msgtql(5)

NAME

msgtql — maximum number of System V IPC messages in the system at any time

VALUES

Default

1024

Failsafe

1024

Allowed values

Minimum: 1

Maximum: msgseg

Recommended values

The largest number of messages expected.

DESCRIPTION

The msgtql tunable specifies the maximum total system-wide individual messages across all message queues. Every message has a header to specify message type and location and the total number of headers is limited by msgtql.

Note that if a msgsnd() system call attempts to exceed the limit imposed by msgtql, it will block until message space becomes available or return EAGAIN if IPC_NOWAIT is set.

Other kernel tunables may limit the maximum number of messages supported. Limiting factors can be msgmnb, the maximum number of bytes in a queue, or msgseg, the maximum number of message segments.

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 if applications block too frequently in msgsnd(), requiring more total messages be held in the kernel message queues.

When Should the Value of This Tunable Be Lowered?

Lower this tunable when applications no longer require as many total messages.

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, the msgseg or msgssz tunables may need to be adjusted along with 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

msgtql was developed by AT&T.