TCP stack on most of the Linux distributions are tuned for the desktop. Using Linux distribution on servers having high load require some tuning on TCP stack. Here is what I found.
Add the following lines into /etc/sysctl.conf
# tcp tuning
net.ipv4.tcp_wmem=4096 65536 16777216
net.ipv4.tcp_rmem=4095 87380 16777216
sudo sysctl -p
Restart your application(s).
This is effective especially when clients are on slow connection. These configuration change will change the tcp write and read memory size so that lot many bytes can be sent over to client in a single packet.