mjhjmtu

I have a java server application.

 while(true)
 
 serverSocket.receive(receivePacket);
 process(receivePacket);
 serverSocket.send(sendPacket);
 try 
 Thread.sleep(10000); // sleep for 10s
 catch (InterruptedException e) 
 e.printStackTrace();
 
 

It receives and processes 1 UDP packet / 10 sec.

If I send 10 UDP packets to the server processes 1 packet and then goes to sleep for 10s. so I get the 10th packet's response after 100s.

If I do this is server1 with CentOS release 6.4 (Final).

Server 1: cat /proc/net/udp
 sl local_address rem_address st tx_queue rx_queue tr tm->when retrnsmt uid timeout inode ref pointer drops 
 110: 00000000:10AE 00000000:0000 07 00000000:00000000 00:00000000 00000000 0 0 85635445 2 ffff880836e6d100 0 
 111: 00000000:10AF 00000000:0000 07 00000000:00000000 00:00000000 00000000 0 0 85635446 2 ffff88083913a1c0 0 
 115: 00000000:15B3 00000000:0000 07 00000000:00004FC8 00:00000000 00000000 0 0 390649369 2 ffff880434ae7440 0 
 117: 02FE6341:0035 00000000:0000 07 00000000:00000000 00:00000000 00000000 0 0 353480394 2 ffff8808367f9040 0 

If I do this same thing in server 2:

Server 2: cat /proc/net/udp
 sl local_address rem_address st tx_queue rx_queue tr tm->when retrnsmt uid timeout inode ref pointer drops 
 4: FCA9C11F:C36F 8C719AC6:0035 01 00000000:00000000 00:00000000 00000000 0 0 2983494501 2 ffff880169aff4c0 0 
 5: FCA9C11F:D3F0 8C719AC6:0035 01 00000000:00000000 00:00000000 00000000 0 0 2983494485 2 ffff8801b9bbedc0 0 
 16: 7A52BB59:007B 00000000:0000 07 00000000:00000000 00:00000000 00000000 38 0 2438608536 2 ffff8807656764c0 0 
 16: A2EE0D55:007B 00000000:0000 07 00000000:00000000 00:00000000 00000000 38 0 2438608045 2 ffff88077ccdd7c0 0 
 16: A58F466D:007B 00000000:0000 07 00000000:00000000 00:00000000 00000000 38 0 2438607809 2 ffff8801129f6240 0 

They are both centos servers and as we can see that the server1's rx_queue buffer is increasing as the application is processing packets slower than data is coming to the server.

I did this exact same thing in server2 but in server2 the rx_queue is not increasing.
what am I doing/understanding wrong?