Remove some redundant joins on event_edges.room_id

We've long passed the point where it's possible to have the same event_id in
different tables, so these join conditions are redundant: we can just join on
event_id.

event_edges is of non-trivial size, and the room_id column is wasteful, so
let's stop reading from it. In future, we can stop writing to it, and then drop
it.

synapse/storage/event_federation.py

@@ -114,9 +114,9 @@ def get_oldest_events_with_depth_in_room_txn(self, txn, room_id):
         sql = (
             "SELECT b.event_id, MAX(e.depth) FROM events as e"
             " INNER JOIN event_edges as g"
-            " ON g.event_id = e.event_id AND g.room_id = e.room_id"
+            " ON g.event_id = e.event_id"
             " INNER JOIN event_backward_extremities as b"
-            " ON g.prev_event_id = b.event_id AND g.room_id = b.room_id"
+            " ON g.prev_event_id = b.event_id"
             " WHERE b.room_id = ? AND g.is_state is ?"
             " GROUP BY b.event_id"
         )
@@ -330,8 +330,7 @@ def _get_backfill_events(self, txn, room_id, event_list, limit):
             "SELECT depth, prev_event_id FROM event_edges"
             " INNER JOIN events"
             " ON prev_event_id = events.event_id"
-            " AND event_edges.room_id = events.room_id"
-            " WHERE event_edges.room_id = ? AND event_edges.event_id = ?"
+            " WHERE event_edges.event_id = ?"
             " AND event_edges.is_state = ?"
             " LIMIT ?"
         )
@@ -365,7 +364,7 @@ def _get_backfill_events(self, txn, room_id, event_list, limit):
 
             txn.execute(
                 query,
-                (room_id, event_id, False, limit - len(event_results))
+                (event_id, False, limit - len(event_results))
             )
 
             for row in txn:
@@ -402,7 +401,7 @@ def _get_missing_events(self, txn, room_id, earliest_events, latest_events,
 
         query = (
             "SELECT prev_event_id FROM event_edges "
-            "WHERE room_id = ? AND event_id = ? AND is_state = ? "
+            "WHERE event_id = ? AND is_state = ? "
             "LIMIT ?"
         )
 
@@ -411,7 +410,7 @@ def _get_missing_events(self, txn, room_id, earliest_events, latest_events,
             for event_id in front:
                 txn.execute(
                     query,
-                    (room_id, event_id, False, limit - len(event_results))
+                    (event_id, False, limit - len(event_results))
                 )
 
                 for e_id, in txn:

synapse/storage/events.py

@@ -520,7 +520,6 @@ def _calculate_new_extremeties(self, room_id, event_contexts, latest_event_ids):
             iterable=list(new_latest_event_ids),
             retcols=["prev_event_id"],
             keyvalues={
-                "room_id": room_id,
                 "is_state": False,
             },
             desc="_calculate_new_extremeties",