Do not set default value for result_backend

lib/galaxy/config/__init__.py

@@ -1207,14 +1207,10 @@ class GalaxyAppConfiguration(BaseAppConfiguration, CommonConfigurationMixin):
             _load_theme(self.themes_config_file, self.themes)
 
     def _process_celery_config(self):
-        if self.celery_conf:
-            result_backend = self.celery_conf.get("result_backend")
-            if result_backend:
-                # If the result_backend is the default SQLite database, we need to
-                # ensure that the correct data directory is used.
-                if "results.sqlite" in result_backend:
-                    result_backend = f"db+sqlite:///{self._in_data_dir('results.sqlite')}?isolation_level=IMMEDIATE"
-                self.celery_conf["result_backend"] = result_backend
+        if self.celery_conf and self.celery_conf.get("result_backend") is None:
+            # If the result_backend is not set, use a SQLite database in the data directory
+            result_backend = f"db+sqlite:///{self._in_data_dir('results.sqlite')}?isolation_level=IMMEDIATE"
+            self.celery_conf["result_backend"] = result_backend
 
     def _check_database_connection_strings(self):
         """

lib/galaxy/config/schemas/config_schema.yml

@@ -3772,7 +3772,6 @@ mapping:
         type: any
         required: false
         default:
-          result_backend: db+sqlite:///./database/results.sqlite?isolation_level=IMMEDIATE
           task_routes:
             'galaxy.fetch_data': 'galaxy.external'
             'galaxy.set_job_metadata': 'galaxy.external'
@@ -3783,7 +3782,8 @@ mapping:
           of the task defined in the galaxy.celery.tasks module.
 
           The `broker_url` option, if unset, defaults to the value of `amqp_internal_connection`.
-          The `result_backend` option must be set if the `enable_celery_tasks` option is set.
+          The `result_backend` option, if unset, defaults to an SQLite database at '<data_dir>/results.sqlite'
+          for storing task results.
 
           The galaxy.fetch_data task can be disabled by setting its route to "disabled": `galaxy.fetch_data: disabled`.
           (Other tasks cannot be disabled on a per-task basis at this time.)