(Dist) Tune Linux systems

Tasks

Configure the following settings and variables according to your tuning needs:

• Changing TCP parameters

  • Linux offers a number of tunable TCP parameters whose default values might be sufficient for WAS. It might be necessary to tune these parameters in some exceptional cases. For example, we might reduce the number of sockets in specific states such as TIME_WAIT, modify the TCP keepalive operation, or modify other functions.

  • How to view or set:

    Consult the detailed information available under "man tcp" under your Linux distribution.

• Linux file descriptors (ulimit)

  • Number of open files that are supported. The default setting is typically sufficient for most applications. If the value set for this parameter is too low, a file open error, memory allocation failure, or connection establishment error might be displayed.

  • How to view or set: Check the UNIX reference pages on the ulimit command for the syntax of different shells. To set the ulimit command to 8000 for the KornShell shell (ksh), issue the ulimit -n 8000 command. Use the ulimit -a command to display the current values for all limitations on system resources.

  • Default value: For SUSE Linux Enterprise Server 9 (SLES 9), the default is 1024.

  • Recommended value: 8000

• Connection backlog

  • Change the following parameters when a high rate of incoming connection requests result in connection failures:

    echo 3000 > /proc/sys/net/core/netdev_max_backlog
    echo 3000 > /proc/sys/net/core/somaxconn

• TCP_KEEPALIVE_INTERVAL

  • Determines the wait time between isAlive interval probes.

  • How to set:
    echo 15 > /proc/sys/net/ipv4/tcp_keepalive_intvl

  • Default value: 75 seconds

  • Recommended value: 15 seconds

• TCP_KEEPALIVE_PROBES

  • Determines the number of probes before timing out.

  • To set:
    echo 5 > /proc/sys/net/ipv4/tcp_keepalive_probes

  • Default value: 9 seconds

  • Recommended value: 5 seconds

This tuning procedure improves performance of WAS on the Linux operating system.

What to do next

After tuning the operating system for performance, consult other tuning topics for various tuning tips.

Tune Windows systems

Tune AIX systems

Tune Solaris systems

Tune HP-UX systems