Constant arrival rate

Description

A fixed number of iterations are executed in a specified period of time. Since iteration execution time can vary because of test logic or the system-under-test responding more slowly, this executor will try to compensate by running a variable number of VUs—including potentially initializing more in the middle of the test—in order to meet the configured iteration rate. This approach is useful for a more accurate representation of RPS, for example.

See the arrival rate section for details.

Options

In addition to the common configuration options this executor also adds the following options:

When to use

When you want to maintain a constant number of requests without being affected by the performance of the system under test.

Examples

In this example, we'll execute a constant rate of 200 RPS for 1 minute, allowing k6 to dynamically schedule up to 100 VUs.

1import http from 'k6/http';
2
3export let options = {
4  discardResponseBodies: true,
5  scenarios: {
6    contacts: {
7      executor: 'constant-arrival-rate',
8      rate: 200, // 200 RPS, since timeUnit is the default 1s
9      duration: '1m',
10      preAllocatedVUs: 50,
11      maxVUs: 100,
12    },
13  },
14};
15
16export default function () {
17  http.get('https://test.k6.io/contacts.php');
18}

Note that in order to reliably achieve a fixed request rate, it's recommended to keep the function being executed very simple, with preferably only a single request call, and no additional processing or sleep() calls.