NAME
msgssz — number of bytes in a System V IPC message segment
VALUES
Allowed Values
Minimum: 1
Maximum: (2^32-1)/"msgseg"
The product of
msgseg*msgssz
must not exceed a 32 bit integer value of 4,294,967,295 (2^32)-1.
DESCRIPTION
The
msgssz
tunable specifies the size, in bytes, of a "segment" of memmory space
reserved for storing IPC messages.
Space for messages is acquired in segment-sized increments as required
to contain the message.
Separate messages do not share segments.
The total available space for messages in the system is defined by the
product of
msgseg*msgssz,
the number of segments multiplied by the segment size.
It is best to select a segment size equal to the size of most messages
sent by applications.
This ensures optimal memory utilization of the segments.
For more information about System V message queues, refer to the
"Overview" section of the
mesg(5)
manpage.
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?
Raise this tunable if applications block too frequently in
msgsnd(),
requiring more or larger messages be held in the kernel message queues.
When Should the Value of This Tunable Be Lowered?
Lower this tunable when applications no longer require as much message space.
What Other Tunable Values Should Be Changed at the Same Time?
All the System V message queue tunables are interrelated and should
not
be treated as independent variables.
The set must be evaluated as a system to ensure the tunables reflect
the application requirements.
The
mesg
tunables include
msgmap,
msgmax,
msgmnb,
msgmni,
msgseg,
msgssz,
and
msgtql.
Specifically, the
msgseg
and
msgtql
tunables may need to be adjusted in conjunction with changes in the
msgssz
tunable.
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.
A table of message segments is allocated in kernel memory at boot time.
This memory is reserved whether or not it is used.
The memory requirement is the product the
msgssz
and
msgseg
tunables.
Use care when setting these two tunables, as they
can have a profound effect on memory utilization, due to the
multiplicative effect.
AUTHOR
msgssz
was developed by AT&T.
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