Change to not require a state_groups.room_id index.

This does mean that we won't clean up orphaned state groups (i.e. state
groups that were persisted but the associated event wasn't).

synapse/storage/data_stores/main/events.py

@@ -1624,7 +1624,10 @@ class EventsStore(
         """Deletes all record of a room
 
         Args:
-            room_id (str):
+            room_id (str)
+
+        Returns:
+            Deferred[List[int]]: The list of state groups to delete.
         """
 
         return self.runInteraction("purge_room", self._purge_room_txn, room_id)
@@ -1714,10 +1717,24 @@ class EventsStore(
         #       index on them. In any case we should be clearing out 'stream' tables
         #       periodically anyway (#5888)
 
+        # Now we fetch all the state groups that should be deleted.
+        txn.execute(
+            """
+                SELECT DISTINCT state_group FROM events
+                INNER JOIN event_to_state_groups USING(event_id)
+                WHERE events.room_id = ?
+            """,
+            (room_id,),
+        )
+
+        state_groups = [row[0] for row in txn]
+
         # TODO: we could probably usefully do a bunch of cache invalidation here
 
         logger.info("[purge] done")
 
+        return state_groups
+
     def purge_unreferenced_state_groups(
         self, room_id: str, state_groups_to_delete: Set[int]
     ) -> defer.Deferred:
@@ -1825,54 +1842,53 @@ class EventsStore(
 
         return {row["state_group"]: row["prev_state_group"] for row in rows}
 
-    def purge_room_state(self, room_id):
+    def purge_room_state(self, room_id, state_groups_to_delete):
         """Deletes all record of a room from state tables
 
         Args:
             room_id (str):
+            state_groups_to_delete (list[int]): State groups to delete
         """
 
         return self.runInteraction(
-            "purge_room_state", self._purge_room_state_txn, room_id
+            "purge_room_state",
+            self._purge_room_state_txn,
+            room_id,
+            state_groups_to_delete,
         )
 
-    def _purge_room_state_txn(self, txn, room_id):
+    def _purge_room_state_txn(self, txn, room_id, state_groups_to_delete):
         # first we have to delete the state groups states
         logger.info("[purge] removing %s from state_groups_state", room_id)
 
-        txn.execute(
-            """
-            DELETE FROM state_groups_state
-            WHERE state_group IN (
-                SELECT state_group FROM state_groups
-                WHERE room_id = ?
-            )
-            """,
-            (room_id,),
+        self._simple_delete_many_txn(
+            txn,
+            table="state_groups_state",
+            column="state_group",
+            iterable=state_groups_to_delete,
+            keyvalues={},
         )
 
         # ... and the state group edges
         logger.info("[purge] removing %s from state_group_edges", room_id)
 
-        txn.execute(
-            """
-            DELETE FROM state_group_edges
-            WHERE state_group IN (
-                SELECT state_group FROM state_groups
-                WHERE room_id = ?
-            )
-            """,
-            (room_id,),
+        self._simple_delete_many_txn(
+            txn,
+            table="state_group_edges",
+            column="state_group",
+            iterable=state_groups_to_delete,
+            keyvalues={},
         )
 
         # ... and the state groups
         logger.info("[purge] removing %s from state_groups", room_id)
 
-        txn.execute(
-            """
-            DELETE FROM state_groups WHERE room_id = ?
-            """,
-            (room_id,),
+        self._simple_delete_many_txn(
+            txn,
+            table="state_groups",
+            column="id",
+            iterable=state_groups_to_delete,
+            keyvalues={},
         )
 
     async def is_event_after(self, event_id1, event_id2):

synapse/storage/data_stores/main/schema/delta/56/state_group_room_idx.sql

@@ -1,17 +0,0 @@
-/* Copyright 2019 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.
- */
-
-INSERT INTO background_updates (update_name, progress_json) VALUES
-    ('state_groups_room_id_idx', '{}');

synapse/storage/data_stores/main/state.py

@@ -1023,7 +1023,6 @@ class StateBackgroundUpdateStore(
     STATE_GROUP_INDEX_UPDATE_NAME = "state_group_state_type_index"
     CURRENT_STATE_INDEX_UPDATE_NAME = "current_state_members_idx"
     EVENT_STATE_GROUP_INDEX_UPDATE_NAME = "event_to_state_groups_sg_index"
-    STATE_GROUPS_ROOM_INDEX_UPDATE_NAME = "state_groups_room_id_idx"
 
     def __init__(self, db_conn, hs):
         super(StateBackgroundUpdateStore, self).__init__(db_conn, hs)
@@ -1047,12 +1046,6 @@ class StateBackgroundUpdateStore(
             table="event_to_state_groups",
             columns=["state_group"],
         )
-        self.register_background_index_update(
-            self.STATE_GROUPS_ROOM_INDEX_UPDATE_NAME,
-            index_name="state_groups_room_id_idx",
-            table="state_groups",
-            columns=["room_id"],
-        )
 
     @defer.inlineCallbacks
     def _background_deduplicate_state(self, progress, batch_size):

synapse/storage/purge_events.py

@@ -33,8 +33,8 @@ class PurgeEventsStorage(object):
         """Deletes all record of a room
         """
 
-        yield self.stores.main.purge_room(room_id)
-        yield self.stores.main.purge_room_state(room_id)
+        state_groups_to_delete = yield self.stores.main.purge_room(room_id)
+        yield self.stores.main.purge_room_state(room_id, state_groups_to_delete)
 
     @defer.inlineCallbacks
     def purge_history(self, room_id, token, delete_local_events):