perf: replace RwLock with SCC HashMap for lock-free metadata access

Author: palindrom615

Cargo.lock

@@ -71,6 +71,7 @@ radix_trie = { version = "0.2", default-features = false }
 rand = { version = "0.9", default-features = false, features = [ "thread_rng" ] }
 rand_xoshiro = { version = "0.7", default-features = false }
 ratatui = { version = "0.28", default-features = false }
+scc = { version = "2.1", default-features = false }
 sketches-ddsketch = { version = "0.3", default-features = false }
 thiserror = { version = "2", default-features = false }
 tokio = { version = "1", default-features = false, features = ["rt", "net", "time", "rt-multi-thread"] }

Cargo.toml

@@ -20,6 +20,7 @@ metrics = { version = "^0.24", path = "../metrics" }
 metrics-util = { version = "^0.20", path = "../metrics-util", default-features = false, features = ["registry"] }
 opentelemetry = { workspace = true, features = ["metrics"] }
 portable-atomic = { workspace = true, features = ["float", "critical-section"] }
+scc = { workspace = true }
 
 [dev-dependencies]
 opentelemetry_sdk = { workspace = true, features = ["metrics", "rt-tokio", "testing"] }

metrics-exporter-opentelemetry/Cargo.toml

@@ -53,11 +53,11 @@ impl Recorder for OpenTelemetryRecorder {
         _unit: Option<Unit>,
         _description: SharedString,
     ) {
-        self.metadata.add_description(_key_name, MetricKind::Counter, _unit, _description);
+        self.metadata.set_description(_key_name, MetricKind::Counter, _unit, _description);
     }
 
     fn describe_gauge(&self, _key_name: KeyName, _unit: Option<Unit>, _description: SharedString) {
-        self.metadata.add_description(_key_name, MetricKind::Gauge, _unit, _description);
+        self.metadata.set_description(_key_name, MetricKind::Gauge, _unit, _description);
     }
 
     fn describe_histogram(
@@ -66,7 +66,7 @@ impl Recorder for OpenTelemetryRecorder {
         _unit: Option<Unit>,
         _description: SharedString,
     ) {
-        self.metadata.add_description(_key_name, MetricKind::Histogram, _unit, _description);
+        self.metadata.set_description(_key_name, MetricKind::Histogram, _unit, _description);
     }
 
     fn register_counter(&self, key: &Key, _metadata: &metrics::Metadata<'_>) -> Counter {

metrics-exporter-opentelemetry/src/lib.rs

@@ -1,7 +1,7 @@
 use metrics::{KeyName, SharedString, Unit};
 use metrics_util::MetricKind;
-use std::collections::HashMap;
-use std::sync::{Arc, PoisonError, RwLock};
+use scc::HashMap;
+use std::sync::Arc;
 
 #[derive(Clone)]
 pub struct MetricDescription {
@@ -20,58 +20,44 @@ impl MetricDescription {
 }
 
 /// Stores all metric metadata including descriptions and histogram bounds
-#[derive(Default)]
+#[derive(Clone, Default)]
 pub struct MetricMetadata {
-    inner: Arc<RwLock<MetricMetadataInner>>,
-}
-
-#[derive(Default)]
-struct MetricMetadataInner {
-    descriptions: HashMap<(KeyName, MetricKind), MetricDescription>,
-    histogram_bounds: HashMap<KeyName, Vec<f64>>,
+    descriptions: Arc<HashMap<(KeyName, MetricKind), MetricDescription>>,
+    histogram_bounds: Arc<HashMap<KeyName, Vec<f64>>>,
 }
 
 impl MetricMetadata {
     pub fn new() -> Self {
-        Self::default()
+        Self {
+            descriptions: Arc::new(HashMap::new()),
+            histogram_bounds: Arc::new(HashMap::new()),
+        }
     }
 
-    pub fn add_description(
+    pub fn set_description(
         &self,
         key_name: KeyName,
         metric_kind: MetricKind,
         unit: Option<Unit>,
         description: SharedString,
     ) {
         let new_entry = MetricDescription { unit, description };
-        let mut inner = self.inner.write().unwrap_or_else(PoisonError::into_inner);
-        inner.descriptions.insert((key_name, metric_kind), new_entry);
+        let _ = self.descriptions.insert((key_name, metric_kind), new_entry);
     }
 
     pub fn get_description(
         &self,
         key_name: &KeyName,
         metric_kind: MetricKind,
     ) -> Option<MetricDescription> {
-        let inner = self.inner.read().unwrap_or_else(PoisonError::into_inner);
-        inner.descriptions.get(&(key_name.clone(), metric_kind)).cloned()
+        self.descriptions.read(&(key_name.clone(), metric_kind), |_, v| v.clone())
     }
 
     pub fn set_histogram_bounds(&self, key_name: KeyName, bounds: Vec<f64>) {
-        let mut inner = self.inner.write().unwrap_or_else(PoisonError::into_inner);
-        inner.histogram_bounds.insert(key_name, bounds);
+        let _ = self.histogram_bounds.insert(key_name, bounds);
     }
 
     pub fn get_histogram_bounds(&self, key_name: &KeyName) -> Option<Vec<f64>> {
-        let inner = self.inner.read().unwrap_or_else(PoisonError::into_inner);
-        inner.histogram_bounds.get(key_name).cloned()
+        self.histogram_bounds.read(key_name, |_, v| v.clone())
     }
 }
-
-impl Clone for MetricMetadata {
-    fn clone(&self) -> Self {
-        Self {
-            inner: Arc::clone(&self.inner),
-        }
-    }
-}