Shared iterations

The shared-iterations executor shares iterations between the number of VUs. The test ends once k6 executes all iterations.

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

note

Iterations are not guaranteed to be evenly distributed with this executor. VU that executes faster will complete more iterations than slower VUs.

To guarantee that every VU completes a specific, fixed number of iterations, use the per-VU iterations executor.

Options

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

When to use

This executor is suitable when you want a specific number of VUs to complete a fixed number of total iterations, and the amount of iterations per VU is unimportant. If the time to complete a number of test iterations is your concern, this executor should perform best.

An example use case is for quick performance tests in the development build cycle. As developers make changes, they might run the test against the local code to test for performance regressions. Thus the executor works well with a shift-left policy, where emphasizes testing performance early in the development cycle, when the cost of a fix is lowest.

Example

The following example schedules 200 total iterations shared by 10 VUs with a maximum test duration of 30 seconds.

1import http from 'k6/http';
2import { sleep } from 'k6';
3
4export const options = {
5  discardResponseBodies: true,
6  scenarios: {
7    contacts: {
8      executor: 'shared-iterations',
9      vus: 10,
10      iterations: 200,
11      maxDuration: '30s',
12    },
13  },
14};
15
16export default function () {
17  http.get('https://test.k6.io/contacts.php');
18  // Injecting sleep
19  // Sleep time is 500ms. Total iteration time is sleep + time to finish request.
20  sleep(0.5);
21}

Observations

The following graph depicts the performance of the example script:

Based upon our test scenario inputs and results:

• Test is limited to a fixed number of 200 iterations of the default function;
• The number of VUs is fixed to 10, and are initialized before the test begins;
• 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;
• The maximum throughput is maintained for a larger portion of the test;
• The distribution of iterations may be skewed: one VU may have performed 50 iterations, another only 10.