0.35.4

src/cache/collapse.rs

@@ -126,10 +126,19 @@ impl Cache {
             .uncacheable_until
             .lock()
             .unwrap_or_else(|e| e.into_inner());
-        if memo.len() >= UNCACHEABLE_MEMO_CAPACITY {
+        if memo.len() >= UNCACHEABLE_MEMO_CAPACITY && !memo.contains_key(&ticket.key) {
             memo.retain(|_, until| *until > now);
             if memo.len() >= UNCACHEABLE_MEMO_CAPACITY {
-                return;
+                // Keep hit-for-miss working for new keys under sustained churn:
+                // drop the marker closest to expiry instead of silently
+                // re-enabling request collapsing for this (uncacheable) key.
+                if let Some(oldest) = memo
+                    .iter()
+                    .min_by_key(|(_, until)| **until)
+                    .map(|(key, _)| *key)
+                {
+                    memo.remove(&oldest);
+                }
             }
         }
         memo.insert(ticket.key, now + UNCACHEABLE_MEMO_TTL);