2 files changed, 77 insertions, 2 deletions
diff --git a/synapse/storage/databases/main/account_data.py b/synapse/storage/databases/main/account_data.py
index 3e2c3191c8..0df12e6380 100644
--- a/synapse/storage/databases/main/account_data.py
+++ b/synapse/storage/databases/main/account_data.py
@@ -35,6 +35,7 @@ from synapse.storage.database import (
     LoggingTransaction,
 )
 from synapse.storage.databases.main.cache import CacheInvalidationWorkerStore
+from synapse.storage.databases.main.devices import DeviceWorkerStore
 from synapse.storage.databases.main.push_rule import PushRulesWorkerStore
 from synapse.storage.engines import PostgresEngine
 from synapse.storage.util.id_generators import (
@@ -536,6 +537,17 @@ class AccountDataWorkerStore(PushRulesWorkerStore, CacheInvalidationWorkerStore)
                 # account data entry to delete in the first place.
                 return False
 
+            # Record that this account data was deleted along with the devices that
+            # have yet to see it. Once all devices have later seen the delete, we can
+            # fully purge the row from `room_account_data`.
+            self._add_entries_to_account_data_undelivered_deletes_txn(
+                txn,
+                stream_id=next_id,
+                account_data_type=account_data_type,
+                room_id=room_id,
+                user_id=user_id,
+            )
+
             return True
 
         async with self._account_data_id_gen.get_next() as next_id:
@@ -706,6 +718,17 @@ class AccountDataWorkerStore(PushRulesWorkerStore, CacheInvalidationWorkerStore)
                 # account data entry to delete in the first place.
                 return False
 
+            # Record that this account data was deleted along with the devices that
+            # have yet to see it. Once all devices have later seen the delete, we can
+            # fully purge the row from `account_data`.
+            self._add_entries_to_account_data_undelivered_deletes_txn(
+                txn,
+                stream_id=next_id,
+                account_data_type=account_data_type,
+                room_id=None,
+                user_id=user_id,
+            )
+
             # Ignored users get denormalized into a separate table as an optimisation.
             if account_data_type == AccountDataTypes.IGNORED_USER_LIST:
                 # If this method was called with the ignored users account data type, we
@@ -757,6 +780,47 @@ class AccountDataWorkerStore(PushRulesWorkerStore, CacheInvalidationWorkerStore)
 
         return self._account_data_id_gen.get_current_token()
 
+    def _add_entries_to_account_data_undelivered_deletes_txn(
+        self,
+        txn: LoggingTransaction,
+        stream_id: int,
+        account_data_type: str,
+        room_id: Optional[str],
+        user_id: str,
+    ) -> None:
+        """
+        Adds an entry per device of the given user to the
+        'account_data_undelivered_deletes' table, which tracks the devices that have
+        yet to be informed of a deleted entry in either the 'account_data' or
+        'room_account_data' tables.
+
+        Entries for hidden devices will not be created.
+
+        Args:
+            txn: The transaction that is handling the delete from (room)_account_data.
+            stream_id: The stream_id of the delete entry in the (room)_account_data table.
+            account_data_type: The type of {room,user} account data that was deleted.
+            room_id: The ID of the room if this refers to room account data, otherwise
+                this should be None.
+            user_id: The ID of the user this account data is related to.
+        """
+        # TODO: Is this too gross? :P
+        # Alternative is to duplicate the code in get_devices_by_user
+        user_device_dicts = DeviceWorkerStore.get_devices_by_user_txn(
+            txn, self.db_pool, user_id
+        )
+
+        # Create an entry in the deleted account data table for each device ID.
+        self.db_pool.simple_insert_many_txn(
+            txn,
+            table="account_data_undelivered_deletes",
+            keys=("stream_id", "type", "room_id", "user_id", "device_id"),
+            values=(
+                (stream_id, account_data_type, room_id, user_id, device_id)
+                for device_id in user_device_dicts.keys()
+            ),
+        )
+
     async def purge_account_data_for_user(self, user_id: str) -> None:
         """
         Removes ALL the account data for a user.
diff --git a/synapse/storage/databases/main/devices.py b/synapse/storage/databases/main/devices.py
index a5bb4d404e..1a867d1f3e 100644
--- a/synapse/storage/databases/main/devices.py
+++ b/synapse/storage/databases/main/devices.py
@@ -276,11 +276,22 @@ class DeviceWorkerStore(RoomMemberWorkerStore, EndToEndKeyWorkerStore):
             A mapping from device_id to a dict containing "device_id", "user_id"
             and "display_name" for each device.
         """
-        devices = await self.db_pool.simple_select_list(
+        return await self.db_pool.runInteraction(
+            "get_devices_by_user",
+            self.get_devices_by_user_txn,
+            self.db_pool,
+            user_id,
+        )
+
+    @staticmethod
+    def get_devices_by_user_txn(
+        txn: LoggingTransaction, db_pool: DatabasePool, user_id: str
+    ) -> Dict[str, Dict[str, str]]:
+        devices = db_pool.simple_select_list_txn(
+            txn,
             table="devices",
             keyvalues={"user_id": user_id, "hidden": False},
             retcols=("user_id", "device_id", "display_name"),
-            desc="get_devices_by_user",
         )
 
         return {d["device_id"]: d for d in devices}