tcphashsz.5 (2010 09)

t
tcphashsz(5) tcphashsz(5)
(Tunable Kernel Parameters)
NAME
tcphashsz - determines the size of the networking hash tables
VALUES
Failsafe
2048
Default
0
Allowed values
0 to 65536
Recommended values
0
A value of 0 (default) will adjust the
tcphashsz in proportion to the number of cores in the system. If
tcphashsz is set to a non zero value, it should be specified as a power of two. Otherwise, it will be
rounded down to the nearest power of two.
DESCRIPTION
This variable is used to set the size of the networking hash tables. HP recommends that the value of
tcphashsz be set to 0 so that the system can choose an optimal tcphashsz value. A system that is
going to have a large number of connections on it all of the time may see some benefit of increasing this
value, beyond the number determined by the system.
If this tunable is not set to zero, then it needs to be a power of two. If it is not specified as a power of two,
then it is rounded down to the nearest power of two. If this tunable is set in the range of 1 to 255, then it
will be increased to 256.
Who Is Expected to Change This Tunable?
Anyone.
Restrictions on Changing
Changes to this tunable take effect at the next reboot.
When Should the Value of This Tunable Be Raised?
This value may be raised in the case of a machine with a large number of connections that last for an
extended period of time.
What Are the Side Effects of Raising the Value?
More memory is used when this value is raised.
When Should the Value of This Tunable Be Lowered?
If a system is tight on memory and it has just a few connections on it, then lowering the value may
reclaim some memory.
What Are the Side Effects of Lowering the Value?
If
tcphashsz is set too low, the system will have long hash chains which will slow it down.
What Other Tunables Should Be Changed at the Same Time?
None.
WARNINGS
All HP-UX kernel tunable parameters are release specific. This parameter may be removed or have its
meaning changed in future releases of HP-UX.
Installation of optional kernel software, from HP or other vendors, may cause changes to tunable parame-
ter values. After installation, some tunable parameters may no longer be at the default or recommended
values. For information about the effects of installation on tunable values, consult the documentation for
the kernel software being installed. For information about optional kernel software that was factory
installed on your system, see HP-UX Release Notes at
http://www.hp.com/go/hpux-core-docs.
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1