NAME
msgmap — number of entries in the System V IPC message space resource map
VALUES
Allowed values
Minimum: 3
Maximum: msgtql+2
or
msgseg+2,
whichever is lower.
Recommended Value
msgtql+2
DESCRIPTION
The
msgmap
tunable specifies the size of (number of entries in) 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".
If the map is full when message segments are released (e.g., by
msgrcv()),
the system issues the
DANGER: mfree map overflow.
warning message, and those segments will be left unusable.
The
msgtql
tunable determines how many messages can exist. At maximum, there
can be one free range of segments between each real message.
So, there can be
msgtql+1
free segment ranges.
One additional map entry is required for accounting
information, so the recommended value for the
msgmap
tunable is
msgtql+2.
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 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.
Specifically, changes to the
msgmap
tunable should be made whenever there are changes to the
msgtql
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.
AUTHOR
msgmap
was developed by AT&T.
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