When restarting a partial join resync, prioritise the server which actioned a partial join (#14126)

synapse/storage/databases/main/room.py

@@ -97,6 +97,12 @@ class RoomSortOrder(Enum):
     STATE_EVENTS = "state_events"
 
 
+@attr.s(slots=True, frozen=True, auto_attribs=True)
+class PartialStateResyncInfo:
+    joined_via: Optional[str]
+    servers_in_room: List[str] = attr.ib(factory=list)
+
+
 class RoomWorkerStore(CacheInvalidationWorkerStore):
     def __init__(
         self,
@@ -1160,17 +1166,29 @@ class RoomWorkerStore(CacheInvalidationWorkerStore):
             desc="get_partial_state_servers_at_join",
         )
 
-    async def get_partial_state_rooms_and_servers(
+    async def get_partial_state_room_resync_info(
         self,
-    ) -> Mapping[str, Collection[str]]:
-        """Get all rooms containing events with partial state, and the servers known
-        to be in the room.
+    ) -> Mapping[str, PartialStateResyncInfo]:
+        """Get all rooms containing events with partial state, and the information
+        needed to restart a "resync" of those rooms.
 
         Returns:
             A dictionary of rooms with partial state, with room IDs as keys and
             lists of servers in rooms as values.
         """
-        room_servers: Dict[str, List[str]] = {}
+        room_servers: Dict[str, PartialStateResyncInfo] = {}
+
+        rows = await self.db_pool.simple_select_list(
+            table="partial_state_rooms",
+            keyvalues={},
+            retcols=("room_id", "joined_via"),
+            desc="get_server_which_served_partial_join",
+        )
+
+        for row in rows:
+            room_id = row["room_id"]
+            joined_via = row["joined_via"]
+            room_servers[room_id] = PartialStateResyncInfo(joined_via=joined_via)
 
         rows = await self.db_pool.simple_select_list(
             "partial_state_rooms_servers",
@@ -1182,7 +1200,15 @@ class RoomWorkerStore(CacheInvalidationWorkerStore):
         for row in rows:
             room_id = row["room_id"]
             server_name = row["server_name"]
-            room_servers.setdefault(room_id, []).append(server_name)
+            entry = room_servers.get(room_id)
+            if entry is None:
+                # There is a foreign key constraint which enforces that every room_id in
+                # partial_state_rooms_servers appears in partial_state_rooms. So we
+                # expect `entry` to be non-null. (This reasoning fails if we've
+                # partial-joined between the two SELECTs, but this is unlikely to happen
+                # in practice.)
+                continue
+            entry.servers_in_room.append(server_name)
 
         return room_servers
 
@@ -1827,6 +1853,7 @@ class RoomStore(RoomBackgroundUpdateStore, RoomWorkerStore):
         room_id: str,
         servers: Collection[str],
         device_lists_stream_id: int,
+        joined_via: str,
     ) -> None:
         """Mark the given room as containing events with partial state.
 
@@ -1842,6 +1869,7 @@ class RoomStore(RoomBackgroundUpdateStore, RoomWorkerStore):
             servers: other servers known to be in the room
             device_lists_stream_id: the device_lists stream ID at the time when we first
                 joined the room.
+            joined_via: the server name we requested a partial join from.
         """
         await self.db_pool.runInteraction(
             "store_partial_state_room",
@@ -1849,6 +1877,7 @@ class RoomStore(RoomBackgroundUpdateStore, RoomWorkerStore):
             room_id,
             servers,
             device_lists_stream_id,
+            joined_via,
         )
 
     def _store_partial_state_room_txn(
@@ -1857,6 +1886,7 @@ class RoomStore(RoomBackgroundUpdateStore, RoomWorkerStore):
         room_id: str,
         servers: Collection[str],
         device_lists_stream_id: int,
+        joined_via: str,
     ) -> None:
         DatabasePool.simple_insert_txn(
             txn,
@@ -1866,6 +1896,7 @@ class RoomStore(RoomBackgroundUpdateStore, RoomWorkerStore):
                 "device_lists_stream_id": device_lists_stream_id,
                 # To be updated later once the join event is persisted.
                 "join_event_id": None,
+                "joined_via": joined_via,
             },
         )
         DatabasePool.simple_insert_many_txn(