Document the importance of sleep

[MattDodsonEnglish]

For developers who don't come from a testing background, the sleep() function can be confusing. Why waste CPU cycles doing nothing?

We have sleep recommendations in the browser recorder, a mention in the "high CPU" insight, and some mentions in k6-learn, but it'd be nice to have a more findable description, since sleep is in so many of our example scripts, and little "best practices" like this are some of the most requested docs.

[imiric]

We could just link to https://www.sleepfoundation.org/how-sleep-works/why-do-we-need-sleep

But to add something constructive: sleep() is very important to simulate actual user behavior. Users don't just hammer a web site like a bot would, and a lot of time is spent rendering and interacting with the frontend. Running a browser test represents that scenario better, and part of the use case for k6 is to stress the SUT and not behave exactly like a user would. But even in that case, sleep() is useful to pace the generated load, and not overload the load generator machine. Given that k6 is not strictly a load testing tool, but encompasses many different areas of observability, waiting for a specific amount of time is useful in other testing scenarios as well. So I agree that we should have a document to mention some of these examples.

[sniku]

I think the most important is to document that sleep() is a bad idea for arrival rate executors. At least, sleep should not be added at the end of the iteration, as we recommend for other executors.

[mstoykov]

On similar note ☝️ we likely should get something like delay for asynchronous code as sleep is blocking and synchronous.

[MattDodsonEnglish]

I think the most important is to document that sleep() is a bad idea for arrival rate executors. At least, sleep should not be added at the end of the iteration, as we recommend for other executors.

I just made a small note to account for this, if someone wants to review.

https://github.com/grafana/k6-docs/pull/1008/files

[ppcano]

Related -> Sleep pauses entire execution including websocket intervals