Delete all rviz markers

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I m using ROS Noetic in Ubuntu 20.04. Please see following code which creates 2 lines in each message and publishes over ROS network. When one message is received the previous message's lines are deleted. Includes are <ros ros.h=""> and <visualization_msgs marker.h="">. (I m not able to add screen recording here to show how it is seen in RViz.)

int main( int argc, char** argv ) 
{
  ros::init(argc, argv, "points_and_lines");
  ros::NodeHandle n;
  ros::Publisher marker_pub = n.advertise<visualization_msgs::Marker>("visualization_marker", 10);
  ros::Rate r(1);

  int count = 0;

  visualization_msgs::Marker markerD;

  // Set the frame ID and timestamp.  See the TF tutorials for information on these.
  markerD.header.frame_id = "map";    
  markerD.action = visualization_msgs::Marker::DELETEALL;    
  geometry_msgs::Point p;

  while (ros::ok())
  {    
    visualization_msgs::Marker line_list;
    line_list.header.frame_id = "map";
    line_list.ns = "points_and_lines";
    line_list.action = visualization_msgs::Marker::ADD;
    line_list.pose.orientation.w = 1.0;
    line_list.type = visualization_msgs::Marker::LINE_LIST;
    line_list.scale.x = 0.1;
    line_list.header.stamp = ros::Time::now();
    // Line list is red
    line_list.color.r = 1.0;
    line_list.color.a = 1.0;

    marker_pub.publish(markerD);

    line_list.id = count;

    //Create end points of 1st line
    p.x = count;
    p.y = 0;
    p.z = 0;
    line_list.points.push_back(p);
    p.z += 1.0;
    line_list.points.push_back(p);

    //Create end points of 2nd line
    p.x = count;
    p.y = 2;
    p.z = 2;
    line_list.points.push_back(p);
    p.z += 1.0;
    line_list.points.push_back(p);

    count++;

    marker_pub.publish(line_list);

    r.sleep();
  }   
}