Constant VUs

With the constant-vus executor, a fixed number of VUs execute as many iterations as possible for a specified amount of time.

For a shortcut to this executor, use the vus and duration options.

Options

Besides the common configuration options, this executor has the following options:

When to use

Use this executor if you need a specific number of VUs to run for a certain amount of time.

Example

This examples schedules 10 VUs to run constantly for a duration 30 seconds.

1import http from 'k6/http';
2import { sleep } from 'k6';
3
4export const options = {
5  discardResponseBodies: true,
6  scenarios: {
7    contacts: {
8      executor: 'constant-vus',
9      vus: 10,
10      duration: '30s',
11    },
12  },
13};
14
15export default function () {
16  http.get('https://test.k6.io/contacts.php');
17  // Injecting sleep
18  // Total iteration time is sleep + time to finish request.
19  sleep(0.5);
20}

Observations

The following graph depicts the performance of the example script:

Based upon our test scenario inputs and results:

• The number of VUs is fixed at 10, and are initialized before the test begins;
• Overall test duration is fixed at the configured 30 second duration;
• Each iteration of the default function is expected to be roughly 515ms, or ~2/s;
• Maximum throughput (highest efficiency) is therefore expected to be ~20 iters/s, 2 iters/s * 10 VUs;
• We see that the maximum throughput is reached and maintained for the majority of the test;
• Approximately 600 iterations are therefore performed in total, 30 seconds * 20 iters/s.