Batch up notifications after event persistence (#14033)

5 files changed, 66 insertions, 58 deletions

diff --git a/changelog.d/14033.misc b/changelog.d/14033.misc
new file mode 100644
index 0000000000..fe42852aa5
--- /dev/null
+++ b/changelog.d/14033.misc
@@ -0,0 +1 @@
+Don't repeatedly wake up the same users for batched events.
\ No newline at end of file
diff --git a/synapse/handlers/federation_event.py b/synapse/handlers/federation_event.py
index 778d8869b3..da319943cc 100644
--- a/synapse/handlers/federation_event.py
+++ b/synapse/handlers/federation_event.py
@@ -2240,8 +2240,8 @@ class FederationEventHandler:
         event_pos = PersistedEventPosition(
             self._instance_name, event.internal_metadata.stream_ordering
         )
-        await self._notifier.on_new_room_event(
-            event, event_pos, max_stream_token, extra_users=extra_users
+        await self._notifier.on_new_room_events(
+            [(event, event_pos)], max_stream_token, extra_users=extra_users
         )
 
         if event.type == EventTypes.Member and event.membership == Membership.JOIN:
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index 00e7645ba5..da1acea275 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -1872,6 +1872,7 @@ class EventCreationHandler:
             events_and_context, backfilled=backfilled
         )
 
+        events_and_pos = []
         for event in persisted_events:
             if self._ephemeral_events_enabled:
                 # If there's an expiry timestamp on the event, schedule its expiry.
@@ -1880,25 +1881,23 @@ class EventCreationHandler:
             stream_ordering = event.internal_metadata.stream_ordering
             assert stream_ordering is not None
             pos = PersistedEventPosition(self._instance_name, stream_ordering)
-
-            async def _notify() -> None:
-                try:
-                    await self.notifier.on_new_room_event(
-                        event, pos, max_stream_token, extra_users=extra_users
-                    )
-                except Exception:
-                    logger.exception(
-                        "Error notifying about new room event %s",
-                        event.event_id,
-                    )
-
-            run_in_background(_notify)
+            events_and_pos.append((event, pos))
 
             if event.type == EventTypes.Message:
                 # We don't want to block sending messages on any presence code. This
                 # matters as sometimes presence code can take a while.
                 run_in_background(self._bump_active_time, requester.user)
 
+        async def _notify() -> None:
+            try:
+                await self.notifier.on_new_room_events(
+                    events_and_pos, max_stream_token, extra_users=extra_users
+                )
+            except Exception:
+                logger.exception("Error notifying about new room events")
+
+        run_in_background(_notify)
+
         return persisted_events[-1]
 
     async def _maybe_kick_guest_users(
diff --git a/synapse/notifier.py b/synapse/notifier.py
index c42bb8266a..26b97cf766 100644
--- a/synapse/notifier.py
+++ b/synapse/notifier.py
@@ -294,35 +294,31 @@ class Notifier:
         """
         self._new_join_in_room_callbacks.append(cb)
 
-    async def on_new_room_event(
+    async def on_new_room_events(
         self,
-        event: EventBase,
-        event_pos: PersistedEventPosition,
+        events_and_pos: List[Tuple[EventBase, PersistedEventPosition]],
         max_room_stream_token: RoomStreamToken,
         extra_users: Optional[Collection[UserID]] = None,
     ) -> None:
-        """Unwraps event and calls `on_new_room_event_args`."""
-        await self.on_new_room_event_args(
-            event_pos=event_pos,
-            room_id=event.room_id,
-            event_id=event.event_id,
-            event_type=event.type,
-            state_key=event.get("state_key"),
-            membership=event.content.get("membership"),
-            max_room_stream_token=max_room_stream_token,
-            extra_users=extra_users or [],
-        )
+        """Creates a _PendingRoomEventEntry for each of the listed events and calls
+        notify_new_room_events with the results."""
+        event_entries = []
+        for event, pos in events_and_pos:
+            entry = self.create_pending_room_event_entry(
+                pos,
+                extra_users,
+                event.room_id,
+                event.type,
+                event.get("state_key"),
+                event.content.get("membership"),
+            )
+            event_entries.append((entry, event.event_id))
+        await self.notify_new_room_events(event_entries, max_room_stream_token)
 
-    async def on_new_room_event_args(
+    async def notify_new_room_events(
         self,
-        room_id: str,
-        event_id: str,
-        event_type: str,
-        state_key: Optional[str],
-        membership: Optional[str],
-        event_pos: PersistedEventPosition,
+        event_entries: List[Tuple[_PendingRoomEventEntry, str]],
         max_room_stream_token: RoomStreamToken,
-        extra_users: Optional[Collection[UserID]] = None,
     ) -> None:
         """Used by handlers to inform the notifier something has happened
         in the room, room event wise.
@@ -338,22 +334,33 @@ class Notifier:
         until all previous events have been persisted before notifying
         the client streams.
         """
-        self.pending_new_room_events.append(
-            _PendingRoomEventEntry(
-                event_pos=event_pos,
-                extra_users=extra_users or [],
-                room_id=room_id,
-                type=event_type,
-                state_key=state_key,
-                membership=membership,
-            )
-        )
-        self._notify_pending_new_room_events(max_room_stream_token)
+        for event_entry, event_id in event_entries:
+            self.pending_new_room_events.append(event_entry)
+            await self._third_party_rules.on_new_event(event_id)
 
-        await self._third_party_rules.on_new_event(event_id)
+        self._notify_pending_new_room_events(max_room_stream_token)
 
         self.notify_replication()
 
+    def create_pending_room_event_entry(
+        self,
+        event_pos: PersistedEventPosition,
+        extra_users: Optional[Collection[UserID]],
+        room_id: str,
+        event_type: str,
+        state_key: Optional[str],
+        membership: Optional[str],
+    ) -> _PendingRoomEventEntry:
+        """Creates and returns a _PendingRoomEventEntry"""
+        return _PendingRoomEventEntry(
+            event_pos=event_pos,
+            extra_users=extra_users or [],
+            room_id=room_id,
+            type=event_type,
+            state_key=state_key,
+            membership=membership,
+        )
+
     def _notify_pending_new_room_events(
         self, max_room_stream_token: RoomStreamToken
     ) -> None:
diff --git a/synapse/replication/tcp/client.py b/synapse/replication/tcp/client.py
index b2522f98ca..18252a2958 100644
--- a/synapse/replication/tcp/client.py
+++ b/synapse/replication/tcp/client.py
@@ -210,15 +210,16 @@ class ReplicationDataHandler:
 
                 max_token = self.store.get_room_max_token()
                 event_pos = PersistedEventPosition(instance_name, token)
-                await self.notifier.on_new_room_event_args(
-                    event_pos=event_pos,
-                    max_room_stream_token=max_token,
-                    extra_users=extra_users,
-                    room_id=row.data.room_id,
-                    event_id=row.data.event_id,
-                    event_type=row.data.type,
-                    state_key=row.data.state_key,
-                    membership=row.data.membership,
+                event_entry = self.notifier.create_pending_room_event_entry(
+                    event_pos,
+                    extra_users,
+                    row.data.room_id,
+                    row.data.type,
+                    row.data.state_key,
+                    row.data.membership,
+                )
+                await self.notifier.notify_new_room_events(
+                    [(event_entry, row.data.event_id)], max_token
                 )
 
                 # If this event is a join, make a note of it so we have an accurate