a nice and concise main interface, its behavior can be altered through lots of [configuration options](#configuration):
```elixir
list = Enum.to_list(1..10_000)
map_fun = fn i -> [i, i * i] end
Benchee.run(
%{
"flat_map" => fn -> Enum.flat_map(list, map_fun) end,
"map.flatten" => fn -> list |> Enum.map(map_fun) |> List.flatten() end
},
time: 10,
memory_time: 2
)
```
Produces the following output on the console:
```
tobi@speedy:$ mix run samples/run.exs
Operating System: Linux
CPU Information: Intel(R) Core(TM) i7-4790 CPU @ 3.60GHz
Number of Available Cores: 8
Available memory: 15.61 GB
Elixir 1.8.1
Erlang 21.2.7
Benchmark suite executing with the following configuration:
warmup: 2 s
time: 10 s
memory time: 2 s
parallel: 1
inputs: none specified
Estimated total run time: 28 s
Benchmarking flat_map...
Benchmarking map.flatten...
Name ips average deviation median 99th %
flat_map 2.34 K 426.84 μs ±9.88% 418.72 μs 720.20 μs
map.flatten 1.18 K 844.08 μs ±19.73% 778.10 μs 1314.87 μs
Comparison:
flat_map 2.34 K
map.flatten 1.18 K - 1.98x slower +417.24 μs
Memory usage statistics:
Name Memory usage
flat_map 624.97 KB
map.flatten 781.25 KB - 1.25x memory usage +156.28 KB
**All measurements for memory usage were the same**
```
The aforementioned [plugins](#plugins) like [benchee_html](https://github.com/bencheeorg/benchee_html) make it possible to generate nice looking [html reports](https://www.pragtob.info/benchee/flat_map.html), where individual graphs can also be exported as PNG images:
## Features
* first runs the functions for a given warmup time without recording the results, to simulate a _"warm"/running_ system
* [measures memory usage](#measuring-memory-consumption)
* provides you with lots of statistics - check the next list
* plugin/extensible friendly architecture so you can use different formatters to display benchmarking results as [HTML, markdown, JSON and more](#plugins)
* nicely formatted console output with units scaled to appropriately (nanoseconds to minutes)
* measures the overhead of function calls so that the measured/reported times really are the execution time of _your_code_ without that overhead.
* [hooks](#hooks-setup-teardown-etc) to execute something before/after a benchmarking invocation
* execute benchmark jobs in parallel to gather more results in the same time, or simulate a system under load
* well documented & well tested
Provides you with the following **statistical data**:
* **average** - average execution time/memory usage (the lower the better)
* **ips** - iterations per second, aka how often can the given function be executed within one second (the higher the better - good for graphing), only for run times
* **deviation** - standard deviation (how much do the results vary), given as a percentage of the average (raw absolute values also available)
* **median** - when all measured values are sorted, this is the middle value. More stable than the average and somewhat more likely to be a typical value you see, for the msot typical value see mode. (the lower the better)
* **99th %** - 99th percentile, 99% of all measured values are less than this - worst case performance-ish
In addition, you can optionally output an extended set of statistics:
* **minimum** - the smallest value measured for the job (fastest/least consumption)
* **maximum** - the biggest run time measured for the job (slowest/most consumption)
* **sample size** - the number of measurements taken
* **mode** - the measured values that occur the most. Often one value, but can be multiple values if they occur the same amount of times. If no value occurs at least twice, this value will be nil.
## Installation
Add benchee to your list of dependencies in `mix.exs`:
```elixir
defp deps do
[{:benchee, "~> 1.0", only: :dev}]
end
```
Install via `mix deps.get` and then happy benchmarking as described in [Usage](#usage) :)
Elixir versions supported/tested against are 1.6+. It _should_ theoretically still work with 1.4 & 1.5 but we don't actively test/support it.
## Usage
After installing just write a little Elixir benchmarking script:
```elixir
list = Enum.to_list(1..10_000)
map_fun = fn i -> [i, i * i] end
Benchee.run(
%{
"flat_map" => fn -> Enum.flat_map(list, map_fun) end,
"map.flatten" => fn -> list |> Enum.map(map_fun) |> List.flatten() end
}
)
```
(names can also be specified as `:atoms` if you want to)
This produces the following output:
```
tobi@speedy:$ mix run samples/run_defaults.exs
Operating System: Linux
CPU Information: Intel(R) Core(TM) i7-4790 CPU @ 3.60GHz
Number of Available Cores: 8
Available memory: 15.61 GB
Elixir 1.8.1
Erlang 21.2.7
Benchmark suite executing with the following configuration:
warmup: 2 s
time: 5 s
memory time: 0 ns
parallel: 1
inputs: none specified
Estimated total run time: 14 s
Benchmarking flat_map...
Benchmarking map.flatten...
Name ips average deviation median 99th %
flat_map 2.34 K 427.78 μs ±16.02% 406.29 μs 743.01 μs
map.flatten 1.22 K 820.87 μs ±19.29% 772.61 μs 1286.35 μs
Comparison:
flat_map 2.34 K
map.flatten 1.22 K - 1.92x slower +393.09 μs
```
See [Features](#features) for a description of the different statistical values and what they mean.
If you're looking to see how to make something specific work, please refer to the [samples](https://github.com/PragTob/benchee/tree/master/samples) directory. Also, especially when wanting to extend benchee, check out the [hexdocs](https://hexdocs.pm/benchee/api-reference.html).
### Configuration
Benchee takes a wealth of configuration options, however those are entirely optional. Benchee ships with sensible defaults for all of these.
In the most common `Benchee.run/2` interface configuration options are passed as the second argument in the form of an keyword list:
```elixir
Benchee.run(%{"some function" => fn -> magic end}, print: [benchmarking: false])
```
The available options are the following (also documented in [hexdocs](https://hexdocs.pm/benchee/Benchee.Configuration.html#init/1)).
* `warmup` - the time in seconds for which a benchmarking job should be run without measuring anything before "real" measurements start. This simulates a _"warm"/running_ system. Defaults to 2.
* `time` - the time in seconds for how long each individual scenario (benchmarking job x input) should be run for measuring the execution times (run time performance). Defaults to 5.
* `memory_time` - the time in seconds for how long [memory measurements](measuring-memory-consumption) should be conducted. Defaults to 0 (turned off).
* `inputs` - a map or list of two element tuples. If a map, they keys are descriptive input names and values are the actual input values. If a list of tuples, the first element in each tuple is the input name, and the second element in each tuple is the actual input value. Your benchmarking jobs will then be run with each of these inputs. For this to work your benchmarking function gets the current input passed in as an argument into the function. Defaults to `nil`, aka no input specified and functions are called without an argument. See [Inputs](#inputs).
* `formatters` - list of formatters either as a module implementing the formatter behaviour, a tuple of said module and options it should take or formatter functions. They are run when using `Benchee.run/2` or you can invoke them through `Benchee.Formatter.output/1`. Functions need to accept one argument (which is the benchmarking suite with all data) and then use that to produce output. Used for plugins & configuration. Also allows the configuration of the console formatter to print extended statistics. Defaults to the builtin console formatter `Benchee.Formatters.Console`. See [Formatters](#formatters).
* `:measure_function_call_overhead` - Measure how long an empty function call takes and deduct this from each measured run time. Defaults to true.
* `pre_check` - whether or not to run each job with each input - including all given before or after scenario or each hooks - before the benchmarks are measured to ensure that your code executes without error. This can save time while developing your suites. Defaults to `false`.
* `parallel` - the function of each benchmarking job will be executed in `parallel` number processes. If `parallel: 4` then 4 processes will be spawned that all execute the _same_ function for the given time. When these finish/the time is up 4 new processes will be spawned for the next scenario. This gives you more data in the same time, but also puts a load on the system interfering with benchmark results. For more on the pros and cons of parallel benchmarking [check the wiki](https://github.com/bencheeorg/benchee/wiki/Parallel-Benchmarking). Defaults to 1 (no parallel execution).
* `save` - specify a `path` where to store the results of the current benchmarking suite, tagged with the specified `tag`. See [Saving & Loading](#saving-loading-and-comparing-previous-runs).
* `load` - load saved suit or suits to compare your current benchmarks against. Can be a string or a list of strings or patterns. See [Saving & Loading](#saving-loading-and-comparing-previous-runs).
* `print` - a map or keyword list from atoms to `true` or `false` to configure if the output identified by the atom will be printed during the standard benchee benchmarking process. All options are enabled by default (true). Options are:
* `:benchmarking` - print when Benchee starts benchmarking a new job (`Benchmarking name ...`)
* `:configuration` - a summary of configured benchmarking options including estimated total run time is printed before benchmarking starts
* `:fast_warning` - warnings are displayed if functions are executed too fast leading to inaccurate measures
* `:unit_scaling` - the strategy for choosing a unit for durations,
counts & memory measurements. May or may not be implemented by a given formatter (The console formatter implements it).
When scaling a value, benchee finds the "best fit"
unit (the largest unit for which the result is at least 1). For example,
1_200_000 scales to `1.2 M`, while `800_000` scales to `800 K`. The
`unit_scaling` strategy determines how benchee chooses the best fit unit for
an entire list of values, when the individual values in the list may have
different best fit units. There are four strategies, defaulting to `:best`:
* `:best` - the most frequent best fit unit will be used, a tie
will result in the larger unit being selected.
* `:largest` - the largest best fit unit will be used
* `:smallest` - the smallest best fit unit will be used
* `:none` - no unit scaling will occur.
* `:before_scenario`/`after_scenario`/`before_each`/`after_each` - read up on them in the [hooks section](#hooks-setup-teardown-etc)
### Measuring memory consumption
Starting with version 0.13, users can now get measurements of how much memory their benchmarked scenarios use. The measurement is **limited to the process that benche executes your provided code in** - i.e. other processes (like worker pools)/the whole BEAM isn't taken into account.
This measurement is **not** the actual effect on the size of the BEAM VM size, but the total amount of memory that was allocated during the execution of a given scenario. This includes all memory that was garbage collected during the execution of that scenario.
This measurement of memory does not affect the measurement of run times.
In cases where all measurements of memory consumption are identical, which happens very frequently, the full statistics will be omitted from the standard console formatter. If your function is deterministic, this should always be the case. Only in functions with some amount of randomness will there be variation in memory usage.
Memory measurement is disabled by default, and you can choose to enable it by passing `memory_time: your_seconds` option to `Benchee.run/2`:
```elixir
Benchee.run(
%{
"something_great" => fn -> cool_stuff end
},
memory_time: 2
)
```
Memory time can be specified separately as it will often be constant - so it might not need as much measuring time.
A full example, including an example of the console output, can be found
[here](samples/measure_memory.exs).
### Inputs
`:inputs` is a very useful configuration that allows you to run the same benchmarking jobs with different inputs. We call this combination a _"scenario"_. You specify the inputs as either a map from name (String or atom) to the actual input value or a list of tuples where the first element in each tuple is the name and the second element in the tuple is the value.
Why do this? Functions can have different performance characteristics on differently shaped inputs - be that structure or input size. One of such cases is comparing tail-recursive and body-recursive implementations of `map`. More information in the [repository with the benchmark](https://github.com/PragTob/elixir_playground/blob/master/bench/tco_blog_post_focussed_inputs.exs) and the [blog post](https://pragtob.wordpress.com/2016/06/16/tail-call-optimization-in-elixir-erlang-not-as-efficient-and-important-as-you-probably-think/).
As a little sample:
```elixir
map_fun = fn i -> [i, i * i] end
Benchee.run(
%{
"flat_map" => fn input -> Enum.flat_map(input, map_fun) end,
"map.flatten" => fn input -> input |> Enum.map(map_fun) |> List.flatten() end
},
inputs: %{
"Small" => Enum.to_list(1..1_000),
"Medium" => Enum.to_list(1..10_000),
"Bigger" => Enum.to_list(1..100_000)
}
)
```
This means each function will be benchmarked with each input that is specified in the inputs. Then you'll get the output divided by input so you can see which function is fastest for which input, like so:
```
tobi@speedy:~/github/benchee(readme-overhaul)$ mix run samples/multiple_inputs.exs
(... general information ...)
##### With input Bigger #####
Name ips average deviation median 99th %
flat_map 150.81 6.63 ms ±12.65% 6.57 ms 8.74 ms
map.flatten 114.05 8.77 ms ±16.22% 8.42 ms 12.76 ms
Comparison:
flat_map 150.81
map.flatten 114.05 - 1.32x slower +2.14 ms
##### With input Medium #####
Name ips average deviation median 99th %
flat_map 2.28 K 437.80 μs ±10.72% 425.63 μs 725.09 μs
map.flatten 1.78 K 561.18 μs ±5.55% 553.98 μs 675.98 μs
Comparison:
flat_map 2.28 K
map.flatten 1.78 K - 1.28x slower +123.37 μs
##### With input Small #####
Name ips average deviation median 99th %
flat_map 26.31 K 38.01 μs ±15.47% 36.69 μs 67.08 μs
map.flatten 18.65 K 53.61 μs ±11.32% 52.79 μs 70.17 μs
Comparison:
flat_map 26.31 K
map.flatten 18.65 K - 1.41x slower +15.61 μs
```
Therefore, we **highly recommend** using this feature and checking different realistically structured and sized inputs for the functions you benchmark!
### Formatters
Among all the configuration options, one that you probably want to use are the formatters. They format and print out the results of the benchmarking suite.
The `:formatters` option is specified a list of:
* modules implementing the `Benchee.Formatter` behaviour
* a tuple of a module specified above and options for it `{module, options}`
* functions that take one argument (the benchmarking suite with all its results) and then do whatever you want them to
So if you are using the [HTML plugin](https://github.com/bencheeorg/benchee_html) and you want to run both the console formatter and the HTML formatter this looks like this (after you installed it of course):
```elixir
list = Enum.to_list(1..10_000)
map_fun = fn i -> [i, i * i] end
Benchee.run(
%{
"flat_map" => fn -> Enum.flat_map(list, map_fun) end,
"map.flatten" => fn -> list |> Enum.map(map_fun) |> List.flatten end
},
formatters: [
{Benchee.Formatters.HTML, file: "samples_output/my.html"},
Benchee.Formatters.Console
]
)
```
#### Console Formatter options
The console formatter supports 2 configuration options:
* `:comparison` - if the comparison of the different benchmarking jobs (x times slower than) is shown. Enabled by default.
* `extended_statistics` - display more statistics, aka `minimum`, `maximum`, `sample_size` and `mode`. Disabled by default.
So if you want to see more statistics you simple pass `extended_statistics: true` to the console formatter:
```elixir
list = Enum.to_list(1..10_000)
map_fun = fn i -> [i, i * i] end
Benchee.run(
%{
"flat_map" => fn -> Enum.flat_map(list, map_fun) end,
"map.flatten" => fn -> list |> Enum.map(map_fun) |> List.flatten() end
},
time: 10,
formatters: [{Benchee.Formatters.Console, extended_statistics: true}]
)
```
Which produces:
```
(... normal output ...)
Extended statistics:
Name minimum maximum sample size mode
flat_map 345.43 μs 1195.89 μs 23.73 K 405.64 μs
map.flatten 522.99 μs 2105.56 μs 12.03 K 767.83 μs, 768.44 μs
```
(Btw. notice how the modes of both are much closer and for `map.flatten` much less than the average of `766.99`, see `samples/run_extended_statistics`)
### Saving, loading and comparing previous runs
Benchee can store the results of previous runs in a file and then load them again to compare them. For example this is useful to compare what was recorded on the master branch against a branch with performance improvements.
**Saving** is done through the `save` configuration option. You can specify a `path` where results are saved, or you can use the default option of`"benchmark.benchee"` if you don't pass a `path`. You can also pass a `tag` option which annotates these results (for instance with a branch name). The default option for the `tag` is a timestamp of when the benchmark was run.
**Loading** is done through the `load` option specifying a path to the file to
load (for instance `"benchmark.benchee"`). You can also specify multiple files to load through a list of paths (`["my.benchee", "master_save.benchee"]`) - each one of those can also be a glob expression to match even more files glob (`"save_number*.benchee"`).
```elixir
Benchee.run(
%{
"something_great" => fn -> cool_stuff end
},
save: [path: "save.benchee", tag: "first-try"]
)
Benchee.run(%{}, load: "save.benchee")
```
In the more verbose API this is triggered via `Benchee.load/1`.
### Hooks (Setup, Teardown etc.)
Most of the time, it's best to keep your benchmarks as simple as possible: plain old immutable functions work best. But sometimes you need other things to happen. When you want to add before or after hooks to your benchmarks, we've got you covered! Before you dig into this section though remember one thing: **you usually don't need hooks!**
Benchee has three types of hooks:
* [Suite hooks](#suite-hooks)
* [Scenario hooks](#scenario-hooks)
* [Benchmarking function hooks](#benchmarking-function-hooks)
Of course, **hooks are not included in the measurements**. So they are there especially if you want to do something and want it to **not be included in the measurements**. Sadly there is the notable exception of _too_fast_functions_ (the ones that execute faster than we can measure in _native_ resolution). As we need to measure their repeated invocations to get halfway good measurements `before_each` and `after_each` hooks are included there. However, to the best of our knowledge this should only ever happen on Windows (because of the bad run time measurement accuracy).
#### Suite hooks
It is very easy in benchee to do setup and teardown for the whole benchmarking suite (think: "before all" and "after all"). As benchee is just plain old functions, just do your setup and teardown before/after you call benchee:
```elixir
your_setup()
Benchee.run(%{"Awesome stuff" => fn -> magic end})
your_teardown()
```
_When might this be useful?_
* Seeding the database with data to be used by all benchmarking functions
* Starting/shutting down a server, process, other dependencies
#### Scenario hooks
For the following discussions, it's important to know what benchee considers a "benchmarking scenario".
##### What is a scenario?
A scenario is the combination of one benchmarking function and one input. So, given this benchmark:
```elixir
Benchee.run(
%{
"foo" => fn input -> ... end,
"bar" => fn input -> ... end
},
inputs: %{
"input 1" => 1,
"input 2" => 2
}
)
```
there are 4 scenarios:
1. foo with input 1
2. foo with input 2
3. bar with input 1
4. bar with input 2
A scenario includes warmup and actual run time (+ other measurements like memory).
##### before_scenario
Is executed before every [scenario](#what-is-a-scenario) that it applies to (see [hook configuration](#hook-configuration-global-versus-local)). `before_scenario` hooks take the input of the scenario as an argument.
Since the return value of a `before_scenario` becomes the input for next steps (see [hook arguments and return values](#hook-arguments-and-return-values)), there usually are 3 kinds of before scenarios:
* you just want to invoke a side effect: in that case return the given input unchanged
* you want to alter the given input: in that case alter the given input
* you want to keep the given input but add some other data: in that case return a tuple like `{original_input, new_fancy_data}`
For before scenario hooks, the _global_ hook is invoked first, then the _local_ (see [when does a hook happen?](#when-does-a-hook-happen-complete-example)).
Usage:
```elixir
Benchee.run(
%{
"foo" =>
{
fn {input, resource} -> foo(input, resource) end,
before_scenario: fn {input, resource} ->
resource = alter_resource(resource)
{input, resource}
end
},
"bar" =>
fn {input, resource} -> bar(input, resource) end
},
inputs: %{"input 1" => 1},
before_scenario: fn input ->
resource = start_expensive_resource()
{input, resource}
end
)
```
_When might this be useful?_
* Starting a process to be used in your scenario
* Recording the PID of `self()` for use in your benchmark (each scenario is executed in its own process, so scenario PIDs aren't available in functions running before the suite)
* Clearing the cache before a scenario
##### after_scenario
Is executed after a scenario has completed. After scenario hooks receive the return value of the last `before_scenario` that ran as an argument. The return value is discarded (see [hook arguments and return values](#hook-arguments-and-return-values)).
For after scenario hooks, the _local_ hook is invoked first, then the _global_ (see [when does a hook happen?](#when-does-a-hook-happen-complete-example)).
Usage:
```elixir
Benchee.run(
%{
"bar" => fn -> bar() end
},
after_scenario: fn _input -> bust_my_cache() end
)
```
_When might this be useful?_
* Busting caches after a scenario completed
* Deleting all the records in the database that the scenario just created
* Terminating whatever was setup by `before_scenario`
#### Benchmarking function hooks
You can also schedule hooks to run before and after each invocation of a benchmarking function.
##### before_each
Is executed before each invocation of the benchmarking function (before every measurement). Before each hooks receive the return value of their `before_scenario` hook as their argument. The return value of a before each hook becomes the input to the benchmarking function (see [hook arguments and return values](#hook-arguments-and-return-values)).
For before each hooks, the _global_ hook is invoked first, then the _local_ (see [when does a hook happen?](#when-does-a-hook-happen-complete-example)).
Usage:
```elixir
Benchee.run(
%{
"bar" => fn record -> bar(record) end
},
inputs: %{ "record id" => 1},
before_each: fn input -> get_from_db(input) end
)
```
_When might this be useful?_
* Retrieving a record from the database and passing it on to the benchmarking function to do _something(tm)_ without the retrieval from the database adding to the benchmark measurement
* Busting caches so that all measurements are taken in an uncached state
* Picking a random value from a collection and passing it to the benchmarking function for measuring performance with a wider spread of values
* you could also use this to benchmark with random data like `StreamData`, [devon shows how it's done here](https://devonestes.herokuapp.com/benchmarking-with-stream-data)
##### after_each
Is executed directly after the invocation of the benchmarking function. After each hooks receive the return value of the benchmarking function as their argument. The return value is discarded (see [hook arguments and return values](#hook-arguments-and-return-values)).
For after each hooks, the _local_ hook is invoked first, then the _global_ (see [when does a hook happen?](#when-does-a-hook-happen-complete-example)).
Usage:
```elixir
Benchee.run(
%{
"bar" => fn input -> bar(input) end
},
inputs: %{ "input 1" => 1},
after_each: fn result -> assert result == 42 end
)
```
_When might this be useful?_
* Running assertions that whatever your benchmarking function returns is truly what it should be (i.e. all "contestants" work as expected)
* Busting caches/terminating processes setup in `before_each` or elsewhere
* Deleting files created by the benchmarking function
#### Hook arguments and return values
Before hooks form a chain, where the return value of the previous hook becomes the argument for the next one. The first defined `before` hook receives the scenario input as an argument, and returns a value that becomes the argument of the next in the chain. The benchmarking function receives the value of the last `before` hook as its argument (or the scenario input if there are no `before` hooks).
After hooks do not form a chain, and their return values are discarded. An `after_each` hook receives the return value of the benchmarking function as its argument. An `after_scenario` function receives the return value of the last `before_scenario` that ran (or the scenario's input if there is no `before_scenario` hook).
If you haven't defined any inputs, the hook chain is started with the special input argument returned by `Benchee.Benchmark.no_input()`.
#### Hook configuration: global versus local
Hooks can be defined either _globally_ as part of the configuration or _locally_ for a specific benchmarking function. Global hooks will be executed for every scenario in the suite. Local hooks will only be executed for scenarios involving that benchmarking function.
**Global hooks**
Global hooks are specified as part of the general benchee configuration:
```elixir
Benchee.run(
%{
"foo" => fn input -> ... end,
"bar" => fn input -> ... end
},
inputs: %{
"input 1" => 1,
"input 2" => 2,
},
before_scenario: fn input -> ... end
)
```
Here the `before_scenario` function will be executed for all 4 scenarios present in this benchmarking suite.
**Local hooks**
Local hooks are defined alongside the benchmarking function. To define a local hook, pass a tuple in the initial map, instead of just a single function. The benchmarking function comes first, followed by a keyword list specifying the hooks to run:
```elixir
Benchee.run(
%{
"foo" => {fn input -> ... end, before_scenario: fn input -> ... end},
"bar" => fn input -> ... end
},
inputs: %{
"input 1" => 1,
"input 2" => 2
}
)
```
Here `before_scenario` is only run for the 2 scenarios associated with `"foo"`, i.e. foo with input 1 and foo with input 2. It is _not_ run for any `"bar"` benchmarks.
#### When does a hook happen? (Complete Example)
Yes the whole hooks system is quite a lot to take in. Here is an overview showing the order of hook execution, along with the argument each hook receives (see [hook arguments and return values](#hook-arguments-and-return-values)). The guiding principle whether _local_ or _global_ is run first is that _local_ always executes closer to the benchmarking function.
Given the following code:
```elixir
suite_set_up()
Benchee.run(
%{
"foo" =>
{
fn input -> foo(input) end,
before_scenario: fn input ->
local_before_scenario(input)
input + 1
end,
before_each: fn input ->
local_before_each(input)
input + 1
end,
after_each: fn value ->
local_after_each(value)
end,
after_scenario: fn input ->
local_after_scenario(input)
end
},
"bar" =>
fn input -> bar(input) end
},
inputs: %{"input 1" => 1},
before_scenario: fn input ->
global_before_scenario(input)
input + 1
end,
before_each: fn input ->
global_before_each(input)
input + 1
end,
after_each: fn value ->
global_after_each(value)
end,
after_scenario: fn input ->
global_after_scenario(input)
end
)
suite_tear_down()
```
Keeping in mind that the order of foo and bar could be different, here is how the hooks are called:
```
suite_set_up
# starting with the foo scenario
global_before_scenario(1)
local_before_scenario(2) # as before_scenario incremented it
global_before_each(3)
local_before_each(4)
foo(5) # let's say foo(5) returns 6
local_after_each(6)
global_after_each(6)
global_before_each(3)
local_before_each(4)
foo(5) # let's say foo(5) returns 6
local_after_each(6)
global_after_each(6)
# ... this block is repeated as many times as benchee has time
local_after_scenario(3)
global_after_scenario(3)
# now it's time for the bar scenario, it has no hooks specified for itself
# so only the global hooks are run
global_before_scenario(1)
global_before_each(2)
bar(3) # let's say foo(3) returns 4
global_after_each(4)
global_before_each(2)
bar(3) # let's say foo(3) returns 4
global_after_each(4)
# ... this block is repeated as many times as benchee has time
global_after_scenario(2)
suite_tear_down
```
### More verbose usage
It is important to note that the benchmarking code shown in the beginning is the convenience interface. The same benchmark in its more verbose form looks like this:
```elixir
list = Enum.to_list(1..10_000)
map_fun = fn i -> [i, i * i] end
[time: 3]
|> Benchee.init()
|> Benchee.system()
|> Benchee.benchmark("flat_map", fn -> Enum.flat_map(list, map_fun) end)
|> Benchee.benchmark(
"map.flatten",
fn -> list |> Enum.map(map_fun) |> List.flatten() end
)
|> Benchee.collect()
|> Benchee.statistics()
|> Benchee.relative_statistics()
|> Benchee.Formatter.output(Benchee.Formatters.Console)
# Instead of the last call you could also just use Benchee.Formatter.output()
# to just output all configured formatters
```
This is a take on the _functional transformation_ of data applied to benchmarks:
1. Configure the benchmarking suite to be run
2. Gather System data
3. Define the functions to be benchmarked
4. Run benchmarks with the given configuration gathering raw run times per function
5. Calculate statistics based on the raw run times
6. Calculate statistics between the scenarios (faster/slower...)
7. Format the statistics in a suitable way and print them out
This is also part of the **official API** and allows for more **fine grained control**. (It's also what benchee does internally when you use `Benchee.run/2`).
Do you just want to have all the raw run times? Just work with the result of `Benchee.collect/1`! Just want to have the calculated statistics and use your own formatting? Grab the result of `Benchee.statistics/1`! Or, maybe you want to write to a file or send an HTTP post to some online service? Just grab the complete suite after statistics were generated.
It also allows you to alter behaviour, normally `Benchee.load/1` is called right before the formatters so that neither the benchmarks are run again or statistics are computed again. However, you might want to run the benchmarks again or recompute the statistics. Then you can call `Benchee.load/1` right at the start.
This way Benchee should be flexible enough to suit your needs and be extended at will. Have a look at the [available plugins](#plugins).
### Usage from Erlang
Before you dig deep into this, it is inherently easier to setup a small elixir project, add a dependency to your erlang project and then run the benchmarks from elixir. The reason is easy - mix knows about rebar3 and knows how to work with it. The reverse isn't true so the road ahead is somewhat bumpy.
There is an [example project](https://github.com/PragTob/benchee_erlang_try) to check out.
You can use the [rebar3_elixir_compile](https://github.com/barrel-db/rebar3_elixir_compile) plugin. In your `rebar.config` you can do the following which should get you started:
```erlang
deps, [
{benchee, {elixir, "benchee", "0.9.0"}}
]}.
{plugins, [
{ rebar3_elixir_compile, ".*", {git, "https://github.com/barrel-db/rebar3_elixir_compile.git", {branch, "master"}}}
]}.
{provider_hooks, [
{pre, [{compile, {ex, compile}}]},
{pre, [{release, {ex, compile}}]}
]}.
{elixir_opts,
[
{env, dev}
]
}.
```
Then benchee already provides a `:benchee` interface for erlang compatibility which you can use. Sadly couldn't get it to work in an escript yet.
You can then invoke it like this (for instance):
```
tobi@comfy ~/github/benchee_erlang_try $ rebar3 shell
===> dependencies etc.
Erlang/OTP 18 [erts-7.3] [source] [64-bit] [smp:4:4] [async-threads:0] [hipe] [kernel-poll:false]
Eshell V7.3 (abort with ^G)
1> benchee:run(#{myFunc => fun() -> lists:sort([8, 2, 3, 4, 2, 1, 3, 4, 9, 10, 11, 12, 13, 20, 1000, -4, -5]) end}, [{warmup, 0}, {time, 2}]).
Operating System: Linux
CPU Information: Intel(R) Core(TM) i5-7200U CPU @ 2.50GHz
Number of Available Cores: 4
Available memory: 8.05 GB
Elixir 1.3.4
Erlang 18.3
Benchmark suite executing with the following configuration:
warmup: 0.0 μs
time: 2 s
parallel: 1
inputs: none specified
Estimated total run time: 2 s
Benchmarking myFunc...
Name ips average deviation median
myFunc 289.71 K 3.45 μs ±250.31% 3 μs
```
This doesn't seem to be too reliable right now, so suggestions and input are very welcome :)
## Plugins
Benchee only has small runtime dependencies that were initially extracted from it. Further functionality is provided through plugins that then pull in dependencies, such as HTML generation and CSV export. They help provide excellent visualization or interoperability.
* [benchee_html](//github.com/PragTob/benchee_html) - generate HTML including a data table and many different graphs with the possibility to export individual graphs as PNG :)
* [benchee_csv](//github.com/PragTob/benchee_csv) - generate CSV from your benchee benchmark results so you can import them into your favorite spreadsheet tool and make fancy graphs
* [benchee_json](//github.com/PragTob/benchee_json) - export suite results as JSON to feed anywhere or feed it to your JavaScript and make magic happen :)
* [benchee_markdown](//github.com/hrzndhrn/benchee_markdown) - write markdown files containing your benchmarking results
With the HTML plugin for instance you can get fancy graphs like this boxplot:
Of course there also are normal bar charts including standard deviation:
## Contributing [](https://www.codetriage.com/pragtob/benchee)
Contributions to benchee are **very welcome**! Bug reports, documentation, spelling corrections, whole features, feature ideas, bugfixes, new plugins, fancy graphics... all of those (and probably more) are much appreciated contributions!
Keep in mind that the [plugins](#plugins) live in their own repositories with their own issue tracker and they also like to get contributions :)
Please respect the [Code of Conduct](//github.com/bencheeorg/benchee/blob/master/CODE_OF_CONDUCT.md).
In addition to contributing code, you can help to triage issues. This can include reproducing bug reports, or asking for vital information such as version numbers or reproduction instructions. If you would like to start triaging issues, one easy way to get started is to [subscribe to pragtob/benchee on CodeTriage](https://www.codetriage.com/pragtob/benchee).
You can also look directly at the [open issues](https://github.com/bencheeorg/benchee/issues). There are `help wanted` and `good first issue` labels - those are meant as guidance, of course other issues can be tackled :)
A couple of (hopefully) helpful points:
* Feel free to ask for help and guidance on an issue/PR ("How can I implement this?", "How could I test this?", ...)
* Feel free to open early/not yet complete pull requests to get some early feedback
* When in doubt if something is a good idea open an issue first to discuss it
* In case I don't respond feel free to bump the issue/PR or ping me in other places
If you're on the [elixir-lang slack](https://elixir-lang.slack.com) also feel free to drop by in `#benchee` and say hi!
## Development
* `mix deps.get` to install dependencies
* `mix test` to run tests
* `mix dialyzer` to run dialyzer for type checking, might take a while on the first invocation (try building plts first with `mix dialyzer --plt`)
* `mix credo --strict` to find code style problems
* or run `mix guard` to run all of them continuously on file change
