11 August 2014

wrk - a HTTP benchmarking tool

wrk is a modern HTTP benchmarking tool capable of generating significant load when run on a single multi-core CPU. It combines a multithreaded design with scalable event notification systems such as epoll and kqueue.

An optional LuaJIT script can perform HTTP request generation, response processing, and custom reporting. Several example scripts are located in scripts/

Basic Usage

wrk -t12 -c400 -d30s

This runs a benchmark for 30 seconds, using 12 threads, and keeping 400 HTTP connections open.


Running 30s test @ 12 threads and 400 connections Thread Stats Avg Stdev Max +/- Stdev Latency 635.91us 0.89ms 12.92ms 93.69% Req/Sec 56.20k 8.07k 62.00k 86.54% 22464657 requests in 30.00s, 17.76GB read Requests/sec: 748868.53 Transfer/sec: 606.33MB


wrk’s public Lua API is:

init     = function(args)
request  = function()
response = function(status, headers, body)
done     = function(summary, latency, requests)

wrk = {
  scheme  = "http",
  host    = "localhost",
  port    = nil,
  method  = "GET",
  path    = "/",
  headers = {},
  body    = nil

function wrk.format(method, path, headers, body)

  wrk.format returns a HTTP request string containing the passed
  parameters merged with values from the wrk table.

global init     -- function called when the thread is initialized
global request  -- function returning the HTTP message for each request
global response -- optional function called with HTTP response data
global done     -- optional function called with results of run

The init() function receives any extra command line arguments for the script. Script arguments must be separated from wrk arguments with “–” and scripts that override init() but not request() must call wrk.init()

The done() function receives a table containing result data, and two statistics objects representing the sampled per-request latency and per-thread request rate. Duration and latency are microsecond values and rate is measured in requests per second.

latency.min              -- minimum value seen
latency.max              -- maximum value seen
latency.mean             -- average value seen
latency.stdev            -- standard deviation
latency:percentile(99.0) -- 99th percentile value
latency[i]               -- raw sample value

summary = {
  duration = N,  -- run duration in microseconds
  requests = N,  -- total completed requests
  bytes    = N,  -- total bytes received
  errors   = {
    connect = N, -- total socket connection errors
    read    = N, -- total socket read errors
    write   = N, -- total socket write errors
    status  = N, -- total HTTP status codes > 399
    timeout = N  -- total request timeouts

Benchmarking Tips

The machine running wrk must have a sufficient number of ephemeral ports available and closed sockets should be recycled quickly. To handle the initial connection burst the server’s listen(2) backlog should be greater than the number of concurrent connections being tested.

A user script that only changes the HTTP method, path, adds headers or a body, will have no performance impact. If multiple HTTP requests are necessary they should be pre-generated and returned via a quick lookup in the request() call. Per-request actions, particularly building a new HTTP request, and use of response() will necessarily reduce the amount of load that can be generated.


wrk contains code from a number of open source projects including the ‘ae’ event loop from redis, the nginx/joyent/node.js ‘http-parser’, Mike Pall’s LuaJIT, and the Tiny Mersenne Twister PRNG. Please consult the NOTICE file for licensing details.

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