Avoid extra db lookups

Since we're about to look up the events themselves anyway, we can skip the
extra db queries here.

synapse/storage/event_federation.py

@@ -295,35 +295,6 @@ class EventFederationWorkerStore(EventsWorkerStore, SignatureWorkerStore,
             get_forward_extremeties_for_room_txn
         )
 
-    def get_room_ids_for_events(self, event_ids):
-        """Get a list of room IDs for which the given events belong.
-
-        Args:
-            event_ids (list): the events to look up the room of
-
-        Returns:
-            list, the room IDs for the events
-        """
-        return self.runInteraction(
-            "get_room_ids_for_events",
-            self._get_room_ids_for_events, event_ids
-        )
-
-    def _get_room_ids_for_events(self, txn, event_ids):
-        logger.debug("_get_room_ids_for_events: %s", repr(event_ids))
-
-        base_sql = (
-            "SELECT DISTINCT room_id FROM events"
-            " WHERE event_id IN (%s)"
-        )
-
-        txn.execute(
-            base_sql % (",".join(["?"] * len(event_ids)),),
-            event_ids
-        )
-
-        return [r[0] for r in txn]
-
     def get_backfill_events(self, room_id, event_list, limit):
         """Get a list of Events for a given topic that occurred before (and
         including) the events in event_list. Return a list of max size `limit`
@@ -372,6 +343,7 @@ class EventFederationWorkerStore(EventsWorkerStore, SignatureWorkerStore,
                 table="events",
                 keyvalues={
                     "event_id": event_id,
+                    "room_id": room_id,
                 },
                 retcol="depth",
                 allow_none=True,

synapse/storage/events_worker.py

@@ -19,7 +19,7 @@ from canonicaljson import json
 
 from twisted.internet import defer
 
-from synapse.api.errors import SynapseError
+from synapse.api.errors import NotFoundError
 # these are only included to make the type annotations work
 from synapse.events import EventBase  # noqa: F401
 from synapse.events import FrozenEvent
@@ -76,7 +76,7 @@ class EventsWorkerStore(SQLBaseStore):
     @defer.inlineCallbacks
     def get_event(self, event_id, check_redacted=True,
                   get_prev_content=False, allow_rejected=False,
-                  allow_none=False):
+                  allow_none=False, check_room_id=None):
         """Get an event from the database by event_id.
 
         Args:
@@ -87,7 +87,9 @@ class EventsWorkerStore(SQLBaseStore):
                 include the previous states content in the unsigned field.
             allow_rejected (bool): If True return rejected events.
             allow_none (bool): If True, return None if no event found, if
-                False throw an exception.
+                False throw a NotFoundError
+            check_room_id (str|None): if not None, check the room of the found event.
+                If there is a mismatch, behave as per allow_none.
 
         Returns:
             Deferred : A FrozenEvent.
@@ -99,10 +101,16 @@ class EventsWorkerStore(SQLBaseStore):
             allow_rejected=allow_rejected,
         )
 
-        if not events and not allow_none:
-            raise SynapseError(404, "Could not find event %s" % (event_id,))
+        event = events[0] if events else None
 
-        defer.returnValue(events[0] if events else None)
+        if event is not None and check_room_id is not None:
+            if event.room_id != check_room_id:
+                event = None
+
+        if event is None and not allow_none:
+            raise NotFoundError("Could not find event %s" % (event_id,))
+
+        defer.returnValue(event)
 
     @defer.inlineCallbacks
     def get_events(self, event_ids, check_redacted=True,