0.35.4

src/cache/lookup/hot.rs

@@ -43,7 +43,18 @@ impl Cache {
                 ticket.freshness_headers(),
             );
             if state.servable() {
-                let sequence = store.next_sequence();
+                // Approximate LRU: an entry already among the most recently used
+                // eighth of the store is not re-linked on every hit. This keeps the
+                // global HOT lock short for popular objects without changing which
+                // cold entries are evicted first.
+                let promote = store
+                    .entries
+                    .get(&storage_key)
+                    .is_some_and(|entry| {
+                        store.sequence.saturating_sub(entry.sequence)
+                            > (store.entries.len() as u64) / 8
+                    });
+                let sequence = if promote { store.next_sequence() } else { 0 };
                 let (
                     old_sequence,
                     headers,
@@ -59,7 +70,9 @@ impl Cache {
                     let old_sequence = entry.sequence;
                     entry.hits = entry.hits.saturating_add(1);
                     entry.last_access = Instant::now();
-                    entry.sequence = sequence;
+                    if promote {
+                        entry.sequence = sequence;
+                    }
                     (
                         old_sequence,
                         Arc::clone(&entry.headers),
@@ -72,8 +85,10 @@ impl Cache {
                         entry.body.len(),
                     )
                 };
-                store.lru.remove(&old_sequence);
-                store.lru.insert(sequence, storage_key);
+                if promote {
+                    store.lru.remove(&old_sequence);
+                    store.lru.insert(sequence, storage_key);
+                }
                 self.counters.hits.fetch_add(1, Ordering::Relaxed);
                 drop(store);
 
@@ -88,7 +103,7 @@ impl Cache {
                     response.extensions_mut().insert(crate::compression::Skip);
                 }
                 response.headers_mut().insert(::http::header::AGE,
-                    HeaderValue::from_str(&age.to_string()).expect("integer header"),
+                    HeaderValue::from(age),
                 );
                 self.domain_stats
                     .saved_body_hit(&ticket.scope, &ticket.domain, body_bytes);
@@ -285,7 +300,7 @@ impl Cache {
             response.extensions_mut().insert(crate::compression::Skip);
         }
         response.headers_mut().insert(::http::header::AGE,
-            HeaderValue::from_str(&age.to_string()).expect("integer header"),
+            HeaderValue::from(age),
         );
         self.domain_stats
             .saved_body_hit(&ticket.scope, &ticket.domain, entry.body_bytes);