Shared state/memory between VUs

[robingustafsson]

We should evaluate possible ways to share larger blobs of data between VUs. The use case being that one might want to declare (or load from file on disk) a large data structure in the init context that is than used to parameterize data in the test.

Some ideas:

1. Share parts of the init context between VUs (not certain if this is at all doable in a clean way)
2. Create an API that is writable in the init context but only readable when running the test (executing the export default function())

An API for 2) could perhaps be something like:

import share from "k6/share";

// Parse data in to format specifc JS objects (CSV, JSON etc.)
let csvShare = share.load("./data.csv");
let jsonShare = share.load("./data.json");

export default function() {
    // Read data from the shared data blobs
    let row = csvShare.row();
    let randomRow = csvShare.random();
    let itemTitle = jsonShare.q("0.properties.title");
}

[Globegitter]

Is it possible to have any shared state at the moment? We are interested in sharing a counter between the requests, to know the how many number of requests it took until a certain condition a has been met.

[na--]

At the moment you can use a custom Counter metric (docs here and here) to track that at the end of the test, but there's no shared counter that you can use and check inside of the script, sorry. Depending on your use case, thresholds may be able to do the job, but if not, follow this issue for updates on any new shared state features.

[na--]

This was resolved by #1739. As described in the release notes (we don't quite have the docs updated yet), k6 now has a way for scripts to use a huge read-only array without the need to have a copy in every VU. We could do something similar for a map in the future, if needs be, but that would be a separate issue. And data segmentation (i.e. VUs independently iterating over non-overlapping elements of the array) falls under #1539. So, I think this can be closed 🎉