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Tuning Sysctl Paramaters For Heavily Loaded Systems

Stewart -

If you are running a large Atmail cluster with multiple machines, you can further optimize the performance of the application by tuning the systems sysctl values for networking. One common issue is on a highly loaded system, the max number of TCP connections can exceed between hosts, or too many connections are in the idle state.


  • On-Premise Server + WebMail Installations: Version 6.0 > Current Version


  • Heavy load


We recommend the following be applied to the /etc/sysctl.conf

Client machines:

net.ipv4.tcp_fin_timeout = 10

Close connections in the TCP FIN timeout state 10 seconds ( default 60 )

net.ipv4.ip_local_port_range = "15000 61000"

Increase the range of ports available for client connections ( default 32768 61000 )

Server machines (e.g mysql server or main machine)

net.ipv4.tcp_fin_timeout = 10

Same value as clients

net.core.somaxconn = 1024 ( default 128 )

The net.core.somaxconn value has an important role. It limits the maximum number of requests queued to a listen socket.

net.core.netdev_max_backlog = 2000 ( default 1000 )

After editing the /etc/sysctl.conf you can reboot the machine, otherwise set the paramater directly on the CLI using:

/sbin/sysctl net.core.netdev_max_backlog = 2000

This is just another tip for tuning the performance of an Atmail system, from the default stock Linux OS.

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