Add metrics tracking for eviction based on time to ResponseCache

synapse/util/caches/response_cache.py

@@ -36,7 +36,7 @@
 )
 from synapse.util import Clock
 from synapse.util.async_helpers import AbstractObservableDeferred, ObservableDeferred
-from synapse.util.caches import register_cache
+from synapse.util.caches import register_cache, EvictionReason
 
 logger = logging.getLogger(__name__)
 
@@ -167,7 +167,7 @@ def on_complete(r: RV) -> RV:
             # the should_cache bit, we leave it in the cache for now and schedule
             # its removal later.
             if self.timeout_sec and context.should_cache:
-                self.clock.call_later(self.timeout_sec, self.unset, key)
+                self.clock.call_later(self.timeout_sec, self.entry_timeout, key)
             else:
                 # otherwise, remove the result immediately.
                 self.unset(key)
@@ -187,6 +187,16 @@ def unset(self, key: KV) -> None:
         """
         self._result_cache.pop(key, None)
 
+    def evict_because(self, key: KV, reason: EvictionReason) -> None:
+        """Basically the same as unset, but update reason why evicting for metrics"""
+        self._metrics.inc_evictions(reason)
+        self.unset(key)
+
+    def entry_timeout(self, key: KV) -> None:
+        """For the all later to remove from the cache"""
+        logger.debug(f"Expiring from [{self._name}] - {key}")
+        self.evict_because(key, EvictionReason.time)
+
     async def wrap(
         self,
         key: KV,