Does subscriber drop message according to message size?

[TaoYibo1866]

I have two nodes, "publisher" and "subscriber". The 'publisher' publishes ByteMultiArray messages in 50Hz, with "queue_size=1". The "subscriber" subscribes to the 50Hz topic with "queue_size=1", and publishes output in the callback function.

When the ByteMultiArray message is less than 508 bytes, everything goes as expected and the callback function is executed in 50Hz. However, when the message is bigger than 508 bytes, callback frequency drops to 28Hz. This is wired.

publisher.cpp

#include <ros/ros.h>
#include <std_msgs/ByteMultiArray.h>

using std_msgs::ByteMultiArray;

int main(int argc, char **argv)
{
  ros::init(argc, argv, "publisher");
  ros::NodeHandle nh;
  ros::Publisher bytes_pub = nh.advertise<ByteMultiArray>("bytes", 1);
  ros::Rate r(50);
  while (ros::ok())
  {
    ByteMultiArray msg;
    msg.data.resize(508);
    bytes_pub.publish(msg);
    ros::spinOnce();
    r.sleep();
  }
  return 0;
}

subscriber.cpp

#include <ros/ros.h>
#include <std_msgs/ByteMultiArray.h>
#include <std_msgs/Empty.h>

using std_msgs::ByteMultiArray;
using std_msgs::Empty;

void odomCb(ByteMultiArray msg)
{
  static ros::NodeHandle nh;
  static ros::Publisher pub = nh.advertise<Empty>("callback", 1);
  Empty empty;
  pub.publish(empty);
}

int main(int argc, char **argv)
{
  ros::init(argc, argv, "subscriber");
  ros::NodeHandle nh;
  ros::Subscriber bytes_sub = nh.subscribe<ByteMultiArray>("bytes", 1, odomCb);
  ros::spin();
  return 0;
}

rostopic hz /callback

subscribed to [/callback]
average rate: 30.048
min: 0.000s max: 0.044s std dev: 0.01621s window: 29
average rate: 28.119
min: 0.000s max: 0.048s std dev: 0.01442s window: 56
average rate: 27.588
min: 0.000s max: 0.048s std dev: 0.01386s window: 82
average rate: 27.553
min: 0.000s max: 0.048s std dev: 0.01376s window: 110
average rate: 27.373
min: 0.000s max: 0.048s std dev: 0.01351s window: 136

rostopic hz /bytes

subscribed to [/bytes]
average rate: 49.993
min: 0.000s max: 0.048s std dev: 0.01723s window: 50
average rate: 49.997
min: 0.000s max: 0.048s std dev: 0.01895s window: 99
average rate: 49.999
min: 0.000s max: 0.048s std dev: 0.01949s window: 150
average rate: 49.974
min: 0.000s max: 0.048s std dev: 0.01980s window: 199

[TaoYibo1866]

My machine is running Ubuntu 20.04, ROS Noetic.

[TaoYibo1866]

Using
ros::Subscriber bytes_sub = nh.subscribe<ByteMultiArray>("bytes", 1, odomCb, ros::TransportHints().tcpNoDelay()); fix message drop. Still wonder why though.