Data Segment API

[codebien]

This PR adds the primitives for accessing the execution segment info useful for data partitioning. It mostly adds the x/segment extension to the core.

This PR still lacks in terms of testing coverage, it's more a PoC PR for getting an agreement about the API and the use cases it should cover.

A basic example about how it's expected to be used:

// the essential part exported from the `samples/segmented-index.js` sample 
import { SharedSegmentedIndex } from 'k6/segment';

export default function () {
    let iterator = new SharedSegmentedIndex('myarr');
    let index = iterator.next();

    const reqBody = JSON.stringify(data[index.unscaled]);
    var res = http.post('https://httpbin.test.k6.io/anything', reqBody, params);
    check(res, { 'status 200': (r) => r.status === 200 });

    console.log(`Something: ${res.json().json.something}`)
}

running it with the following command:

k6 run -i 5 --execution-segment "0:1/2" --execution-segment-sequence "0,1/2,1" ./samples/segmented-index.js

the expected console output:

INFO[0001] Something: something else 1                   source=console
INFO[0001] Something: something else 3                   source=console
INFO[0001] Something: something else 5                   source=console
INFO[0001] Something: something else 7                   source=console
INFO[0002] Something: something else 9                   source=console

Questions

• Does it require a dedicated module? I think it could be directly part of k6/data.
• Do we expect the users will use both scaled and unscaled?
• GoTo is exported, how do we expect to use it?

[oleiade]

In the spirit of putting the review in context: I'd be keen to understand what's the use case/user scenario this addresses? Is there an issue giving some context opened somewhere? Cheers 😄

[codebien]

In the spirit of putting the review in context

Yep, sorry, I missed it in the description. It's a first iteration for #1539

[codebien]

Let's move back to Draft because after a discussion with @mstoykov we identified that this requires more discussion and API definition in the issue before starting reviewing it.

[codebien]

At the moment, this PR doesn't fit our expectations, so I'm closing it.