NAME
msgseg — number of System V IPC message segments in the system
VALUES
Allowed Values
Minimum: 1
Maximum: 32767
or
((2^32-1)/msgssz),
whichever is smaller.
The product of
msgseg*msgssz
must not exceed a 32 bit integer value of 4,294,967,295 (2^32)-1.
DESCRIPTION
The
msgseg
specifies the total number of "segments" of system-wide shared memory
message storage space which is shared among all IPC message queues.
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.
If applications have consumed all message segments, the
msgsnd()
call will block until segments become available or return
EAGAIN
if
IPC_NOWAIT
was specified.
Messages larger than a single segment are allocated in a number of
contiguous segments sufficient to hold the message.
As all segments are allocated as a table (contiguous memory),
fragmentation can occur as messages are added and removed.
Therefore, if message sizes often exceed a single segment,
consider allocating more segments than are actually needed
for message data, to allow for some fragmentation.
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
msgssz
and
msgtql
tunables may need to be adjusted in conjunction with changes in the
msgseg
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
msgmni
was developed by AT&T.
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