Lack of Beginner-Friendly Documentation for metrics_tracing_context

[artsiomkaltovich]

Hello,

First of all, thank you for your work on this project. I really appreciate it!

However, as a beginner, I’ve found it a bit difficult to understand how to use the metrics_tracing_context package.

The documentation starts with the following example:

use metrics_tracing_context::{MetricsLayer, TracingContextLayer};
use metrics_util::layers::Layer;
use tracing_subscriber::layer::SubscriberExt;

// Prepare tracing.
let subscriber = my_subscriber.with(MetricsLayer::new());
tracing::subscriber::set_global_default(subscriber).unwrap();

// Prepare metrics.
let recorder = TracingContextLayer::all().layer(my_recorder);
metrics::set_global_recorder(recorder).unwrap();

But I'm not quite sure what this is doing, or what my_subscriber refers to. Could it be addressed in the doc?

Also, is it possible to control which tracing fields are included as labels—either when registering metrics (e.g., with the register_gauge_vec macro) or when using methods like observe or inc?

I believe the documentation of this project could benefit from some improvements.

Thank you in advance for your help!

[tobz]

👋🏻

However, as a beginner, I’ve found it a bit difficult to understand how to use the metrics_tracing_context package.
...
I believe the documentation of this project could benefit from some improvements.

I agree that there could be some better documentation and examples on how to use metrics-tracing-context, and some of the other crates, as well. Unfortunately, I'm able to spend a limited amount of time supporting metrics these days, so the best I can do at the moment is reviewing PRs offering up those improvements.

Also, is it possible to control which tracing fields are included as labels—either when registering metrics (e.g., with the register_gauge_vec macro) or when using methods like observe or inc?

You'll want to look at TracingContextLayer::only_allow.

[artsiomkaltovich]

Hello @tobz

You'll want to look at TracingContextLayer::only_allow.

Just to confirm—do I understand correctly that this is a global setting that will be applied to all metrics?

I'm looking for a way to have different subsets of labels for different metrics, as well as to control which labels are added to logs. Some labels might be too large or verbose for logging purposes, so I'd like to manage that separately.

Is there a recommended approach for this?

Thank you!

Unfortunately, I'm able to spend a limited amount of time supporting metrics these days, so the best I can do at the moment is reviewing PRs offering up those improvements.

Unfortunately I am quite busy too and I am not sure I understand the package enough. I will look into it.

[tobz]

Just to confirm—do I understand correctly that this is a global setting that will be applied to all metrics?

It would apply the configured label filter to all metrics, yes.

I'm looking for a way to have different subsets of labels for different metrics, as well as to control which labels are added to logs. Some labels might be too large or verbose for logging purposes, so I'd like to manage that separately.

Is there a recommended approach for this?

You'd have to write a custom implementation of LabelFilter.

None of this has anything to do with the fields you choose to add to tracing spans, however.. just how the fields of the current span influence the labels of any emitted metric.

[artsiomkaltovich]

Hello @tobz.

I've created PR #583. Please review it when you have a time.

Regards.