Add metrics on cache eviction_listener

limitador/src/storage/redis/counters_cache.rs

@@ -4,6 +4,7 @@ use crate::storage::redis::DEFAULT_MAX_CACHED_COUNTERS;
 use dashmap::mapref::entry::Entry;
 use dashmap::DashMap;
 use metrics::{gauge, histogram};
+use moka::notification::RemovalCause;
 use moka::sync::Cache;
 use std::collections::HashMap;
 use std::future::Future;
@@ -309,9 +310,23 @@ impl CountersCacheBuilder {
         self
     }
 
+    fn eviction_listener(
+        _key: Arc<Counter>,
+        value: Arc<CachedCounterValue>,
+        _removal_cause: RemovalCause,
+    ) {
+        gauge!("cache_size").decrement(1);
+        if let Ok(writes) = value.pending_writes() {
+            histogram!("evicted_pending_writes").record(writes as f64);
+        }
+    }
+
     pub fn build(&self, period: Duration) -> CountersCache {
         CountersCache {
-            cache: Cache::new(self.max_cached_counters as u64),
+            cache: Cache::builder()
+                .max_capacity(self.max_cached_counters as u64)
+                .eviction_listener(Self::eviction_listener)
+                .build(),
             batcher: Batcher::new(period),
         }
     }