NAME
msgmap — number of entries in the System V IPC message space resource map
VALUES
Allowed values
Minimum: 3
Maximum: msgtql+2
or
msgtql+2,
whichever is lower.
DESCRIPTION
The
msgmap
tunable specifies the size of the message space resource map that
tracks the free space in shared IPC message space.
Each resource map entry is an offset-space pair which points to
the offset and size (bytes) of each contiguous series of unused message
space "segments".
Message queues are implemented as linked lists in shared memory.
Each message consists of one or more contiguous segments of
reserved memory space.
As messages are added and removed, the reserved shared memory
area can become fragmented.
Free-space fragmentation generally increases as message size variation
increases.
Since the resource map requires an entry pair for each fragment of
free space, excess fragmentation can cause the free-space map to
completely fill.
If the map is full when message space is acquired or released, the
system issues the
DANGER: mfree map overflow.
warning message.
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?
When the free-space map is full and the system issues the warning message
DANGER: mfree map overflow.
A larger value for
msgmap
can correct this issue.
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
msgmap
was developed by AT&T.
SEE ALSO
mesg(5),
msgmax(5),
msgmnb(5),
msgmni(5),
msgseg(5),
msgssz(5),
msgtql(5).
Printable version
