Don't pull event from DB when handling replication traffic. (#8669)

I was trying to make it so that we didn't have to start a background task when handling RDATA, but that is a bigger job (due to all the code in `generic_worker`). However I still think not pulling the event from the DB may help reduce some DB usage due to replication, even if most workers will simply go and pull that event from the DB later anyway.

Co-authored-by: Patrick Cloke <clokep@users.noreply.github.com>

synapse/replication/tcp/client.py

@@ -141,21 +141,25 @@ class ReplicationDataHandler:
                 if row.type != EventsStreamEventRow.TypeId:
                     continue
                 assert isinstance(row, EventsStreamRow)
+                assert isinstance(row.data, EventsStreamEventRow)
 
-                event = await self.store.get_event(
-                    row.data.event_id, allow_rejected=True
-                )
-                if event.rejected_reason:
+                if row.data.rejected:
                     continue
 
                 extra_users = ()  # type: Tuple[UserID, ...]
-                if event.type == EventTypes.Member:
-                    extra_users = (UserID.from_string(event.state_key),)
+                if row.data.type == EventTypes.Member and row.data.state_key:
+                    extra_users = (UserID.from_string(row.data.state_key),)
 
                 max_token = self.store.get_room_max_token()
                 event_pos = PersistedEventPosition(instance_name, token)
-                self.notifier.on_new_room_event(
-                    event, event_pos, max_token, extra_users
+                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_type=row.data.type,
+                    state_key=row.data.state_key,
+                    membership=row.data.membership,
                 )
 
         # Notify any waiting deferreds. The list is ordered by position so we

synapse/replication/tcp/streams/events.py

@@ -15,12 +15,15 @@
 # limitations under the License.
 import heapq
 from collections.abc import Iterable
-from typing import List, Tuple, Type
+from typing import TYPE_CHECKING, List, Optional, Tuple, Type
 
 import attr
 
 from ._base import Stream, StreamUpdateResult, Token
 
+if TYPE_CHECKING:
+    from synapse.server import HomeServer
+
 """Handling of the 'events' replication stream
 
 This stream contains rows of various types. Each row therefore contains a 'type'
@@ -81,12 +84,14 @@ class BaseEventsStreamRow:
 class EventsStreamEventRow(BaseEventsStreamRow):
     TypeId = "ev"
 
-    event_id = attr.ib()  # str
-    room_id = attr.ib()  # str
-    type = attr.ib()  # str
-    state_key = attr.ib()  # str, optional
-    redacts = attr.ib()  # str, optional
-    relates_to = attr.ib()  # str, optional
+    event_id = attr.ib(type=str)
+    room_id = attr.ib(type=str)
+    type = attr.ib(type=str)
+    state_key = attr.ib(type=Optional[str])
+    redacts = attr.ib(type=Optional[str])
+    relates_to = attr.ib(type=Optional[str])
+    membership = attr.ib(type=Optional[str])
+    rejected = attr.ib(type=bool)
 
 
 @attr.s(slots=True, frozen=True)
@@ -113,7 +118,7 @@ class EventsStream(Stream):
 
     NAME = "events"
 
-    def __init__(self, hs):
+    def __init__(self, hs: "HomeServer"):
         self._store = hs.get_datastore()
         super().__init__(
             hs.get_instance_name(),