Technical data

Tuning Techniques
2.1 Subsystem Attributes
Recommended Values
The default value of the inet subsystem attribute inifaddr_hsize is 32; the
maximum value is 512.
For the best performance, the value of the inifaddr_hsize attribute is always
rounded down to the nearest power of 2. If you are using more than 500 interface
IP aliases, specify the maximum value of 512. If you are using fewer than 250
aliases, use the default value of 32. For a number of aliases between 250 and
500, use a value that is a power of 2 between 32 and 512.
2.1.6.4 Increasing the TCP Partial Connection Timeout Rate
If increasing the
somaxconn limit does not prevent the listen queue from filling, or
if the default grows to an excessive length, you can make partial connections time
out sooner by decreasing the value of the
inet subsystem attribute tcp_keepinit .
The tcp_keepinit attribute specifies the amount of time that a partial connection
remains on the socket listen queue before it times out. Partial connections
consume socket listen queue slots and fill the queue with connections in the SYN_
RCVD state.
Performance Benefits and Tradeoffs
Network performance can degrade if a client overfills a socket listen queue
with TCP SYN packets, thereby blocking other users from the queue. To
eliminate this problem, increase the value of the
sominconn attribute to its
maximum value. If the system continues to drop SYN packets, decrease the
value of the tcp_keepinit attribute to 30 (15 seconds). Monitor the values of
the sobacklog_drops and somaxconn_drops attributes to determine whether the
system is dropping packets. (See Section 2.1.7 for more information about event
counters.)
You can modify the
tcp_keepinit attribute without rebooting the system.
When to Tune
Modify the TCP partial-connection timeout limit if the value of the
somaxconn_drops attribute increases often. If this occurs, decrease the value
of the tcp_keepinit attribute.
Recommended Values
The value of the
tcp_keepinit attribute is in units of 0.5 seconds. The default
value is 150 units (75 seconds). If the value of the sominconn attribute is 65535,
use the default value of the tcp_keepinit attribute.
If you set the value of the tcp_keepinit attribute too low, you may prematurely
break connections associated with clients on network paths that are slow or
network paths that lose many packets. Do not set the value to less than 20 units
(10 seconds).
2.1.6.5 Slowing TCP Retransmission Rate
The
inet subsystem attribute tcp_rexmit_interval_min specifies the minimum
amount of time before the first TCP retransmission.
Performance Benefits and Tradeoffs
You can increase the value of the tcp_rexmit_interval_min attribute to slow
the rate of TCP retransmissions, which decreases congestion and improves
performance.
You can modify the tcp_rexmit_interval_min attribute without rebooting the
system.
Tuning Techniques 2–11