diff --git a/Makefile b/Makefile
index 15c38391e..2df576a7d 100644
--- a/Makefile
+++ b/Makefile
@@ -119,11 +119,11 @@ pre-commit:
 
 # Auto lint with black.
 auto-black:
-	$(PIPRUN) python -m black . --extend-exclude test/scripts --extend-exclude git_ignore_folder -l 120
+	$(PIPRUN) python -m black . --extend-exclude test/scripts --extend-exclude git_ignore_folder --extend-exclude .venv -l 120
 
 # Auto lint with isort.
 auto-isort:
-	$(PIPRUN) python -m isort . -s git_ignore_folder -s test/scripts
+	$(PIPRUN) python -m isort . -s git_ignore_folder -s test/scripts -s .venv
 
 # Auto lint with toml-sort.
 auto-toml-sort:
diff --git a/rdagent/log/utils/folder.py b/rdagent/log/utils/folder.py
index ea551223a..453fa2158 100644
--- a/rdagent/log/utils/folder.py
+++ b/rdagent/log/utils/folder.py
@@ -24,7 +24,7 @@ def get_first_session_file_after_duration(log_folder: str | Path, duration: str
             session_obj: LoopBase = pickle.load(f)
         timer = session_obj.timer
         all_duration = timer.all_duration
-        remain_time_duration = timer.remain_time_duration
+        remain_time_duration = timer.remain_time()
         if all_duration is None or remain_time_duration is None:
             msg = "Timer is not configured"
             raise ValueError(msg)
diff --git a/rdagent/scenarios/data_science/loop.py b/rdagent/scenarios/data_science/loop.py
index 49f0538d4..e02adbad5 100644
--- a/rdagent/scenarios/data_science/loop.py
+++ b/rdagent/scenarios/data_science/loop.py
@@ -228,19 +228,14 @@ def record(self, prev_out: dict[str, Any]):
             # set the local selection to the trace as global selection, then set the DAG parent for the trace
             if exp.local_selection is not None:
                 self.trace.set_current_selection(exp.local_selection)
-            self.trace.sync_dag_parent_and_hist()
-
-            self.trace.hist.append((exp, prev_out["feedback"]))
-
+            self.trace.sync_dag_parent_and_hist((exp, prev_out["feedback"]))
         else:
             exp: DSExperiment = prev_out["direct_exp_gen"] if isinstance(e, CoderError) else prev_out["coding"]
 
             # set the local selection to the trace as global selection, then set the DAG parent for the trace
             if exp.local_selection is not None:
                 self.trace.set_current_selection(exp.local_selection)
-            self.trace.sync_dag_parent_and_hist()
-
-            self.trace.hist.append(
+            self.trace.sync_dag_parent_and_hist(
                 (
                     exp,
                     ExperimentFeedback.from_exception(e),
diff --git a/rdagent/scenarios/data_science/proposal/exp_gen/base.py b/rdagent/scenarios/data_science/proposal/exp_gen/base.py
index b8d396c5c..046877ba5 100644
--- a/rdagent/scenarios/data_science/proposal/exp_gen/base.py
+++ b/rdagent/scenarios/data_science/proposal/exp_gen/base.py
@@ -3,6 +3,7 @@
 
 from rdagent.app.data_science.conf import DS_RD_SETTING
 from rdagent.core.evolving_framework import KnowledgeBase
+from rdagent.core.experiment import Experiment
 from rdagent.core.proposal import ExperimentFeedback, Hypothesis, Trace
 from rdagent.scenarios.data_science.experiment.experiment import COMPONENT, DSExperiment
 from rdagent.scenarios.data_science.scen import DataScienceScen
@@ -93,6 +94,7 @@ def get_leaves(self) -> list[int, ...]:
 
     def sync_dag_parent_and_hist(
         self,
+        exp_and_fb: tuple[Experiment, ExperimentFeedback],
     ) -> None:
         """
         Adding corresponding parent index to the dag_parent when the hist is going to be changed.
@@ -111,6 +113,7 @@ def sync_dag_parent_and_hist(
                 current_node_idx = len(self.hist) - 1
 
             self.dag_parent.append((current_node_idx,))
+        self.hist.append(exp_and_fb)
 
     def retrieve_search_list(
         self,
@@ -171,7 +174,7 @@ def has_component(
     def experiment_and_feedback_list_after_init(
         self,
         return_type: Literal["sota", "failed", "all"],
-        search_type: Literal["all", "ancestors"] = "all",
+        search_type: Literal["all", "ancestors"] = "ancestors",
         selection: tuple[int, ...] | None = None,
         max_retrieve_num: int | None = None,
     ) -> list[tuple[DSExperiment, ExperimentFeedback]]:
diff --git a/rdagent/scenarios/data_science/proposal/exp_gen/parallel.py b/rdagent/scenarios/data_science/proposal/exp_gen/parallel.py
index 6fb947cae..9d05c5ed2 100644
--- a/rdagent/scenarios/data_science/proposal/exp_gen/parallel.py
+++ b/rdagent/scenarios/data_science/proposal/exp_gen/parallel.py
@@ -38,8 +38,7 @@ def __init__(self, *args, **kwargs):
             "rdagent.scenarios.data_science.proposal.exp_gen.DSExpGen", self.scen
         )
         self.merge_exp_gen = ExpGen2Hypothesis(self.scen)
-        self.trace_scheduler: TraceScheduler = RoundRobinScheduler()
-        self.max_trace_num = DS_RD_SETTING.max_trace_num
+        self.trace_scheduler: TraceScheduler = RoundRobinScheduler(DS_RD_SETTING.max_trace_num)
 
     def gen(self, trace: "DSTrace") -> "Experiment":
         raise NotImplementedError(
@@ -69,15 +68,9 @@ async def async_gen(self, trace: DSTrace, loop: LoopBase) -> DSExperiment:
                     else:
                         # set the knowledge base option back to False for the other traces
                         DS_RD_SETTING.enable_knowledge_base = False
-                # step 1: select the parant trace to expand
-                # Policy: if we have fewer traces than our target, start a new one.
-                if trace.sub_trace_count < self.max_trace_num:
-                    local_selection = trace.NEW_ROOT
-                else:
-                    # Otherwise, use the scheduler to pick an existing trace to expand.
-                    local_selection = await self.trace_scheduler.select_trace(trace)
 
                 if loop.get_unfinished_loop_cnt(loop.loop_idx) < RD_AGENT_SETTINGS.get_max_parallel():
+                    local_selection = await self.trace_scheduler.next(trace)
 
                     # set the local selection as the global current selection for the trace
                     trace.set_current_selection(local_selection)
diff --git a/rdagent/scenarios/data_science/proposal/exp_gen/trace_scheduler.py b/rdagent/scenarios/data_science/proposal/exp_gen/trace_scheduler.py
index df4186727..b28be59a5 100644
--- a/rdagent/scenarios/data_science/proposal/exp_gen/trace_scheduler.py
+++ b/rdagent/scenarios/data_science/proposal/exp_gen/trace_scheduler.py
@@ -2,6 +2,7 @@
 
 import asyncio
 from abc import ABC, abstractmethod
+from collections import defaultdict
 from typing import TYPE_CHECKING
 
 if TYPE_CHECKING:
@@ -15,11 +16,14 @@ class TraceScheduler(ABC):
     """
 
     @abstractmethod
-    async def select_trace(self, trace: DSTrace) -> tuple[int, ...]:
+    async def next(self, trace: DSTrace) -> tuple[int, ...]:
         """
         Selects the next trace to expand.
 
-        This method must be async to allow for safe concurrent access.
+        For proposing selections, we have to follow the rules
+        - Suggest selection: suggest a selection that is suitable for the current trace.
+        - Suggested should be garenteed to be recorded at last!!!
+        - If no suitable selection is found, the function should async wait!!!!
 
         Args:
             trace: The DSTrace object containing the full experiment history.
@@ -39,31 +43,33 @@ class RoundRobinScheduler(TraceScheduler):
     NOTE: we don't need to use asyncio.Lock here as the kickoff_loop ensures the ExpGen is always sequential, instead of parallel.
     """
 
-    def __init__(self):
+    def __init__(self, max_trace_num: int):
+        self.max_trace_num = max_trace_num
         self._last_selected_leaf_id = -1
+        self.rec_commit_idx = 0  # the node before rec_idx is already committed.
+        self.uncommited_rec_status = defaultdict(int)  # the uncommited record status
 
-    async def select_trace(self, trace: DSTrace) -> tuple[int, ...]:
+    async def next(self, trace: DSTrace) -> tuple[int, ...]:
         """
         Atomically selects the next leaf node from the trace in order.
         """
-
-        leaves = trace.get_leaves()
-        if not leaves:
-            # This is the very first experiment in a new tree.
-            return trace.NEW_ROOT
-
-        # Find the index of the last selected leaf in the current list of leaves
-        try:
-            current_position = leaves.index(self._last_selected_leaf_id)
-            # Move to the next position, wrapping around if necessary
-            next_position = (current_position + 1) % len(leaves)
-        except ValueError:
-            # This can happen if the last selected leaf is no longer a leaf
-            # (it has been expanded) or if this is the first selection.
-            # In either case, start from the beginning.
-            next_position = 0
-
-        selected_leaf = leaves[next_position]
-        self._last_selected_leaf_id = selected_leaf
-
-        return (selected_leaf,)
+        while True:
+            # step 0: Commit the pending selections
+            for i in range(self.rec_commit_idx, len(trace.dag_parent)):
+                for p in trace.dag_parent[i]:
+                    self.uncommited_rec_status[p] -= 1
+            self.rec_commit_idx = len(trace.hist)
+
+            # step 1: select the parant trace to expand
+            # Policy: if we have fewer traces than our target, start a new one.
+            if trace.sub_trace_count + self.uncommited_rec_status[trace.NEW_ROOT] < self.max_trace_num:
+                self.uncommited_rec_status[trace.NEW_ROOT] += 1
+                return trace.NEW_ROOT
+
+            # Step2: suggest a selection to a not expanding leave
+            leaves = trace.get_leaves()
+            for leaf in leaves:
+                if self.uncommited_rec_status[leaf] == 0:
+                    self.uncommited_rec_status[leaf] += 1
+                    return (leaf,)
+            await asyncio.sleep(1)