static-metric

prometheus-static-metric

Utility macro to build static metrics for the rust-prometheus library.

Why?

MetricVec (i.e. CounterVec, GaugeVec or HistogramVec) is slow. However if every possible values for labels are known, each metric in the MetricVec can be cached to avoid the runtime cost.

For example, the following code can be slow when it is invoked multiple times:

some_counter_vec.with_label_values(&["label_1_foo", "label_2_bar"]).inc();

It is because we are retriving a specific Counter according to values each time and to ensure thread-safety there is a lock inside which makes things worse.

We can optimize it by caching the counter by label values:

// init before hand
let foo_bar_counter = some_counter.with_label_values(&["label_1_foo", "label_2_bar"]);

foo_bar_counter.inc();

So far everything seems good. We achieve the same performance as Counter for CounterVec. But what if there are many labels and each of them has many values? We need to hand-craft a lot of code in this way.

That's what this crate solves. This crate provides a macro that helps you do the optimization above without really introducing a lot of templating code.

Getting Started

• Add to Cargo.toml:

  [dependencies]
  prometheus-static-metric = "0.1"

• Add to lib.rs:

  #![feature(proc_macro)]
  
  extern crate prometheus_static_metric;

Example

Use the make_static_metric! to define all possible values for each label. Your definition will be expanded to a real struct for easy access while keeping high-performance.

use prometheus_static_metric::make_static_metric;

make_static_metric! {
    pub struct MyStaticCounterVec: Counter {
        "method" => {
            post,
            get,
            put,
            delete,
        },
        "product" => {
            foo,
            bar,
        },
    }
}

fn main() {
    let vec = CounterVec::new(Opts::new("foo", "bar"), &["method", "product"]).unwrap();
    let static_counter_vec = MyStaticCounterVec::from(&vec);

    static_counter_vec.post.foo.inc();
    static_counter_vec.delete.bar.inc_by(4.0);
    assert_eq!(static_counter_vec.post.bar.get(), 0.0);
    assert_eq!(vec.with_label_values(&["post", "foo"]).get(), 1.0);
    assert_eq!(vec.with_label_values(&["delete", "bar"]).get(), 4.0);
}

Please take a look at examples directory for more.