diff --git a/src/dflow/plugins/dispatcher.py b/src/dflow/plugins/dispatcher.py
index e04eb678..daa3ed6a 100644
--- a/src/dflow/plugins/dispatcher.py
+++ b/src/dflow/plugins/dispatcher.py
@@ -207,7 +207,7 @@ def __init__(self,
         self.resources_dict = {
             "number_node": 1,
             "cpu_per_node": 1,
-            "group_size": 5,
+            "group_size": 1,
             "envs": {
                 "DFLOW_WORKFLOW": "{{workflow.name}}",
                 "DFLOW_POD": "{{pod.name}}",
@@ -273,6 +273,12 @@ def render(self, template):
         merge = self.merge_sliced_step and hasattr(template, "slices") and\
             template.slices is not None
         if merge:
+            assert not template.slices.sub_path, "sub_path mode of slices "\
+                "is incompatible with merge_sliced_step"
+            assert template.slices.group_size is None, "group_size of slices "\
+                "is incompatible with merge_sliced_step"
+            assert template.slices.pool_size is None, "pool_size of slices "\
+                "is incompatible with merge_sliced_step"
             sliced_output_parameters = template.slices.output_parameter.copy()
             if "dflow_success_tag" in template.outputs.parameters:
                 sliced_output_parameters.append("dflow_success_tag")
@@ -435,6 +441,8 @@ def render(self, template):
                     "'./%s'), exist_ok=True)\n" % path
                 new_template.script += "    new_task_dict['backward_files']"\
                     ".append('./%s_' + str(i))\n" % path
+            new_template.script += "    new_task_dict['backward_files']"\
+                ".append('log')\n" # work around no Bohrium result file
             new_template.script += "    with open('script' + str(i), 'w')"\
                 " as f:\n"
             new_template.script += "        f.write(new_script)\n"
@@ -444,7 +452,6 @@ def render(self, template):
                 "'script' + str(i)\n"
             new_template.script += "    tasks.append(Task.load_from_dict("\
                 "new_task_dict))\n"
-            new_template.script += "resources.group_size = 1\n"
             new_template.script += "submission = Submission(work_base='.', "\
                 "machine=machine, resources=resources, task_list=tasks)\n"
         else:
diff --git a/src/dflow/step.py b/src/dflow/step.py
index e04269fb..b3e2c589 100644
--- a/src/dflow/step.py
+++ b/src/dflow/step.py
@@ -1294,6 +1294,7 @@ def render_by_executor(self, context=None):
                     InputParameter(value=None)
                 self.inputs.parameters["dflow_sequence_format"] = \
                     InputParameter(value="")
+                key = "0"
                 if self.with_param is not None:
                     self.inputs.parameters["dflow_with_param"].value = \
                         self.with_param
@@ -1313,9 +1314,11 @@ def render_by_executor(self, context=None):
                     self.inputs.parameters["dflow_sequence_format"].value = \
                         format
                     self.with_sequence = None
+                    if format is not None:
+                        key = format % 0
                 if self.key is not None:
                     self.inputs.parameters["dflow_key"] = InputParameter(
-                        value=str(self.key).replace("{{item}}", "merged"))
+                        value=str(self.key).replace("{{item}}", key))
         elif context is not None:
             self.template = context.render(self.template)