diff --git a/modules/prediction/container/obstacles/obstacle.cc b/modules/prediction/container/obstacles/obstacle.cc
index 5da5374873a419f25c1bf8706aae0eeb5dd870d5..1475d84ab52d272c289910d2e7bb4701ec3787cf 100644
--- a/modules/prediction/container/obstacles/obstacle.cc
+++ b/modules/prediction/container/obstacles/obstacle.cc
@@ -196,7 +196,7 @@ bool Obstacle::Insert(const PerceptionObstacle& perception_obstacle,
   }
 
   // Trim historical features
-  Trim();
+  DiscardOutdatedHistory();
   return true;
 }
 
@@ -392,7 +392,7 @@ void Obstacle::UpdateStatus(Feature* feature) {
 }
 
 bool Obstacle::SetId(const PerceptionObstacle& perception_obstacle,
-                     Feature* feature, int prediction_obstacle_id) {
+                     Feature* feature, const int prediction_obstacle_id) {
   int id = prediction_obstacle_id > 0 ?
       prediction_obstacle_id : perception_obstacle.id();
   if (id_ < 0) {
@@ -1486,20 +1486,16 @@ bool Obstacle::ReceivedNewerMessage(const double timestamp) const {
   return timestamp <= last_timestamp_received;
 }
 
-void Obstacle::Trim() {
-  if (feature_history_.size() < 2) {
-    return;
-  }
-  int count = 0;
+void Obstacle::DiscardOutdatedHistory() {
+  auto num_of_frames = feature_history_.size();
   const double latest_ts = feature_history_.front().timestamp();
-  while (!feature_history_.empty() &&
-         latest_ts - feature_history_.back().timestamp() >=
+  while (latest_ts - feature_history_.back().timestamp() >=
              FLAGS_max_history_time) {
     feature_history_.pop_back();
-    ++count;
   }
-  if (count > 0) {
-    ADEBUG << "Obstacle [" << id_ << "] trimmed " << count
+  auto num_of_discarded_frames = num_of_frames - feature_history_.size();
+  if (num_of_discarded_frames > 0) {
+    ADEBUG << "Obstacle [" << id_ << "] discards " << num_of_discarded_frames
            << " historical features";
   }
 }
diff --git a/modules/prediction/container/obstacles/obstacle.h b/modules/prediction/container/obstacles/obstacle.h
index 4c4767807cda2c810108cee855a41e09efeb4be8..d566ef923f35dd440f8e3ca27c30b29ac8603317 100644
--- a/modules/prediction/container/obstacles/obstacle.h
+++ b/modules/prediction/container/obstacles/obstacle.h
@@ -234,7 +234,7 @@ class Obstacle {
   void UpdateStatus(Feature* feature);
 
   bool SetId(const perception::PerceptionObstacle& perception_obstacle,
-             Feature* feature, int prediction_id = -1);
+             Feature* feature, const int prediction_id = -1);
 
   bool SetType(const perception::PerceptionObstacle& perception_obstacle,
                Feature* feature);
@@ -305,7 +305,7 @@ class Obstacle {
 
   void SetJunctionFeatureWithoutEnterLane(Feature* const feature_ptr);
 
-  void Trim();
+  void DiscardOutdatedHistory();
 
  private:
   int id_ = -1;
diff --git a/modules/prediction/container/obstacles/obstacles_container.cc b/modules/prediction/container/obstacles/obstacles_container.cc
index f528ead551ad2fe723e5c3fe49e30739dbed7000..38b17f7f6c97233fb01f4f95ffc96d169bfe3b8d 100644
--- a/modules/prediction/container/obstacles/obstacles_container.cc
+++ b/modules/prediction/container/obstacles/obstacles_container.cc
@@ -108,8 +108,8 @@ void ObstaclesContainer::Insert(const ::google::protobuf::Message& message) {
 }
 
 
-Obstacle* ObstaclesContainer::GetObstacle(const int id) {
-  auto ptr_obstacle = ptr_obstacles_.GetSilently(id);
+Obstacle* ObstaclesContainer::GetObstacle(const int perception_id) {
+  auto ptr_obstacle = ptr_obstacles_.GetSilently(perception_id);
   if (ptr_obstacle != nullptr) {
     return ptr_obstacle->get();
   }