HP-UX 11i Release Notes (December 2000)

Process, Threads, Memory, and Kernel Parameters
System-V IPC Message Queue Enhancement (new)
Chapter 8164
System-V IPC Message Queue Enhancement
(new)
System-V IPC is the System-V InterProcess Communications package
developed byAT&T andcomprises mechanisms forarbitrary processes to
send and receive data “messages”, share virtual address space, and use
semaphores to synchronize execution. This enhancement applies only to
the message subsystem.
The System-V IPC kernel tunable MSGMNB, which sets the maximum
number of bytes on a queue, has had its maximum upper limit increased
from 64KB to 64MB. New or recompiled applications will automatically
use new, larger fields in the msqid_ds structure which describes queue
sizes. However, if queue sizes greater than 64KB are desired, a
compilation feature macro, “__BIGMSGQUEUE_ENABLED”, must be
defined. This may be done using the -D compiler option or the #define
pre-processor directive prior to any #include. (This requirement is
temporary and used to maintain compatibility during a transition
period.)
As hardware system capacities including CPU speed and memory have
increased, some customer and third-partyapplications have been placing
a greater demand upon the System-V IPC message queues. By
increasing the capacity of these queues, applications are able to transfer
large messages in a much more efficient manner. You will be able to
dedicate more system memory for this purpose. Also, this may ease
porting of some applications from other vendors’ platforms which use
message queues.
This enhancement is available on all systems.
Impact
There is no impact on system resources unless you increase system
memory dedicated to System-V IPC message queues. To do this, the size
of message memory segments (MSGSSZ) kernel tunable and/or the
number of these segments (MSGSEG) kernel tunable may need to be
increased.
An individual message queue cannot exceed the maximum queue size
(MSGMNB) kernel tunable. The size of an individual message cannot
exceed the MSGMAX kernel tunable.