fix(metrics): use f64::MAX as histogram bound to display +Inf properly (

#16701)

* use f64::MAX as histogram bound

* add test

src/common/base/src/runtime/metrics/registry.rs

@@ -43,8 +43,8 @@ use crate::runtime::metrics::process_collector::ProcessCollector;
 use crate::runtime::metrics::sample::MetricSample;
 use crate::runtime::ThreadTracker;
 
-pub const MIN_HISTOGRAM_BOUND: f64 = i64::MIN as f64;
-pub const MAX_HISTOGRAM_BOUND: f64 = i64::MAX as f64;
+pub const MIN_HISTOGRAM_BOUND: f64 = f64::MIN;
+pub const MAX_HISTOGRAM_BOUND: f64 = f64::MAX;
 
 pub static GLOBAL_METRICS_REGISTRY: LazyLock<GlobalRegistry> =
     LazyLock::new(GlobalRegistry::create);

src/common/base/tests/it/metrics/registry.rs

@@ -261,6 +261,19 @@ fn test_tracking_scoped_histogram_in_milliseconds_metrics() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn test_tracking_histogram_inf() -> Result<()> {
+    let uniq_metric_name = GlobalUniqName::unique();
+    let histogram = register_histogram_in_seconds(&uniq_metric_name);
+    // observe a value that exceed the max bucket of the histogram
+    histogram.observe(3600.0 * 355.0);
+
+    let output = GLOBAL_METRICS_REGISTRY.render_metrics()?;
+    let expected = format!("{}_bucket{{le=\"+Inf\"}} 1", uniq_metric_name);
+    assert!(output.contains(&expected));
+    Ok(())
+}
+
 #[test]
 fn test_tracking_scoped_family_counter_metrics() -> Result<()> {
     let uniq_metric_name = GlobalUniqName::unique();