%% Inter-Process Communication (IPC) Parameters
%C Inter-Process Communication (IPC) Parameters
The following tunable parameters
are associated with inter-process
communication messages, semaphores and shared data.
All memory and data structures for the semaphore IPC are
dynamically allocated as needed.
%%% Message Queue Parameters
%C Message Queue Parameters
All memory for message queues is dynamically allocated as needed.
MSGTQL is autotuned.
MSGMNI, the maximum number of
messages in the system, is set in the autotune file.
The total amount of memory that can be allocated for message
queues is limited by (msginfo.msgssz * msginfo.msgseg).
Only the product of these two is important, neither is used on its own.
% MSGMAX
Specifies the maximum size of a message.
The default value is 2048.
% MSGMNB
Specifies the maximum size of a message queue in bytes.
The sum of all messages on a queue cannot be more than MSGMNB.
The default value is 4096.
% MSGSSZ
MSGSSZ is not used directly,
but is multiplied by
MSGSEG
to compute the total number of bytes allocated to
messages system-wide.
% MSGSEG
The default value is 1
and the value of
MSGSSZ
times the value of
MSGSEG
determines the size of the pool available for messages.
Keep in mind,
so you can balance the amount allocated to this pool
with the amount needed by the rest of the system,
that this memory is allocated from
the kernel memory allocator (KMA).
The maximum amount of kernel memory
that can be allocated is 16MB.
%%% Semaphore Parameters
% SEMAEM
Specifies the adjustment on exit for maximum value,
alias
semadj.
This value is used when a semaphore value becomes greater
than or equal to the absolute value of
semop(2),
unless the program has set its own value.
% SEMMNI
Specifies the number of semaphore identifiers
in the kernel.
This is the number of unique semaphore sets
that can be active at any given time.
The default value is 10.
The maximum value is autotuned.
% SEMMSL
Specifies the maximum number of semaphores per semaphore identifier.
The default value is 25.
% SEMOPM
Specifies the maximum number of semaphore operations that can be
executed per semop(2) system call.
The default value is 10.
% SEMUME
Specifies the maximum number of undo entries per process.
The default value is 10.
% SEMVMX
Specifies the maximum value of a semaphore.
The default value is the maximum value for this parameter.
%%% Shared Memory Parameters
% SHMMAX
Specifies the maximum shared memory segment size.
% SHMMIN
Specifies the minimum shared memory segment size.
% SHMMNI
Specifies the maximum number of
shared memory identifiers system wide.
% SHMSEG
Specifies the number of
attached shared memory segments [or identifiers] per process.
The default value is 6.
The maximum number of shared memory segments
that can be attached per process
is dependent on the available unused space the process has.
So even if a process has fewer than
SHMSEG
shared memory segments, it
may not be able to attach another
because of its limited space.
