examples/metrics-advanced: add explanation

Author: thomasstauffer666

examples/metrics-advanced/src/main.rs

@@ -34,6 +34,13 @@ fn init_meter_provider() -> opentelemetry_sdk::metrics::SdkMeterProvider {
     };
 
     // for example 3
+    // Unlike a regular OpenTelemetry histogram with fixed buckets, which can be
+    // specified explicitly, an exponential histogram calculates bucket widths
+    // automatically, growing them exponentially. The configuration is
+    // controlled by two parameters: max_size defines the maximum number of
+    // buckets, while max_scale adjusts the resolution, with higher values
+    // providing greater precision.
+    // https://opentelemetry.io/docs/specs/otel/metrics/data-model/#exponentialhistogram
     let my_view_change_aggregation = |i: &Instrument| {
         if i.name() == "my_third_histogram" {
             Stream::builder()
@@ -130,6 +137,9 @@ async fn main() -> Result<(), Box<dyn Error + Send + Sync + 'static>> {
     histogram2.record(1.8, &[KeyValue::new("mykey1", "v7")]);
 
     // Example 3 - Use exponential histogram.
+    // Internally the exponential histogram puts values either into a list of
+    // negative buckets or a set of positive buckets. Based on the values which
+    // are added the buckets are adjusted.
     let histogram3 = meter
         .f64_histogram("my_third_histogram")
         .with_description("My histogram example description")