Oracle now uses User Datagram Protocol (UDP) as the default protocol on Linux for interprocess communication, such as cache fusion buffer transfers between the instances. However, starting with Oracle 10g network settings should be adjusted for standalone databases as well.

Oracle recommends the default and maximum send buffer size (SO_SNDBUF socket option) and receive buffer size (SO_RCVBUF socket option) to be set to 256 KB. The receive buffers are used by TCP and UDP to hold received data until it is read by the application. The receive buffer cannot overflow because the peer is not allowed to send data beyond the buffer size window. This means that datagrams will be discarded if they do not fit in the socket receive buffer. This could cause the sender to overwhelm the receiver.

The default and maximum window size can be changed in the proc file system without reboot:

The default setting in bytes of the socket receive buffer:

# sysctl -w net.core.rmem_default=262144

The default setting in bytes of the socket send buffer:

# sysctl -w net.core.wmem_default=262144

The maximum socket receive buffer size which may be set by using the SO_RCVBUF socket option:

# sysctl -w net.core.rmem_max=262144

The maximum socket send buffer size which may be set by using the SO_SNDBUF socket option:

# sysctl -w net.core.wmem_max=262144

To make the change permanent, add the following lines to the /etc/sysctl.conf file, which is used during the boot process:

net.core.rmem_default=262144
net.core.wmem_default=262144
net.core.rmem_max=262144
net.core.wmem_max=262144

To improve fail over performance in a RAC cluster, consider changing the following IP kernel parameters as well:

net.ipv4.tcp_keepalive_time
net.ipv4.tcp_keepalive_intvl
net.ipv4.tcp_retries2
net.ipv4.tcp_syn_retries

Changing these settings may be highly dependent on your system, network, and other applications. For suggestions, see Metalink Note:249213.1 and Note:265194.1.

On Red Hat Enterprise Linux systems the default range of IP port numbers that are allowed for TCP and UDP traffic on the server is too low for 9i and 10g systems. Oracle recommends the following port range:

# sysctl -w net.ipv4.ip_local_port_range="1024 65000"

To make the change permanent, add the following line to the /etc/sysctl.conf file, which is used during the boot process:

net.ipv4.ip_local_port_range=1024 65000

The first number is the first local port allowed for TCP and UDP traffic, and the second number is the last port number.