Add a background job to automatically delete stale devices (#12855)

Co-authored-by: Patrick Cloke <clokep@users.noreply.github.com>

synapse/storage/databases/main/devices.py

@@ -1154,6 +1154,45 @@ class DeviceWorkerStore(SQLBaseStore):
             _prune_txn,
         )
 
+    async def get_local_devices_not_accessed_since(
+        self, since_ms: int
+    ) -> Dict[str, List[str]]:
+        """Retrieves local devices that haven't been accessed since a given date.
+
+        Args:
+            since_ms: the timestamp to select on, every device with a last access date
+                from before that time is returned.
+
+        Returns:
+            A dictionary with an entry for each user with at least one device matching
+            the request, which value is a list of the device ID(s) for the corresponding
+            device(s).
+        """
+
+        def get_devices_not_accessed_since_txn(
+            txn: LoggingTransaction,
+        ) -> List[Dict[str, str]]:
+            sql = """
+                SELECT user_id, device_id
+                FROM devices WHERE last_seen < ? AND hidden = FALSE
+            """
+            txn.execute(sql, (since_ms,))
+            return self.db_pool.cursor_to_dict(txn)
+
+        rows = await self.db_pool.runInteraction(
+            "get_devices_not_accessed_since",
+            get_devices_not_accessed_since_txn,
+        )
+
+        devices: Dict[str, List[str]] = {}
+        for row in rows:
+            # Remote devices are never stale from our point of view.
+            if self.hs.is_mine_id(row["user_id"]):
+                user_devices = devices.setdefault(row["user_id"], [])
+                user_devices.append(row["device_id"])
+
+        return devices
+
 
 class DeviceBackgroundUpdateStore(SQLBaseStore):
     def __init__(