NAME
msgmax — maximum System V IPC message size in bytes
VALUES
Allowed values
Minimum: 0
Maximum:
(64*1024*1024),
(msgssz*msgseg),
or
msgmnb,
whichever is smaller.
DESCRIPTION
The
msgmax
tunable specifies the maximum allowable size, in bytes, of any single message
in a System V message queue.
msgmax
must be no larger than
msgmnb
(the size of a queue) nor can it be larger than the preallocated system-wide
message storage space
(msgssz*msgseg).
Possible strategies for deciding this tunable value include setting it equal
to
msgmnb
(one message per queue) or the size of the biggest expected message which
is less than
msgmnb.
Any
msgsnd()
system call that attempts to send a message larger than
msgmax
bytes will return
EINVAL.
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
None. Changes affect subsequent
msgsnd()
operations.
When Should the Value of This Tunable Be Raised?
Raise this tunable when applications need to send larger messages.
When Should the Value of This Tunable Be Lowered?
Lower this tunable when applications are only using smaller message sizes.
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, changes to the
msgmax
tunable may also require changes to the
msgmnb,
msgssz,
and
msgseg
tunables.
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
msgmax
was developed by AT&T.
Printable version
