msgmap(5)

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) 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 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.

Installation of optional kernel software, from HP or other vendors, may cause changes to tunable parameter values. After installation, some tunable parameters may no longer be at the default or recommended values. For information about the effects of installation on tunable values, consult the documentation for the kernel software being installed. For information about optional kernel software that was factory installed on your system, see HP-UX Release Notes at http://docs.hp.com.

AUTHOR

msgmap was developed by AT&T.