Merge pull request #2203 from matrix-org/erikj/event_cache_hit_ratio

Don't update event cache hit ratio from get_joined_users

2 files changed, 21 insertions, 2 deletions

diff --git a/synapse/storage/events.py b/synapse/storage/events.py
index 98707d40ee..2ab44ceaa7 100644
--- a/synapse/storage/events.py
+++ b/synapse/storage/events.py
@@ -1343,11 +1343,26 @@ class EventsStore(SQLBaseStore):
     def _invalidate_get_event_cache(self, event_id):
             self._get_event_cache.invalidate((event_id,))
 
-    def _get_events_from_cache(self, events, allow_rejected):
+    def _get_events_from_cache(self, events, allow_rejected, update_metrics=True):
+        """Fetch events from the caches
+
+        Args:
+            events (list(str)): list of event_ids to fetch
+            allow_rejected (bool): Whether to teturn events that were rejected
+            update_metrics (bool): Whether to update the cache hit ratio metrics
+
+        Returns:
+            dict of event_id -> _EventCacheEntry for each event_id in cache. If
+            allow_rejected is `False` then there will still be an entry but it
+            will be `None`
+        """
         event_map = {}
 
         for event_id in events:
-            ret = self._get_event_cache.get((event_id,), None)
+            ret = self._get_event_cache.get(
+                (event_id,), None,
+                update_metrics=update_metrics,
+            )
             if not ret:
                 continue
 
diff --git a/synapse/storage/roommember.py b/synapse/storage/roommember.py
index ad3c9b06d9..2fa20bd87c 100644
--- a/synapse/storage/roommember.py
+++ b/synapse/storage/roommember.py
@@ -421,9 +421,13 @@ class RoomMemberStore(SQLBaseStore):
         # We check if we have any of the member event ids in the event cache
         # before we ask the DB
 
+        # We don't update the event cache hit ratio as it completely throws off
+        # the hit ratio counts. After all, we don't populate the cache if we
+        # miss it here
         event_map = self._get_events_from_cache(
             member_event_ids,
             allow_rejected=False,
+            update_metrics=False,
         )
 
         missing_member_event_ids = []