NAME
msgssz — number of bytes in a System V IPC message segment
VALUES
Allowed Values
Greater than or equal to
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.
Some space may be unused and inaccessible in the last segment
acquired while the message remains stored.
The potential for fragmentation should be considered.
The total available space for messages in the system is defined by the
product of
msgseg*msgssz
or, the number of segments multiplied by the segment size.
Changing the ratio between these two tunables changes the granularity for
message storage and therefore the fragmentation to be expected
for any given message usage pattern.
Note that the total number of segments in the system is defined by
msgseg,
and
msgssz*msgseg
is the total message storage space.
Set
msgssz*msgseg
equal to or grater than the maximum a single large message queue
can hold.
msgssz
is the "granularity" for message storage.
For example, if
msgssz
is equal to 256,
then a 257-byte message will consume two segments.
If
msgssz
is equal to
8
(the default),
msgseg
is limited to 2^29 (536,870,912) because
msgssz*msgseg
is limited to an unsigned long.
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?
If increasing
msgseg
(the number of segments) will cause the total message space
(msgssz*msgseg)
to exceed an unsigned 32-bit value.
It has direct effect on reserved message space.
When Should the Value of This Tunable Be Lowered?
msgssz*msgseg
must remain greater than
msgmnb
and
msgmax.
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.
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.
AUTHOR
msgssz
was developed by AT&T.
SEE ALSO
mesg(5),
msgmap(5),
msgmax(5),
msgmnb(5),
msgmni(5),
msgseg(5),
msgtql(5).
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