Add new columns tracking when we partial-joined

changelog.d/13892.feature

@@ -0,0 +1 @@
+Faster remote room joins: record _when_ we first partial-join to a room.

synapse/handlers/federation.py

@@ -581,7 +581,11 @@ async def do_invite_join(
                 # Mark the room as having partial state.
                 # The background process is responsible for unmarking this flag,
                 # even if the join fails.
-                await self.store.store_partial_state_room(room_id, ret.servers_in_room)
+                await self.store.store_partial_state_room(
+                    room_id=room_id,
+                    servers=ret.servers_in_room,
+                    device_lists_stream_id=self.store.get_device_stream_token(),
+                )
 
             try:
                 max_stream_id = (
@@ -606,6 +610,14 @@ async def do_invite_join(
                     room_id,
                 )
                 raise LimitExceededError(msg=e.msg, errcode=e.errcode, retry_after_ms=0)
+            else:
+                # Record the join event id for future use (when we finish the full
+                # join). We have to do this after persisting the event to keep foreign
+                # key constraints intact.
+                if ret.partial_state:
+                    await self.store.write_partial_state_rooms_join_event_id(
+                        room_id, event.event_id
+                    )
             finally:
                 # Always kick off the background process that asynchronously fetches
                 # state for the room.

synapse/storage/databases/main/room.py

@@ -1777,28 +1777,46 @@ async def store_partial_state_room(
         self,
         room_id: str,
         servers: Collection[str],
+        device_lists_stream_id: int,
     ) -> None:
-        """Mark the given room as containing events with partial state
+        """Mark the given room as containing events with partial state.
+
+        We also store additional data that describes _when_ we first partial-joined this
+        room, which helps us to keep other homeservers in sync when we finally fully
+        join this room.
+
+        We do not include a `join_event_id` here---we need to wait for the join event
+        to be persisted first.
 
         Args:
             room_id: the ID of the room
             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.
         """
         await self.db_pool.runInteraction(
             "store_partial_state_room",
             self._store_partial_state_room_txn,
             room_id,
             servers,
+            device_lists_stream_id,
         )
 
     def _store_partial_state_room_txn(
-        self, txn: LoggingTransaction, room_id: str, servers: Collection[str]
+        self,
+        txn: LoggingTransaction,
+        room_id: str,
+        servers: Collection[str],
+        device_lists_stream_id: int,
     ) -> None:
         DatabasePool.simple_insert_txn(
             txn,
             table="partial_state_rooms",
             values={
                 "room_id": room_id,
+                "device_lists_stream_id": device_lists_stream_id,
+                # To be updated later once the join event is persisted.
+                "join_event_id": None,
             },
         )
         DatabasePool.simple_insert_many_txn(
@@ -1809,6 +1827,36 @@ def _store_partial_state_room_txn(
         )
         self._invalidate_cache_and_stream(txn, self.is_partial_state_room, (room_id,))
 
+    async def write_partial_state_rooms_join_event_id(
+        self,
+        room_id: str,
+        join_event_id: str,
+    ) -> None:
+        """Record the join event which resulted from a partial join.
+
+        We do this separately to `store_partial_state_room` because we need to wait for
+        the join event to be persisted. Otherwise we violate a foreign key constraint.
+        """
+        await self.db_pool.runInteraction(
+            "write_partial_state_rooms_join_event_id",
+            self._write_partial_state_rooms_join_event_id,
+            room_id,
+            join_event_id,
+        )
+
+    def _write_partial_state_rooms_join_event_id(
+        self,
+        txn: LoggingTransaction,
+        room_id: str,
+        join_event_id: str,
+    ) -> None:
+        DatabasePool.simple_update_txn(
+            txn,
+            table="partial_state_rooms",
+            keyvalues={"room_id": room_id},
+            updatevalues={"join_event_id": join_event_id},
+        )
+
     async def maybe_store_room_on_outlier_membership(
         self, room_id: str, room_version: RoomVersion
     ) -> None:

synapse/storage/schema/main/delta/73/04partial_join_details.sql

@@ -0,0 +1,23 @@
+/* Copyright 2022 The Matrix.org Foundation C.I.C
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+-- To ensure we correctly notify other homeservers about device list changes from our
+-- users after a partial join transitions to a full join, we need to know when we began
+-- the partial join. For now it's sufficient to know the device_list stream_id at the
+-- time of the partial join, and the join event created for us during a partial join.
+--
+-- Both columns are backwards compatible.
+ALTER TABLE partial_state_rooms ADD COLUMN device_lists_stream_id BIGINT NOT NULL DEFAULT 0;
+ALTER TABLE partial_state_rooms ADD COLUMN join_event_id TEXT REFERENCES events(event_id);