Document ability to set a static concurrency for request.concurrency

[jszwedko]

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Problem

The documentation for request.concurrency doesn't indicate that you can set a static concurrency limit (a useful feature).

We should fix the docs to document how to set a static concurrency (like request.concurrency = 50).

Configuration

No response

Version

vector v0.32.1

Debug Output

No response

Example Data

No response

Additional Context

No response

References

• request.concurrency of none should mean "no concurrency" #18594
• request.concurrency default is incorrectly documented #18593

[jszwedko]

I think this is still an issue as we the changes to document a static concurrency were backed out of #18651

[neuronull]

This seems to be related to how the docs are generated from the code, and the fact that the fixed concurrency isn't actually represented in the enum.

Perhaps a way forward is to add an example to showcase the static usage, which we don't have right now.

We can also see if the auto generation of docs could be improved to handle this use case.

vector/src/sinks/util/service/concurrency.rs

Lines 24 to 37 in 30a1e26

	pub enum Concurrency {
	/// A fixed concurrency of 1.
	///
	/// Only one request can be outstanding at any given time.
	None,
	/// Concurrency is managed by the [Adaptive Request Concurrency][arc] feature.
	///
	/// [arc]: https://vector.dev/docs/about/under-the-hood/networking/arc/
	Adaptive,
	/// A fixed amount of concurrency is allowed.
	Fixed(usize),
	}