Remove useless async job to delete device messages on sync (#16491)

changelog.d/16491.misc

@@ -0,0 +1 @@
+Remove useless async job to delete device messages on sync, since we only deliver (and hence delete) up to 100 device messages at a time.

synapse/handlers/sync.py

@@ -40,7 +40,6 @@ from synapse.api.filtering import FilterCollection
 from synapse.api.presence import UserPresenceState
 from synapse.api.room_versions import KNOWN_ROOM_VERSIONS
 from synapse.events import EventBase
-from synapse.handlers.device import DELETE_DEVICE_MSGS_TASK_NAME
 from synapse.handlers.relations import BundledAggregations
 from synapse.logging import issue9533_logger
 from synapse.logging.context import current_context
@@ -363,36 +362,15 @@ class SyncHandler:
         # (since we now know that the device has received them)
         if since_token is not None:
             since_stream_id = since_token.to_device_key
-            # Fast path: delete a limited number of to-device messages up front.
-            # We do this to avoid the overhead of scheduling a task for every
-            # sync.
-            device_deletion_limit = 100
             deleted = await self.store.delete_messages_for_device(
                 sync_config.user.to_string(),
                 sync_config.device_id,
                 since_stream_id,
-                limit=device_deletion_limit,
             )
             logger.debug(
                 "Deleted %d to-device messages up to %d", deleted, since_stream_id
             )
 
-            # If we hit the limit, schedule a background task to delete the rest.
-            if deleted >= device_deletion_limit:
-                await self._task_scheduler.schedule_task(
-                    DELETE_DEVICE_MSGS_TASK_NAME,
-                    resource_id=sync_config.device_id,
-                    params={
-                        "user_id": sync_config.user.to_string(),
-                        "device_id": sync_config.device_id,
-                        "up_to_stream_id": since_stream_id,
-                    },
-                )
-                logger.debug(
-                    "Deletion of to-device messages up to %d scheduled",
-                    since_stream_id,
-                )
-
         if timeout == 0 or since_token is None or full_state:
             # we are going to return immediately, so don't bother calling
             # notifier.wait_for_events.

synapse/storage/databases/main/deviceinbox.py

@@ -450,7 +450,7 @@ class DeviceInboxWorkerStore(SQLBaseStore):
         user_id: str,
         device_id: Optional[str],
         up_to_stream_id: int,
-        limit: int,
+        limit: Optional[int] = None,
     ) -> int:
         """
         Args:
@@ -481,11 +481,12 @@ class DeviceInboxWorkerStore(SQLBaseStore):
         ROW_ID_NAME = self.database_engine.row_id_name
 
         def delete_messages_for_device_txn(txn: LoggingTransaction) -> int:
+            limit_statement = "" if limit is None else f"LIMIT {limit}"
             sql = f"""
                 DELETE FROM device_inbox WHERE {ROW_ID_NAME} IN (
                   SELECT {ROW_ID_NAME} FROM device_inbox
                   WHERE user_id = ? AND device_id = ? AND stream_id <= ?
-                  LIMIT {limit}
+                  {limit_statement}
                 )
                 """
             txn.execute(sql, (user_id, device_id, up_to_stream_id))