The k6/data module provides utilities for efficiently sharing data between VUs.
SharedArray
SharedArray is a read-only array that is shared between all VUs. It’s useful for sharing large datasets without duplicating them in memory for each VU.
Constructor
import { SharedArray } from 'k6/data';
const data = new SharedArray('my data', function () {
return JSON.parse(open('./data.json'));
});
Unique identifier for this shared array
Function that returns the array data. Called only once per test run. Must be synchronous.
Usage
SharedArray instances can be accessed like regular arrays:
import { SharedArray } from 'k6/data';
import { sleep } from 'k6';
const users = new SharedArray('users', function () {
return [
{ username: 'user1', password: 'pass1' },
{ username: 'user2', password: 'pass2' },
{ username: 'user3', password: 'pass3' },
];
});
export default function () {
// Access array elements
const user = users[0];
console.log(user.username);
// Get array length
console.log(users.length);
// Iterate over array
users.forEach((user) => {
console.log(user.username);
});
}
Examples
Loading Data from JSON File
import { SharedArray } from 'k6/data';
import http from 'k6/http';
const testData = new SharedArray('test data', function () {
return JSON.parse(open('./test-data.json'));
});
export default function () {
const randomData = testData[Math.floor(Math.random() * testData.length)];
http.post('https://test.k6.io/api', JSON.stringify(randomData));
}
Generating Test Data
import { SharedArray } from 'k6/data';
const data = new SharedArray('generated data', function () {
const generated = [];
for (let i = 0; i < 1000; i++) {
generated.push({
id: i,
name: `user-${i}`,
email: `user${i}@example.com`,
});
}
return generated;
});
export default function () {
console.log(data.length); // 1000
}
Per-VU Data Selection
import { SharedArray } from 'k6/data';
import exec from 'k6/execution';
const users = new SharedArray('all users', function () {
return JSON.parse(open('./users.json'));
});
export default function () {
// Each VU gets a different user based on its ID
const vuId = exec.vu.idInInstance - 1;
const user = users[vuId % users.length];
console.log(`VU ${vuId} using user ${user.username}`);
}
- Without SharedArray: Each VU has its own copy of the data in memory
- With SharedArray: Data is stored once and shared across all VUs
For example, with 1000 VUs and a 10MB dataset:
- Without SharedArray: ~10GB total memory usage
- With SharedArray: ~10MB total memory usage
Important Notes
SharedArray must be created in the init context (outside the default function).
The callback function must be synchronous. Async functions are not supported.
SharedArray is read-only. You cannot modify the data once created.
// ✅ Correct
import { SharedArray } from 'k6/data';
const data = new SharedArray('data', function () {
return [1, 2, 3];
});
export default function () {
console.log(data[0]); // OK
}
// ❌ Wrong - trying to modify
export default function () {
data[0] = 10; // This won't work
}