HP-UX Reference (11i v2 03/08) - 5 Miscellaneous Topics, 7 Device (Special) Files, 9 General Information, Index (vol 9)

m
msgmap(5) msgmap(5)
(Tunable Kernel Parameters)
NAME
msgmap - number of entries in the System V IPC message space resource map
VALUES
Failsafe
(2+msgtql)
Default
(2+msgtql)
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) man-
page.
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 vari-
ables. The set must be evaluated as a system to ensure the tunables reflect the application requirements.
The message 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.
SEE ALSO
msgrcv(2), mesg(5), msgmax(5), msgmnb(5), msgmni(5), msgseg(5), msgssz(5), msgtql(5).
Section 5−−180 Hewlett-Packard Company − 1 − HP-UX 11i Version 2: August 2003